6 Gas Saving Myths… Debunked

CNNMoney has compiled a list of gas saving myths and asked Consumer Reports and Edmunds.com to debunk them. Here’s the list:

#1. Fill your tank in the morning

Consumer Reports says that the temperature variation in a single day isn’t really significant enough to affect the gas, so you might as well stay in bed.

#2. Change your air filter

“Modern engines have computer sensors that automatically adjust the fuel-air mixture as an increasingly clogged air filter chokes off the engine’s air supply.”

#3. Use premium fuel

“When sensors detect regular instead of premium fuel, the system automatically adjusts spark plug timing. The result is a slight reduction in peak horsepower – really, you’ll never notice – but no reduction in fuel economy.”

#4 Pump up your tires

“According to on-the-road driving tests by both Consumer Reports and auto information site Edmunds.com, underinflated tires reduce fuel economy, so proper inflation is key.

But you should never over-inflate your tires.

#5 To AC or Not To AC
At most speeds and in most vehicles, A/C use drains slightly more fuel than driving with the windows down, contends David Champion, head of auto testing for Consumer Reports. “My final take on is that it’s very close,” says Phil Reed, consumer advice editor for Edmunds.com. “It’s hard to measure the difference and every vehicle is different.”

#6. Bolt-ons and pour-ins

“… if there really was an additive that made gas burn up more slowly, it wouldn’t be sold over the Internet one bottle at a time.”

There’s more detailed info at CNNMoney, but as far we’re concerned, the best way to increase your fuel economy is to slow down, stop running up on people’s ass and then slamming on the brakes, and don’t weave from lane to lane trying to find the fast one. They’re all slow. Such is life. Relax.

6 gas saving myths [CNNMoney] (Thanks, Aaron!)

(Photo: meghannmarco )


Edit Your Comment

  1. SkokieGuy says:

    Great photo!

    Folsom Street, gee, the gas prices sure are high, but what does a lube job cost?

  2. grandzu says:

    But what about the Hydro-4000? 9 MPG to 23 MPG!!

  3. statnut says:

    @SkokieGuy: $2 bucks, but only in the alley.

  4. jasezero says:

    This article does assume your car has been properly maintained through tune ups. If you haven’t done that in a while…well then you are most likely wasting gas.

  5. Some of those can be true, depending on vehicle, but all of it is generally correct. You should never overinflate your tires FOR SAFETY REASONS, but it will definitely improve your mileage. Similary, really hard tires provide low rolling resistance, but will also compromise your handling and braking ability. My view is “what good is saving a dollar a tank on fuel when I end up getting into an accident because of crappy tires?” Sticky tires FTW.

    Another good one I read on the tdi forums (harcore diesel drivers) is that “every time you press the brakes, it’s like pouring fuel on the ground”. Keep a nice buffer zone and use drivetrain braking. This is where it helps to drive a manual tranny, since autos tend to want to stay in overdrive as long as possible. Manually shifting an auto excessively can wear out your torque converter prematurely.

  6. nursetim says:

    Mythbusters took on #6 and came to the same conclusion (insert comment about how unscientific Mythbusters is here). I am surprised about the air filter, though.

  7. 1. Find the economy sweet spot for your car (usually around 50 MPH – tailgaters can bite my painted metal ass), and set your cruise control accordingly.

    2. Combine trips.

    3. Share rides.

    4. Ask yourself what people asked each other during the World War Two years – is this trip really necessary?

    I’ve gone without an oil change for five months because I still haven’t driven my car 3000 miles, mainly because of the above. I fill my car every other week, and even with gas pushing four bucks, it still only costs me around thirty bucks.

  8. Anitra says:

    #1 won’t save you gas, but it will save you money. Why? Because the gas stations (around here, anyway) change their prices around noon.

  9. Balisong says:

    I think Mythbusters found that at speeds up to (if I’m remembering correctly) 45 mph windows open worked better and over 45 mph AC worked better at saving gas. I’ve always figured the difference saved would be so slight it doesn’t matter though.

  10. jscott73 says:

    Here here on the slow down and stop weaving advice. People are non-stop complaining about the price of gas then they get in their cars and gun it and try to fly down the freeway as fast as they can. I cruise along at 70mph on my way to work and get past left and right, and this is on San Diego’s busy freeways, with gas over $4/gallon your an idiot to be speeding so fast.

  11. Dobernala says:

    Some of these are bogus debunkings. I’ve worked on newer cars where replacing old filters definitely brought the fuel economy up to par. Same with the premium fuel. You can’t make these sorts of generalities and pass them off as facts.

  12. mac-phisto says:

    meg – i beg to differ on that last part. have you ever heard of the racing term drafting? i save $20-$30 in gas/week by riding up on people’s asses. XD

  13. Tgg says:

    How driving with a pickup’s tailgate down?

    Huge myth, and I see people with their gates down all the time (or their gate replaced with something wind will go through).

  14. Nighthawke says:

    Engine computers do not detect what octane you have in your tank, but how your engine performs from it. All the system will do is adjust again and again for the best BALANCE between performance and economy. Oh, and emissions too.

  15. B says:

    @mac-phisto: And you’ll save even more when it kills you.

  16. HIV 2 Elway says:

    Gas Saving Tip #7 – Drive less.

  17. HIV 2 Elway says:

    Also, I get a kick out of the Missoura rednecks who write letters to the editor bitching about gas prices and then pass people on the right shoulder in excess of 90 mph.

  18. @Ash78: Most of those drivers are driving vehicles with transmissons/clutches made for doing the braking. Passenger vehicles are definitely not made for that, and should not be used as brakes. What they mean by hitting the brakes/dumping fuel is that the gas you used getting up to that speed is wasted, and the gas you use getting back on earlier is wasted, when if you gave yourself time/space, it doesn’t waste so much.

  19. Nighthawke says:

    @nursetim: They just about got themselves kill in the process too. After they got done disposing of the water cracker, they fed hydrogen directly into the carburetor. They wound up getting a massive backfire that lit the hose attached directly to the gas cylinder! It could have been worse, but that’s a frightening event especially if you don’t have a backcheck valve in the line.

  20. @Tgg: My undergrad is aero engineering- we did a study on that- complete bunk. Good call.

  21. sleze69 says:

    #6 – I guess this goes for gassers but Stanadyne is a great additive for diesel engines. At the current price of diesel it actually cheaper to use Stanadyne performance with every tank because of the savings from the increased mileage(5-10%).

    As far as I know, it is the only fuel additive that VW endorses. The rest is probably snake oil.

  22. Dobernala says:

    @HIV 2 Elway: Racism FTL!

  23. boandmichele says:

    i bought an 86 toyota mr2 for my daily driver (mr2’s are the best cars ever). stock is about 35 mpg, and therefore my mr2 has paid for itself almost twice in the 6 months ive driven it over my (pos) cadillac.

    then, after reading an article on those hypermilers (insane people who do insane things and achieve 100+ mpg), ive decided to attempt 50 mpg in my car.

    thus far, ive gone 97 miles, and its still on F. this is mostly just driving slowly, calmly, coasting a lot, and trying to NOT need the brakes.

  24. Solly says:

    Speaking of keeping tires inflated properly – does anyone know the accuracy of different types of air pressure gauges? 10% off is 3 psi for a tire holding 30 psi, 1% would be 0.3 psi – I’m just curious.

  25. Saboth says:


    I’m not sure rednecks qualify as a race quite yet.

  26. Folsom street…. but with gas prices being THAT high, it’s more like Folsom PRISON.

    The ring of fire… the ring of fire….

  27. #4 is crucial. I realized i was nearly 10psi low in two of my tires and it boosted my total miles per tank by a few good %

  28. @mac-phisto: HHHAAA! I had a bumper sticker to that effect years ago….
    I’m not Tailgating… I’M JUST DRAFTING.

  29. Snarkysnake says:

    Re : # 6

    You mean to tell me that the spam email that I have been getting about “saving $.70 a gallon” by pouring this stuff into my engine is a LIE ? It’s CLINICALLY PROVEN,for Gods sake ! Over 26 gajillion miles of testing ! The huge oil companies don’t want you to know just how much this stuff can save you !

    I for one,am shocked, SHOCKED that someone would lie to me in and EMAIL !

  30. AaronZ says:

    @Dobernala: “Some of these are bogus debunkings. I’ve worked on newer cars where replacing old filters definitely brought the fuel economy up to par. Same with the premium fuel.”

    We’re not just talking fuel savings, but overall cost savings.
    *If* you get better MPG from premium, does paying an extra .20 cents a gallon put you in the positive or negative for cost savings?
    Same thing with a filter… does spending $7 on a new filter save you a corrosponding $7 worth of gas milleage improvement?
    My guess would be ‘no’ since the improvements are so small as to be negligable when taking into account the associated costs.

    The best recomendation is about Tire pressure. That’s generally free (or a quarter), but provides actual improvement.

  31. Trai_Dep says:

    @verucalise: Funny enough, ring of fire also occurs around Folsom, well South of Market actually. But only when one party of the duo is especially well-endowed. And oddly, the other party is grateful afterwards.

  32. homerjay says:

    @Anitra: Yeah, but that only saves you money if they raise their prices at noon. What if they lowered them???

    HAHAHAHHAHAA! Sorry, I couldn’t resist a good joke.

  33. @Al Czerviks Ride: I follow you…I was just stating that it’s easier to maintain good distance when you have the benefit of drivetrain braking to modulate speed (all manuals and some automatics do a better job at this).

    Unfortunately, in most places, one person’s “safe following distance” is another jackass’s “gap to change lanes”…

  34. zidan says:

    They are generalizing too much. Some cars WILL get better mileage with premium fuel. For some cars the MFG doesn’t recommend premium fuel even though the engine is designed with it in mind b/c people would complain. So they just use the knock sensors so the car runs fine on regular, even though premium fuel would add more horsepower.

  35. ghank says:

    Almost the long weekend, get ready for the first of many Gas-Gouging-Long-Weekends coming soon to a gas station near you.

  36. QuantumRiff says:

    The Gas pedal doesn’t waste gas, the break pedal does.

  37. farker says:


    You do realize HIV 2 Elway said “rednecks” and not a member of a certain race, right? I believe it is YOU who is the racist :)

  38. @zidan: 80s K-cars and other Chrysler products that used the 2.2 engine ping like crazy on regular. That wastes gas. I used to put 91 octane in my Omni and get an improvement in mileage greater than the difference in price. Then I got a Honda Civic, which ran just as well on 87. Better engineering makes better performance.

  39. HIV 2 Elway says:

    @farker: @Saboth: Seriously, there are rednecks of all races and creeds

  40. crabbyman6 says:

    @mac-phisto: heh, I tell my wife that all the time. I still get hit for some reason though :(. I wonder how much of a difference this does make, on a few non-stop drives from FL to PA, “drafting” as much as I could my car got about 10mpg better than regular highway driving averages This was at speeds of at least 75mph, so not exactly in the ideal speed zone either.

  41. Ex_EA_Slave says:


    How driving with a pickup’s tailgate down?

    Huge myth, and I see people with their gates down all the time (or their gate replaced with something wind will go through).

    The problem with having the tailgate down or replaced with an air gate isn’t so much to do with mpg. The bed of the truck depends on the tailgate for support. Removing the tailgate will cause the structural integrity of the bed to fail and fall apart.

  42. xanadu1979 says:

    I think people should use the grade of gas that the manufacturer recommends. My car is supposed to have premium so I only put premium in it. And I disagree about not being able to tell the difference. With my last car I tried putting regular in even though premium was recommended and it felt like a different car. It wasn’t nearly as frisky.

  43. gamin says:

    Are people still thinking that putting 93 octane on their Kia sephia is gonna make it run better? Idiots

    Also come on the AC does drinks all your gas the Myth Buster already proved it

  44. theblackdog says:

    @SkokieGuy: You could probably get that for free.

  45. Ex_EA_Slave says:

    I call BS on the air filter. Yes, modern cars adjust the fuel/air mixture automatically, but that doesn’t mean the adjusted mixture is efficient. Engines are designed to run with a certain mixture. Adjusting this can and will cause problems. If less air is coming in, less fuel is also sprayed into the cylinder. The resulting ‘explosion’ may be less powerful than the engine needs to keep the pistons pumping in an efficient manner.

  46. @xanadu1979: Exactly correct. If your owner’s manual says to use at least 91 Octane gasoline, DO IT. High compression engines like the VW/Audi 1.8T and other (many German and Japanese performance engines) MUST be run on Premium – you can go for a tank on regular if you must, but regular use of, um, regular gas can damage the engine over time.

    That said, putting 92 Octane in your 1999 Ford Explorer with the tractor engine won’t benefit anyone by the oil company that makes a slightly higher profit margin on that grade.

    On the air filter tip, the logical conclusion is that fully occluding the air filter will result in a 100% increase in gas mileage. The point is that a dirty filter reduces performance, which tends to create heavier feet on the gas pedal. Just replace the air filter twice a year and be done with it.

    Ditto for oil; if you aren’t changing your oil at least twice a year (no matter what the mileage) you’re asking for trouble. Especially if you only take short trips, which creates acids in the oil by allowing condensates to remain in the oil instead of burning off.

  47. SOhp101 says:

    @jscott73: You’re an idiot for being in a lane where everyone passes you. Get the message. Move to the right please.

    Gas has gotten more expensive but I haven’t seen a significant decrease in my quality of life. In fact, the freeways have been clearer = less traffic = shorter commute times. Maybe high gas prices aren’t so bad after all.

  48. @Ex_EA_Slave: The problem with having the tailgate down or replaced with an air gate isn’t so much to do with mpg. The bed of the truck depends on the tailgate for support. Removing the tailgate will cause the structural integrity of the bed to fail and fall apart.

    I gotta question this. With a few unibody exceptions (Ridgeline), most trucks are just a ladder frame with a cab and a bed bolted on top. The bed is just a shell and shouldn’t involve any substantial load-bearing. What am I missing?

  49. SOhp101 says:

    @Ash78: The tailgate does help with aerodynamics–when up, it gives you the best fuel economy. Actually a bed cover gives you the absolute best but it is offset by the heavy weight it adds to your car.

  50. LatherRinseRepeat says:

    #4 Pump up your tires
    This is the easiest gas saving tip. Check your owners manual for the correct PSI. And make sure you check the PSI when the tires are cold, not after you’ve been driving around.

    #6. Bolt-ons and pour-ins
    I hope this is obvious to everyone. Damn those infomercials. :-)

  51. Ex_EA_Slave says:

    @gamin: “Are people still thinking that putting 93 octane on their Kia sephia is gonna make it run better? Idiots”,

    Engines have different compression ratios. A higher compression ratio means more fuel is being pumped into the cylinder before ignition. Using lower octane gas can cause the fuel/air mixture to ignite from compression, instead of the spark plug. This results in knocking. Higher octane gas can be more compressed before ignition in the cylinder. This allows for the pistons to go up and down faster, which turns the crankshaft faster, etc. I don’t know what the compression ratio is in a Kia Sephia, but if it is knocking, putting in 93 octane gas will stop the problem and make the car run better. You shouldn’t call someone an idiot for putting higher octane gas in their car. You should call them an idiot for buying a Kia in the first place.

  52. Ex_EA_Slave says:

    @Ash78: The bed itself will start to come apart without the tailgate. The frame of the truck will be fine. Think of a box. With all four sides, the box is relatively stable. Now take away one side of the box and notice how much sway there is in the remaining 3 sides. Over time, the bed walls begin to separate from the bed bottom which is securely bolted to the frame.

  53. @Trai_Dep: Everyone has a “ring of fire” these days after visiting the pump…. makes it hard to sit afterwards.

  54. theblackdog says:

    @Trai_Dep: @verucalise: All these buttsecks references, maybe this story belongs on Wonkette.

  55. TreyWaters says:

    @@AaronZ: Just based off rough calculations, at least in my car, the extra cost of Premium is cheaper than Regular. Car requires 91+ octane.

    I generally calculate mileage per tank every time I fill up, so this is where my numbers come from.

    Car: 2003 BMW Z4 3.0i

    93 octane: 29mpg
    87 octane: 21mpg (I did this on one tank just to see)


    93 octane: $.12/mile -> $38 / 300 miles (average per tank)
    87 octane: $.15/mile -> $45 / 300 miles

    QED, (at least on cars that benefit from/require higher octane) the extra cost may be worth it. YMMV, pun intended ;-)

  56. chandler in lasvegas says:

    Google: acetone gasoline

  57. @Ex_EA_Slave: Gotcha…never had a truck before. I know some of the flat-bed guys who add those small flip-down sides and tailgates–think about the Home Depot rental truck–but that’s a different beast altogether (since the flat bed isn’t integrated into the vehicle as completely as a standard bed is)

  58. chicagocooper says:

    @TreyWaters: Same goes for MINIs, 93 octane = 37mpg, 87 octane = 28 mpg.

  59. TreyWaters says:

    Oh, should have been more clear, $/mile costs assume premium = $3.50/gal, reg = 3.30/gal

  60. bobfromboston says:

    @zidan: Yes, you *might* get better mileage with premium gas. But enough to offset the 10 or 20 cents more per gallon that you’re paying? Highly unlikely.

    Similarly, you can spend $150 bucks for a complete engine tuneup, but it will be a long time before you recoup that money via any gas savings you might realize.

    By far you’ll save much more simply by driving less: combine your trips, share rides where possible, skip that trip to the mall. And if public transportation is an option where you live, try it, even just once or twice a week.

  61. jscott73 says:

    @SOhp101: The last I checked the speed limit where I drive is 65, going 70 would give me the right to be in whatever lane I want, if you want to be an idiot and waste gas to save a few minutes here and there then feel free to change lanes.
    That being said I almost always drive in the slow lane or one over unless there are big rigs to pass.

  62. t325 says:

    Another myth that needs debunking is coasting in neutral. Some people do it and claim it saves gas. I hear that all the time. Bbut not only is it dangerous and illegal in most places, it uses more gas than leaving your car in gear. When you’re in neutral, something needs to keep the engine going so it doesn’t stall, so it will use some fuel. In gear, with your foot off the gas, the movement of the wheels will keep the engine going so it doesn’t use any fuel.

    Regarding the whole premium thing….that’s what’s recommended I put in my car, and that’s what I put in my car. That’s one expense I’m willing to take. It’s a turbocharged engine, it needs premium for optimal performance.

  63. P_Smith says:

    @mac-phisto: meg – i beg to differ on that last part. have you ever heard of the racing term drafting? i save $20-$30 in gas/week by riding up on people’s asses.

    And have you ever heard of the racing term “brake test”? If you’re ever behind me on an open road with nobody else around, you’d better be paying attention.


  64. rouftop says:

    Or you could just listen to the Consumerist and turn off your engine after idling 10 seconds!

  65. kidgenius says:


    Yes, you are correct about outrightly calling everyone an idiot, but, if you car doesn’t say to specifically use a higher octane gas, then the higher octane gas in not needed, and no benefit will be derived from using it.

    @zidan: you’re a moron. Higher octane does not make you engine make more power. It allows your engine to make more hp, IF your engine has been tuned properly for the higher octane gas. All the octane rating is, is an indication of how susceptible the gasoline is to premature detonation. Basically, the higher the octane, the more you can compress it before it will explode. Higher compression ratios == more power.

  66. strangeffect says:

    Can we please stop mislabeling these things?

    The idea that tire inflation can help your mileage wasn’t debunked. Proving that something doesn’t work, except when it works, which is sometimes, is NOT debunking.

    Come on, we’re supposed to be pushing for honest labeling here.

  67. My car runs on indifference.

  68. P_Smith says:

    If you’re only doing in-city driving (and thus not likely to get stuck in the middle of nowhere), why not take the spare tire and jack out of the trunk, along with any other dead weight? If you actually do get a flat, a taxi ride home to pick up the gear isn’t that expensive. I’m surprised no one else has mentioned weight yet.

    Coasting is also an option, remembering the law of conservation of energy (an object in motion tends to etc.). Coming toward a red light, I coast to save on gas and also to stay in motion if I can anticipate the lights changing. This is good for everyday driving where you go the same route and know the lights, plus driving slow toward a red light is never a dangerous thing to do.

  69. BlackFlag55 says:

    The only way to save gas is set up a Darius wind rotor with a trickle line in a barrel of water that can collect the electrolyzed hydrogen released. Collect the hydrogen, use a solar generator to power a compression pump to fill your hydrogen fueled car or truck. Or, wait for the MDI Air Car, see above for a wind or solar generated electrical plant to run your compressed air tanks for filling the car.

    The only way to save gasoline is to switch to something else.

    However, you might check out Brown’s Gas. I know two local guys actually sort-of making this work, but it’s consuming their free time fiddling with it.

  70. The_Legend says:

    Consumer Reports had credibility? Since when?

  71. AustinTXProgrammer says:

    Engine braking does NOT help with gas milage. Any time you forcibly slow down a vehicle (except for hybrids with regenerative braking, and the computer handles it for you, press the peddle) you are converting kinetic energy to heat. It’s either in the brakes or engine. The engine isn’t worn by this, but your kinetic energy isn’t converted back to gas.

    Your engine converted gas into that kinetic energy, and to go again it has to do it again.

    The only way you can slow down without pouring gas on the ground (so to speak) is to shift into neutral and let an incline and aerodynamic drag slow you down.

    Engine braking does force other driving habits, such as following distance and slow deceleration, which will help your mileage.

  72. EdWedig says:

    It’s not going to save gas, but you should really fill you tank up after 6pm. When the sun is higher in the sky, it can convert the fumes coming from your fillup into ground-level ozone, which is hazardous to your health. By waiting until the evening, the sun is not as intense, and less of the gas gets converted.

    And, if you can fill up the night BEFORE the gas stations change their prices, even better.

  73. @AustinTXProgrammer: The one thing you’re forgetting is that the injectors are able to “shut off” (or very nearly) whenever engine braking is engaged in modern cars. So whenever you are slowing down while in gear, or holding your speed down a hill, you are using very little fuel at all.

    Compared with simply hitting the brakes (eg in an auto tranny), this is an improvement.

  74. @Ex_EA_Slave: A higher compression ratio means more fuel is being pumped into the cylinder before ignition.

    This is incorrect. Compression ratio means that when the cylinder reaches top dead center, the compression of gases inside the cylinder is at a certain ratio to atmospheric pressure. This compression is expressed as a the ratio of cylinder compression to atmospheric pressure – a typical high performance engine may have a 9:1 compression ratio or higher. Some turbocharged engines run over 11:1.

    Because compressing a gas causes heat, higher compression calls for higher octane gasoline, which does not detonate as easily without a spark. (Knocking and pinging are common names for this phenomenon.) Other causes of detonation not directly related to compression ratio are worn spark plugs, carbon deposits on valves and piston crowns, and a mis-timed engine.

  75. @TreyWaters: You car gets better mileage with higher octane gas because it is a higher compression engine, and when your BMW’s knock sensor “hears” detonation, it actually lengthens the injection pulse, squirting more gasoline into the cylinder to cool it the intake charge and retard detonation.

    Just another proof that if your car requires a certain grade of gas, it is important to use it – detonation can damage your engine in the long run, which costs a lot more than a few cents per gallon to repair.

  76. @chandler in lasvegas: While you’re at it, Google the cost of a new catalytic converter and the cost of a gallon of acetone. Not to mention the health hazards of handling acetone on a regular basis.

    Toluene is more effective, more toxic, less harmful to your car, and more difficult to procure when it comes to home-boosting your octane.

  77. MrEvil says:

    @Ash78: Uh, torque converters don’t wear out except in the lock-up clutch which is only used when you’re cruising in OD and not having to pull a steep grade. When accelerating or coasting, and even when you downshift, the torque converter goes back to being a fluid coupling. There’s a few vehicles that work a little different, the torque converter in my F250 stays locked up to 40 mph when coasting to a stop. This keeps the Diesel engine spinning and allows the injectors to shut down so the engine isn’t using any fuel during deceleration.

    You can have problems with mechanical shearing in the transmission fluid. But any auto owner familiar with cars knows to have it drained and flushed every so often. I do my autos once a year.

  78. drharris says:

    Regarding A/C, it’s borderline whether turning it off improves gas mileage significantly, but I do know that rolling your window down to compensate increases the drag enough to have a negative impact on your gas mileage. Bottom line: Always use A/C instead of rolling down your windows, at least at highway speeds.

  79. Ragman says:

    When I switched to a K&N air filter in my old car, it seemed to give me about another mile on my fuel economy. I didn’t expect it to, so I wasn’t checking mileage around the filter change. My average just went from the 28 range before, to the 29 range when I checked it some weeks after.

    AaronZ, where are you getting air filters for $7? Mine all cost $11 – $15 each.

    The biggest bump in fuel economy I’ve gotten was dropping to 5w-30 from 10w-30 oil in my old car. I got about 5 mpg out of that.

  80. howie_in_az says:

    @TreyWaters: I have the same engine as you (3-liter inline-6) in my 330i sedan, also from 2003. Try 89 octane; I haven’t noticed any mpg difference between it and 91 octane, and it’s ~$0.10 cheaper. Setting the cruise control at 74mph-ish I’ll get 33-34mpg.

  81. fever says:

    Obviously, the people who wrote these stories don’t live in Minnesota, or the desert. Specifically in the case of #1, when the temperature can drop to ~65 degrees Fahrenheit over night and then shoot back up to 95 by 10AM, it certainly does make a difference if you fill in the morning. Maybe not on the big fuel tank they put in the ground, but the gasoline vapors that come from one’s own fuel tank can be stifling. Why do you think they put those “vapor interlocks” on fuel pump spigots? Before anyone says that those are strictly to provide pressure to avoid backspray, rethink about how well they work.

    @BlackFlag55: lol, exactly.

  82. Doug81 says:

    As CaliforniaCajun said it’s important to use the grade of gas your car’s engine was designed to use. You can not only sacrifice some horsepower but also the longevity of the engine by using lower grade fuels. It’s just an important point that needs to be re-emphasized in light of the articles mis-information.

  83. Buckus says:

    That Mythbuster’s test about the A/C was so unscientific that its results could not be credible even to the average college graduate.

    On the first test, they used a device that measured the amount of air going into the engine and that calculated the mileage. They also ran the first test on the highway at different times of the day, the average speed was well above 60. This test concluded that MPG is higher with A/C on.

    On the second test, they poured a gallon of gas into two nearly-identical vehicles then drove till empty, one with A/C and one with windows-down. But they drove at an avg of 35 or 40 MPH. This test concluded that MPG is higher with windows-down.

    So they concluded that, overall, MPG is higher with windows down.

    Let’s recap, though. They used two different methods to calculate the MPG, ran the vehicles at different speeds during the tests, and ran one test in traffic and one on a controlled course. I’m no scientist, but I call BS on their conclusion because they did not repeat the test in a scientific manner when it would have been SO EASY to do.

    On a different note, I put mid-grade (89) gasoline in my Hyundai because the regular stuff causes the engine to knock.

    The reason tailgates up on pickup trucks works better is because the tailgate blocks air from leaving, creating a “bubble” of air that the higher-velocity air goes over. Anyone who’s ridden in the back of a pickup truck can testify to having a relatively calm atmosphere in the back even at highway speeds.

  84. quail says:

    A quick note on Myth #1: The real reason to fill up your tank in the morning or at night is to reduce the ozone caused by gas evaporating while you fill up your vehicle. Even with pumps that have the vapor reclamation systems you’ll hear it’s still a good idea to fill up at these times whenever ozone is at dangerous levels. (Source: Lived for years in the D/FW area.)

  85. thrillwill says:

    All I know is when I turn the AC on in my Integra acceleration drops like a stone. Hence I leave it off unless I really really have to.

  86. TechnoDestructo says:

    @Steaming Pile:

    It was 70mph in my Thunderbird. What are you driving, a full-size van?


    You know, you CAN see some benefits from following behind large trucks and motorhomes on the highway, while still obeying the 2 second rule.

  87. Geekybiker says:

    #1 true, but not by much
    #2 true, even if its not a lot. What a lot of BS about the fuel air mixture. Its about pumping losses. For example alot of cold air intakes end up providing a mpg or two over stock filter setups. More extreme than just a clean fitler, but similar idea.
    #3 depends. You’ll make more power if your car is designed for it and more power= less throttle. However low octane fuel is easier to ignite. Using premium in a car that says regular will do nothing for you. I doubt you’d see much difference either way.
    #4 true. properly inflated tires = less rolling resistance.
    #5 Ac will always use gas, but VS windows down? Depends on speed. I wouldn’t be doing highway speeds with the windows down to save gas.
    #6 almost all that stuff is BS. However at low temperatures synthetic lubricants can provide a boost to your fuel economy. Particularly on short trips. They tend to be much more stable in viscosity than dino oil.

  88. milw123 says:

    Tip #7.5 Pump and run! Easiest way to stretch your fuel dollars is to not spend them in the first place!

  89. @Geekybiker: #2 true, even if its not a lot. What a lot of BS about the fuel air mixture. Its about pumping losses.

    Thanks, I’d missed that one. According to their logic, a filter that is 100% blocked would give you twice the mileage you normally get. Of course, changing your air filter twice a year may be a net dollar loss, but you’ll get better day-to-day mileage.

    An exception….if you are driving in the mountains in a non-turbocharged car that was built within the past ten years or so, you have a high likelihood of getting better mileage above 4000 feet, given a relatively level road. The fuel/air mixture will be leaned out because of the thinner air, (less air moving past the air mass/hot wire sensor) and as long as you don’t leadfoot it, you’ll get much better mileage at altitude than at the same speed than at sea level – and the lower air resistance because of the thinner air doesn’t hurt either.

  90. TreyWaters says:

    @CaliforniaCajun: I understand that. I was simply stating that the generalization that using premium over regular nets no benefits is incorrect.

    Also, if you noticed, I was responding to someone that questioned whether the added cost of premium offset the difference premium made wrt mileage.

    Common sense should dictate that you use what your car’s manufacturer recommends.

  91. elephantattack says:

    @HIV 2 Elway: Also, I get a kick out of the Missoura rednecks who write letters to the editor bitching about gas prices and then pass people on the right shoulder in excess of 90 mph.

    I live in Missouri… this is the truth… Ironically, I’M the one who gets the ticket too! I can’t STAND it!

  92. Fortain says:

    @Balisong: @Balisong:

    50 mph, actually. Any slower, and the windows are better; faster, and the AC’s better.

  93. Aesteval says:

    @AaronZ: Changing an air filter is one of
    the best things you can do to get better mileage as it’s an easy 10%
    gain in efficiency over a clogged filter (quite possibly a very clogged
    filter, and also may be skewed towards older cars.) Assume 27 mpg on
    clogged filter, 30 mpg on new filter, and a 10 gallon tank. That would
    equate to 270 miles vs. 300 miles on one tank. Assuming $3.50 per
    gallon, that’s essentially two fill ups before you make the money back
    on the filter. The better question on the filter comes down to is when
    should it be changed; does it need to be changed as frequently as
    recommended…probably not. The thing is that no matter what the
    initial cost, so long as it last over a long enough period of time the
    savings will indeed add up. You just want to make sure you don’t
    perform these changes before it’s actually needed to do so.

  94. STrRedWolf says:

    Mythbusters actually took many of these myths on… and from the summary, I have to doubt them myself.

    #1 can be safely busted because regulations require fuel to be within a tight range of the ambient temperature. That was described here on the Consumerist.

    #2 I have my doubts, because there will be a time in which the computers can’t adjust any more… and that older cars don’t have such a computer in their systems. Checking the air filter will help.

    #3 you really need to read the article for, because there’s a caveat: If your owners manual says “YOU NEED PREMIUM” then you have to pay the $4-$5 a gal stuff. Usually, though, that’s for high-end super/hypercars like Lambo’s or 911’s.

    #4 is just repeated advise.

    #5 The mythbusters actually did this one (among other milage tests). I forget the result, but there was a substantial increase in milage from one to another. The best however is in the article: “The best choice – if temperature and humidity allow – is to keep the windows rolled up and to turn the A/C compressor off. You can keep the fans running to blow in air from the outside, but your car will be as aerodynamic as possible while still letting you breathe. You will save gas, but the fuel economy improvement will be slight.”

    #6 Bolt-ons/Pour-ins/etc.

    The mythbusters also looked at that — and flunked every one.

  95. planetdaddy says:

    Here is how I have saved gas.

    1. I have just cut down on my driving.
    2. I also share a car with my wife so I am only filling up one vehicle.

  96. Grive says:

    @jasezero: Mainly because it’s talking about MYTHS, not about facts regarding fuel efficiency.
    @Ash78: The TDI forum guys are correct. Every time you use the brakes, it means you overused fuel in keeping a speed too high for the road. You’d get top fuel efficiency if you were to drive at whatever speed and then simply stop accelerating, keeping the car in a high gear, so it rolled to a stop where you want to stop. Of course, this is impossible in a lot of cases, but the less you brake, the more you save on fuel.

    Of course, this doesn’t mean drive like a madman… just predict future road conditions (i.e. if you see a stop sign in the next block, stop accelerating as soon as it’s safe).
    @Steaming Pile: No, don’t set cruise control.

    CC = wasting gas, and a lot of it, unless you drive in long straights with no height differences. Cruise control is only for convenience.

    Knowing how to modulate your speed for top efficiency will always be better. If someone can’t do this, then yes, CC would help, but in this case, frankly, that person should first learn to use the pedals well before worrying about gas efficiency.

  97. dazzlezak says:

    I also call BS on the air filter!

    I replaced regular air filters with a K&N air filter. and immediately noticed a 10-15% gain in mileage on my Mazda Protoge LX 1.6L engine.

    Better breathing = better gas mileage and better horsepower

    (everything else is totally stock)

  98. cerbie says:

    #2. Do some Googling. It’s surprising how clean FRAMs look after X miles compared to the competition. Not having the money for K&N ($50+), I’ll stick with Mann ($6-10). Ditto on oil filters.

    Now, if you have an air filter that’s supposed to be good for ~30kMi and you are replacing it every oil change, you are wasting money, for sure.

    #3. True for me. My car runs like crap on any 87. it is taking Shell 89 OK (how “OK” is will be seen next time I have to make a left turn onto a highway), but it doesn’t quite have the power of 91 (NA B230F, so every HP and 1 FtLb counts!)…but not a bit of MPG difference. Flame trap cleaning got me 2MPG, but not premium fuel. I wouldn’t be surprised if there were a difference in mostly city driving (I do about 2/3 highway), or in other cars, though.

    #5. I gained 4 MPG since starting to drive my car, and have switched air on. I need A/C, and it hasn’t worked out bad. About 2 MPG from changing my route to work, and about 2 from PCV screen.

    #6. I’ve yet to buy a fuel additive over the internet, or, as is often spoken of, through a MLM scheme. I also haven’t noticed a MPG increase, either. Just more power, smoother idling, and better cold starting.

    I get 25MPG (EPA 18/23 w/auto, and if I can do 21, I’m sure 18 isn’t hard) by not rapidly accelerating unless turning left into 40+MPH traffic (I hate doing that), keeping distance from other cars, coasting whenever possible, working to maintain speed, braking as lightly and soon as possible, should it appear coasting won’t do (I get through about 1/5 red lights w/o stopping this way, now), and letting aggressive drivers do whatever the hell they want around me, because getting a car-length ahead is just not important to me.

    I hope folks who got manuals before gas prices spiked up are feeling smug, now. They deserve to.

    @homerjay: I actually laughed.

    @t325: Doesn’t that depend on the specific car/engine/transmission combo?

    @AustinTXProgrammer: So, let’s say you have three scenarios:
    A. 60MPH, see a long green, stay 60MPH, brake when you must.
    B. 60MPH, see a long green, let the car slow down as it will, braking maybe the last 20MPH.
    C. Like B, but with a car that is nearly fully computer controlled, and will shut off fuel.
    C will get you the best MPG, B will get slightly better (but possibly a negligible amount), and A will get the worst.

  99. Grive says:

    @AustinTXProgrammer: While you’re technically correct (partially, at least), you will note an increase in fuel efficiency by engine braking, because of a very simple fact: You’re using a longer distance to brake.

    If you keep up a mile at 60mph (let’s asume you do 1 mpg here for simplicity’s sake), and then brake, you used up 1 gallon to do this. Now, if you do half a mile at 1mpg and engine brake at a nearly infinite amount of mpg (in newer cars, engine braking = almost zero fuel consumption) for half a mile, then you will have used 0.5 gallons to cover the same mile and slow down.

    So that’s some fuel saved, taking into account that previous to this mile (basically, the acceleration phase) both cars had used up the same amount of fuel.

  100. wesrubix says:

    @Nighthawke: Thank you. I get so frustrated at misrepresented engineering information.

    Also make sure you are using at least your minimum octane in your engine! I don’t think 5-10 cents/gallon is worth a case of the knocks and potentially damaging your engine altogether!

  101. Oshawapilot says:

    Allot of truth in there, but it seems that they forgot the most obvious thing – stop driving like a twit. It never fails to amaze me all the people that drive like they’re in a race (jackrabbit driving from red light to red light, agressive lane changing to gain that extra 10 feet, driving at 80MPH) and then have the gall to complain to no end when it comes to the resultant MPG they’re getting.

    Slow down, drive economically, and you’ll get better MPG. If your too impatient to make an effort, then you have no bloody excuse to complain about your low fuel milage.

    Last, I’ll agree that this article is way off base with the premium fuel issue – if your car REQUIRES premium (supercharged, turbocharged, or otherwise high compression) you can almost count on worse fuel milage by trying to use lowtest gas. My last car was supercharged and it ran *terrible* on 87 octane – it’d run on it, but the computer retarded the timing so much (to avoid engine damage from detonation) that you had to use about 25% more throttle to gain the same amount of power. In the end this resulted in much worse milage, and vastly less horsepower.

    If you can’t afford to put premium fuel in a car that requires it, consider another car, don’t just think your going to get off easy and buy the cheap stuff, because chances are you’re only screwing yourself.

  102. Ragman says:

    @cerbie: Where do you shop – or, what do you drive??? K&N air filters are <$50 online(for OEM replacement, not the fancy ones), and all my airfilters have run $12-15 each for Hondas and Saturns. The only <$10 filters I’ve seen were for cars built 20 years ago. Not to mention most air filter changes are recommended at 12-15k miles or one year.

    On octane ratings, definitely RTFM – you might be surprised that your car may need 89 octane. It’s not just the Ferraris and Lambs that need higher octane. My motorcycle runs on 89 minimum, and it’s not a racing bike. You also need to pay attention at the pump. Many cars need 87 minimum, even the smaller, cheaper ones. That means, if you’re off the beaten path, you may have to buy mid-grade, since many gas stations off of major highways will have 86 regular, while stations in well traveled areas have 87 regular. I noticed that on a motorcycle trip down old 2-lane highways in west Texas, where the Premium was 90 octane, while it was 92/93 octane at the same chain on I-35.

  103. gerardrj says:

    Please stop perpetrating the myth of high octane and performance!

    Octane rating has nothing to do with the amount of energy in the fuel!
    A higher octane rating does not provide better horsepower, torque or fuel milage.

    Octane rating does not affect engine performance unless you use a fuel that has an inappropriately low rating compared to the requirements of vehicle you are putting the fuel in. Putting 91 octane in a vehicle that only requires 87 will get you nothing except poorer. Conversely, put a 50 octane fuel in any gasoline engine and watch the engine self destruct… quickly.

    Octane rating is a measure of the “anti-knock” properties of the fuel. A low-compression engine can get away with low octane, but higher performance engines run at higher compression ratios and might/will cause auto-ignition of the fuel-air mixture before the spark plug fires at an appropriate time/angle. This pre-ignition causes lower fuel milage, excess noise, loss of power and possibly engine damage if the effect is severe enough.

    If you are driving an “average american sedan” then an 89 rated fuel will usually work fine in your engine. If you are driving a Ferrari and try using 89 octane it might work well under light engine loads, but step on the throttle and watch the engine self destruct.

    Diesel fuel’s octane rating equivalent is usually in the teens (15-20 rating but diesel is rated by cetane). The difference is that gasoline cars put a fuel air mixture in the cylinder then compress it and spark to ignite. In a diesel you first compress the cylinder then inject the fuel and allow it to spontaneously ignite, just what you don’t want in a gasoline engine.

  104. cerbie says:

    ’93 Volvo 240. 4 years to go to 20. I wouldn’t say no to a 940, but that opportunity came after I was broke from buying this :).

    I shop wherever, depending on what I need (sometimes, the extra at the dealer isn’t so bad…sometimes, it’s insane). Advanced just got what I thought was going to be this week’s spending cash, earlier today, over three trips.

    The first two here have pretty good prices (no idea if they’re decent; just from Googling). I have yet to see a cheap K&N for these cars. OTOH, even the dealer isn’t a real rip for filters and such, so there might just not be a need.
    [www.ipdusa.com] (I shop here, too, but they are pricey on some things)

  105. stands2reason says:

    …Premium fuel costs more and contains less energy densite. Who would be stupid enough to use it?

  106. gerardrj says:


    You don’t get it. The computer is not retarding the timing based on octane, the fuel is simply burning spontaneously before the spark plug fires and robbing you of the power and causing premature engine wear/failure.

    This is supremely bad.

  107. Grive says:

    @stands2reason: Someone who likes performance out of his car more than an extra few dollars, like me.

    While it has less energy “densite”, it does allow for a considerably higher compression ratio. My car is running well over 100hp per liter. “Regular” fuel would be considerably more expensive for me, because a) the engine would need to adjust and start working under suboptimal conditions, and b) I’d need a new engine if I decided to rev it up.

  108. Grive says:

    @gerardrj: Some computers can allow for suboptimal fuel by changing the injection.