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QotD: Gas Quality

Question: What kind of gas do you put in your car?

My Answer: The Touareg gets the premium stuff. I don't doubt that it's barely better than the non-premium stuff, but it's peace of mind for an expensive (relatively) car. So pfffft. The Aztek gets 87 or the lower-grade stuff largely because it's what the manual actually recommends.

You are encouraged to answer the Question of the Day for yourself in the comments or on your blog.

11 Responses to "QotD: Gas Quality"

  1. apparently (per my Audi dealer) the onboard computer will actually compensate for the lower octane fuel to reduce engine knock.

    the lower octane fuel may work without noticable effects but will reduce your mileage.

    my brother in law switched from regular to premium gas in an A4 Avant and his mileage went up by close to 20%. ymmv.

  2. YMMV, ha ha ha. Literally!

  3. My 1.8T Jetta only gets premium name-brand (Exxon, Texaco, BP) gas. I've tried cheaper stuff (like BJ's & Citgo) and I've tried non-premium (low-grade, not mid-grade) and it really makes a difference. My Jetta performs so poorly on cheaper go-go juice that it's not worth the "savings" - after all, what good is a turbo if you can't have fun with it? 😀

  4. OMG, it's people like all of the above (so far) who help oil companies make record profits. Some things to keep in mind:All newer cars produced over the past several (at least 5-10 years) will, as kdf points out, automatically adjust the timing of your engine to compensate for a lower octane.All mass production, gasoline powered cars sold in the US will run perfectly fine on regular, unleaded fuel.The reason some car's user manuals state that you should use premium grade gasoline is because the manufacturer had the car EPA tested using premium in order to get slightly better results; and are therefore required to recommend using premium gasoline.In general, only a car with a pretty high compression ratio (e.g. 10-10.5+:1) would ever need a higher octane gasoline, and even then, see above about the automatic adjustment of your timing. The vast majority of cars manufactured today do not have engines with compression ratios that high, and even those that do, see above about automatically adjusting the timing.The only time a computer-controlled, high compression engine is going to see a noticeable benefit from the higher octane gasoline is under extreme driving conditions, e.g. accelerating up a reasonably steep hill or attempting to go the top speed of the car. In those cases, you might hear some pinging or eek out an extra few MPH at the top end.The amount of net energy (as far as your car is concerned) in a higher octane gasoline is actually less than the lower grade. Therefore, all other things being equal, you should actually get slightly worse mileage from a higher octane gasoline. But the difference is quite small and probably difficult to measure without rigid controls on all the variables.Most gasoline stations in a given geographic area get their gasoline from the same refineries. The only difference might be some "secret formula" that one company squirts in vs. another company's "secret formula". But, in general, the gasoline in you particular area is probably coming from the same refinery/refineries (depending on your geographic area).The people above, or anyone else interested, who speak about increased mileage or really any noticeable effects from using premium vs. regular gasoline should perform the following experiment. Drive your car to near empty. Then have someone else go and fill it up with either regular or premium (or non-name-brand vs. name-brand gasoline). That person should keep a record of what they put in, but not tell or even hint to you what they put in. Ideally, you want to do this over a period of several tankfulls, driving it to near empty each time. You, as the driver, should keep track of your mileage and any other perceptions. Likely, you won't notice any difference, except for the extra 10-20 cents per gallon you end up saving.

    My guess is that the above mentioned perceptions (increased fuel economy or whatever) are a psychological effect and/or coincidence. That is, the driver who said they got 20% better mileage happened to do a lot of city driving the week they had the lower octane gasoline, or they were sub-consciously wishing to justify their expectation that premium gasoline really is better and were a leadfoot with the lower octane tank and driving more normally with the premium, but without even realizing it.

    Happy experimenting!

  5. My 2004 Toyota Corolla gets regular only. Most cars are designed to use regular fuel, and using premium has no effect.

  6. My supra only gets Premium, and generally only Shell.

    There is a VERY noticeable difference between using low and high octane, in terms of performance and emissions, and my engine was DESIGNED to run premium. My old audi 5000 CSTQ just gets medium, and from most any reputable names. (never 7-11)

    in response to Rob, Adjusting the timing (and Air Fuel ratio, etc.) to compensate for lower octane gas results in less horsepower, and less efficiency. To claim that is "compensates" so well that there is no difference between running one octane level over another is nonsensical. the engine is COMPENSATING. thermodynamics 101... energy does not come from nowhere, and compensation will always result in a loss of energy. If engines could "compensate" for lower octane fuels with no loss of energy, then we'd have extremely low octane fuels.
    "Most gasoline stations in a given geographic area get their gasoline from the same refineries. The only difference might be some "secret formula" that one company squirts in..."
    ...that's not only untrue, it's irrelevant. Many times the most significant difference between different stations in the same region is the quality of their tanks. The quality of the gas relies heavily on solid tanks which do not allow contaminants, such as water. there is a MEASURABLE amount of water in gasoline that varies depending on who's tank it came from, and in general, Shell has very clean gas, while 7-11 has a much higher percent of contaminants.

    Using gas with the octane level that the engine was designed for will increase your efficiency, your power, reduce emissions, and increase the longevity of your engine. (Not using higher octane alone, but specifically using what the engine is DESIGNED to use.) Engines are built with incredibly small mechanical tolerances, but are built to "get by" in un-ideal situations. ...But if you plan on KEEPING the car for more than a couple years, i'd suggest using CLEAN gas with the octane level the engine was designed to use, using the oil-weight it was designed for with regular oil-changes, using the coolant the engine was designed to use, etc. Sure you could get by with old dirty oil never changing it, and water instead of coolant, and the incorrect octane, but you think that'll last as long or work as well? if so, what the hell are engineers paid for?


  7. By the way, rob, i HAVE experimented with gasoline in blind studies, not just using my own perception to gauge the effect, but emission sniffers, Dynos, etc.

    I will concede that in a 2001 Dodge Neon, you can absolutely (and probably SHOULD) run low octane, and would definitely see NO benefit from increasing the octane... but when i'm driving my Supra, pushing 14PSI of boost at 5,400RPM, in a Straight 6 cylinder turbocharged 3.0 liter engine designed to burn premium... you'd better believe i'm not running 87 grade from 7-11.'s all about what the engine was designed for.

  8. Rob, I'm also helping Audi to record profits 🙂

    I would disagree that 'All mass production, gasoline powered cars sold in the US' can run fine on regular fuel. I would give you about 80% but to compare a high performance vehicle (say a 2006 Audi A3 3.2) with Jeff's 2001 Dodge Neon would be a stretch.

    I do agree with your point that all fuel does come from the same refineries. I used to work for Petro-Canada in their distribution center and for all the service stations in our city, all fuel came from either Shell or Esso. You are also correct that the only difference was the additives that were added to the fuel. I do think that the additive makes a difference and would choose a name brand over something like 7-11, especially in the winter.

    As for water or impurities in the fuel, any gas station could end up with either regardless of whether it was a 7-11 or a Shell station. It has more to do with age of the tanks and the level of corrosion. It also depends on the vigilance of the station owner as when they check the inventory levels of the tanks there is a paste that they put on the dip sticks that indicates water. Some owners are better than others.

    One station lost over 60,000 liters of fuel over the course of several winter months because they were incompentant and didn't notice the lost fuel in their record books. Thankfully, due to winter and a heavy clay soil base, most of the fuel was recovered.

  9. Rob is correct with respect to all stations getting the same gasoline. The only differences are the additives. But, it is important to note that these additives can be quite good for your car. For instance, Chevron's Techron has been tested to be the best engine cleaning formula among the major companies. These additives may also add some performance, mileage, and/or emissions improvements, depending on the mixture. Most, if not all, of the U.S. car manufacturers test their cars with Chevron/Techron for these get better scores on mileage and emissions.

  10. Indeed, fuel additives do make a difference. Several auto manufacturers got together to form a standard defining what they deem to be the optimum fuel. The site tells which retailers sell gas meeting that standard. It's an interesting topic - check the site out.

  11. Hey guys, i would like to thank you for having this convo so i could find out if i should run high octane fuel in my supra. and it worked!