What grade of fuel is used when testing MPG on cars&trucks?

The dealer said that the car Im looking at buying gets 40mpg, but a website says otherwise.

I was wondering if the dealer tested with Premium gas? Or if they tested with mid-grade or regular to get the numbers that they have.

8 Answers

  • 1 decade ago
    Best answer

    It all depends on driving habits, weight and such, not type of fuel. A website probably used a 500lb person driving it, and then in actual drivng senarios as well. Who knows what their test conditions were. And besides, the dealer's mileage quote, is Estimate EPA mileage. Which can be less than posted.

  • 1 decade ago

    Gas mileage is determined by several factors, but the grade of gas is determined by engine compression ratio. The owners manual will state the octane level required for that particular engine it will also tell you what the compression ratio is for the engine under specifications. What some people do not know though is that engine compression and gas mileage go hand in hand. The higher the compression ratio the better the mileage but the higher the octane required, the same is also true for the reverse. Another thing that is not publicly known is the gas mileage listed on the stickers at the dealership is exaggerated, upward of 4 to 5 miles a gallon. The fuel used in testing the cars mpg is the recommended fuel for the car. The mileage is actually a calculated guess rather than an actual road test.

  • 1 decade ago

    First, the dealer doesn't test for MPG. That is done by the Federal government, and is done according to a very sophisticated and convoluted testing requirement (commonly referred to the FTP, or Federal Testing Protocol).

    The likelyhood of ANYone ever driving according to this procedure is VERY slim.

    The reason for it is so that there is a platform that EVERY vehicle does exactly the same thing, and therefore there is a basis for real comparison.

    The FTP is used for a whole host of data, but the primary focus is both emissions and fuel economy.

    As fo the fuel grade, the ONLY difference between 87 octane and 92 octane has nothing to do with the energy stored in the fuel. It has ONLY to do with the anti-knock compounds.

    Cars that require the premium (Porsche, Cadillac, BMW, etc) are designed for the more expensive fuel, and their ignition timing is programmed for the added anti-knock additives.

    If you are driving a car that only requires 87 octane, using the more expensive 92 octane is merely a waste of money, and you will see no appreciable improvement in either economy or performance.

    Source(s): ASE Tech
  • 1 decade ago

    Actually most cars are tested for emissions and drive cycled for gas mileage with Edeline instead of unleaded pump gas. Approx 90 octane and more stable than gasoline with additives and now ethanol. What I can tell you with test fuel in a Mercedes Benz 5.0 L engine 500SL the car really will go! So fuel is a contributing factor as is a feather or egg pushing down the throttle. Smoothness and accelerate nice and easy make the best mileage as does correct air pressure in the tires and UN damaged body work and plastic parts still under the engine and rear body work. Besides the window sticker says mileage estimate your mileage may vary. MY 6.0 L 2006 GTO 6 speed manual sticker said 17 city and 24 highway And by setting the cruse control at lower than 70 miles an hour with recommended tire pressures getting into high gear fast.I Got 27 mpg. so those are just estimated figures.

    Source(s): 30 year auto tech
  • What do you think of the answers? You can sign in to give your opinion on the answer.
  • 1 decade ago

    The dealer didn't actually test the car's mileage. Think about it - do they have time to drive every car they get for three full tanks and take an average? They are throwing a number at you to try and get you to buy the car...hard to believe, I know. Go to http://www.fueleconomy.gov for fuel economy estimates obtained from laboratory tests conducted by manufacturers according to federal regulations.

  • 1 decade ago

    tkh24 said most of it. High octane is only important in high performance cars. Higher octane does not produce more horsepower, nor does it make the car go farther on a gallon of gas. It does prevent detonation (pinging) in high compression engines. This is why most supercharged (turbo or blower) cars require 91 or so octane fuel.

  • 1 decade ago

    whenever i am buying a new car i guess it will be 5-10 mpg less, cuz it is never right, but I am not sure what type of fuel, i would think whatever is reccomennded for that vehicle, some of them run better on the recomended cuz their computers are set to that

  • gary o
    Lv 7
    1 decade ago

    The std. test is run under ideal conditions with the recommend fuel for that particular vehicle. They are only guide lines and individuals may not get what is advertised.

Still have questions? Get answers by asking now.