what’s the difference between gas grades, i.e. 87, 88 “the new standard” and flex fuel?


So, I have a 2012 Ford focus, and always get 87 grade regular, even though flex and or 88 are supposed to be good in 2001 and newer vehicles right? Should I be saving myself some money or keep buying regular?

In: Chemistry

88 octane won’t do any harm, but it won’t gain you anything either.

Read the owner’s manual, if it says flex fuel is ok, then you can use that. Expect worse mileage on E85 gas though.

Higher octane means it can be compressed more before self-igniting. However compression ratio is something designed into the engine, if you don’t have a high compression ratio, you don’t get any benefit from the higher octane. If you do have a high compression ratio, using low octane fuel can cause knocking.

E85 is 85% ethanol, and will not work in normal gas engines. This is what the flex fuel thing is for.

Most places have 10% ethanol, which will work in normal engines, but if you have an old car, or a car you rarely drive, it’s better to use ethanol free gasoline, because ethanol absorbs water, which can make it corrosive, or just not burn as well.

The grade refers to the octane rating of the fuel, which is a measure of how easy it is to ignite.

The harder a fuel is to ignite, the more it can be compressed in the engine first, and the more energy it will release.

The thing is that an engine has to be designed to work with a higher octane fuel – if you put the wrong octane fuel in a car, it will not be igniting at the correct points in the engines cycle, and will work poorly (in some cases causing damage to the engine).

Check your manufacturers information for your car, which should tell you the octane ratings the engine will work best with.

If you do end up putting the wrong grade in your car, it isn’t the end of the world – the car will run on a range of octane ratings, it just won’t work as efficiently, and may increase wear.