Is premium gas suitable?

Toyota's tech training document advises against use of premium gasoline. If you wish to verify, go to autoshop101.com, select the Technical Articles link, find the Hybrid13 Fuel and EVAP System file, and look at page 3-4.

 

No Prius user finds better mileage via higher Octane gas.
Some do find higher Horsepower.(going uphill over 85 at full throttle)

Some companies sell 0% ethanol Premium while selling 10% ethanol regular, but the Mileage improvement is due to less ethanol, not more Octane.

Toyota pretty consistently advises 87 octane as being ideal. (there was one typo of 88, and in the mountain west they use 85)

 

More octane does not equal more power. It only means more "anti-knock" compound. This keeps those high-compression "performance" cars from making a lot of noise. Otherwise, it is the same gas. Save your money.

 

What probably fuels this confusion, if I may use that metaphor, is that in some areas premium gas is ethanol free, where regular gas isn't. In that case the premium gas produces better mileage, not because it is premium, but because it doesn't have ethanol.

Tom

 

Gasoline formulation is often misunderstood. Let me explain. Gasoline, a chain of hydrogen and carbon atoms (hydrocarbon), contains heptane and octane. Heptane (a 7 carbon molecule) is far more volatile and undergoes combustion very easily under compression compared to octane (a 8 carbon molecule). Gasoline formulated entirely of heptane would have an octane rating of 0 and vice-versa. The reason why you lose performance in high compression (performance) engines in low octane (high heptane) gasoline is the heptane causes the fuel air mixture to combust during the compression stroke as apposed to the combustion stroke. Hence lost power and the "knock" you hear.

For the Prius this is not a problem because it emulates the Atkinson cycle by holding the intake valve open longer during the compression stroke to gain higher efficiency at the expense of power.

 

I've got the same dilemma here Petsitter. They are "phasing out" regular (ethanol free) petrol, so soon I'll only have the choice of either E10 or premium. For the time being I can still get regular (ethanol free) but in the future it's likely to become hard to find.

I used premium once and I had no problems with it. The fuel consumption however was pretty much the same as with regular, might have been a tiny bit better but the difference was too small to reliably measure in one tankful. So kind of a waste of money considering it cost about 12% more.

I'm still not 100% sure what I'm going to do when I no longer have the option of ethanol free regular. I'll probably just have to go with E10 (10% ethanol) since a 3% to 4% drop in MPG is preferable to a 12% increase in price.

 

Be happy. The engine will be getting a continuous dose of injector and valve cleaner.