Here's the question. Reg E10 87 oct gas at $2.85 a gal right now. MPG on road trips with reg E10 gas = 48 calculated. Premium 91 oct straight gas "no ethanol" at $ 3.20 gal. What mpg would i need to get to make it worth trying a tank of the 91 oct no ethanol? Is it even possible to increase it?
Well to get the same ratio you would need 53.89 mpg. Will you get than going to 91??? I have no idea and doubt it is worth it.
The price difference is 12%, so you'd need to see 54mpg or better to make it worthwhile. But does mileage increase with premium? I seem to recall that it doesn't, at least with the iconic version. If I'm wrong, I'm sure someone will correct me.
Is premium gas 'ethanol free'? I didn't think so. You won't get better gas mileage from the premium chemistry, but if it is actually ethanol free, you might get 4-5% better mileage according to what I've read. Still not cost-effective.
I have been assuming that the Prius ECU treats ethanol as filler. For most cars 10% ethanol should result in 3% less mileage In the Prius it seems more like 10% less mileage To make Premium 'worth it' you need over 12% better mileage 12% more than 48 MPG is 53.895 MPG
You'll probably get a bigger increase by inflating your tires to max. sidewall pressure and when it is cold blocking the grill.
First, Ethanol is not a filler. It just contains 30% less energy than gasoline so E10 loses about 3%. Second, you will actually get slightly poorer MPG with Premium assuming the same ethanol content. So using Ethanol-free 91 octane will not quite make up for it's cost differential. JeffD
