Might sound dumb but I seem to get less milage when I use premium. 87 has always worked for me. I just make sure I go to stations that are always busy. Keeps from old crap filled gas getting in my tank.

 

Unless you have your JK tuned for 91, that makes complete sense.



As for cheap gas, just know the octane has nothing to do with how "cheap" gas is. Where you buy it does. Shell or other quality 87 octanes fuels are clean. It's a misconception that 87 or 89 gas is "dirty".

 

Thanks for the advice.. I guess I get to paranoid about things .. I'll just spend the extra cash and use 91 lol. Just incase .. But a 76 near my house has 100 octane lol.. U think it will mess up the engine? I'm not gonna try it btw

 

Won't mess it up. But your engine def isn't 'tuned' for it.

 

Waste to use anything but 87. Don't fall for marketing.

 

For the record - I have tested with 87 and 91 and found that the difference in mileage gain does not merit the difference in the price. i have noticed a difference running Shell or BP 87 as opposed to the local fill up spot. Same price, more miles... (This was hand calculated with daily drive commute so there is some consistency.)

 

You get a mileage gain when running premium? That's somewhat odd... I'd expect it to remain the same, if not drop. Unless you're running a 91 octane engine tune, that is. Then a gain would make sense.

I have noticed that I get slightly better gas mileage when running name-brand fuels. My guess is that the cheap fuels have a higher percentage of ethanol in them.

 

We have 93 octane here in St Louis, and I went from 18mpg average on 87 octane to 15 mpg on 93 octane (all Quik Trip gasoline)

 

Wow I would think it would be better to use 93

 

It won't. It will get worse. You MUST advance the ignition timing to account for the slower burn rate of higher octane gasoline. This is only done with a custom tune/flash tuner.