Re: Anyone Here Use Fuel Additives ?
There is a hell of a lot more that plays into octane than simply what the owners manual says. High temperature, heavy load, (towing), density altitude, all play into it.
Perhaps in most cases 89 octane will work satisfactorily in a 5.7 HEMI. But there are too many variables. My car operates in very high temperatures. That alone can cause knocking and lack of performance. While 91 may or may not be necessary in Fargo in January, it may very well be in Phoenix in June.
I would like to know what has changed in the engine itself, that dropped the octane call out from 91 to 89? Other than the desire for Jeep's customers to be able to burn cheaper fuel. In any event, I'll play it safe and run 91 in my G.C. I'll save the few lousy pennies somewhere else.