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lucky4075 07-16-2012 04:57 PM

91 octane
Im not sure if this has been answered before but:

Would there be any long term effects or damage from running 91 octane as opposed to the 87 the owners manual says? I ask because the local gas station has ethanol free 91 now, and its really about the principle of putting pure gas into my tank for me. A mechanic that I trust very much said that it would be fine and that the owners manual says 87 because thats just the minimum you should ever put in there. I'm still a bit skeptical tho.


brendend 07-16-2012 05:04 PM

Higher is fine just don't go lower

schnutzy 07-16-2012 05:10 PM


Originally Posted by brendend (Post 2590164)
Higher is fine just don't go lower

not quite.
running higher then recommended octane is not just fine.
the 91 does not burn off as well in a motor designed to run on 87. as a result, it burns dirtier, and can cause carbon build up. that build up leads to a poor running engine, pinging, and all that fun stuff.

Jerry Bransford 07-16-2012 05:57 PM

Higher octane is NOT fine. The higher the octane level, the harder the gasoline is to ignite and the slower it burns and the less well your engine will run with it. Not to mention higher octane level gasolines can leave more deposits behind since it doesn't burn as quickly or as easily as lower octanes do. The ONLY engines that can take advantage of higher amounts of octane are those that were designed for it with extra-high compression levels or who have excessive carbon deposits that raise the compression level which can make an engine ping.

What does octane do? The first thing it does NOT have or add is more power. Octane's SOLE purpose is to slow down/retard how easily the gasoline is ignited and reduce how easily it can be ignited prematurely from excessive compresson... which is why only higher compression engines require and benefit from higher levels of octane.

zomby 07-16-2012 07:16 PM

here is some other info don't mix ethanol fuel with non ethanol fuel when that originally switched the mbte with e 10 the marine and small engine industry was in a panic with jelling in fuel tanks lines and in the carburetors. the stuff is nasty and still happens if you leave e 10 in stuff that is vented to the open atmosphere to long, if its vented to the open fuel is only good for no more then 3 weeks, it stinks and i hate having to clean it but i guess its my job and what id do

lucky4075 07-16-2012 09:27 PM

Yeah I'll stick to the regular 87 even though it has the crap in it. My gut thought it was a bad idea because of the slower/less complete burning etc.

I have mixed ethanol gas and pure gas before, all it would do is dilute it to almost no ethanol depending on how much pure gas you put in. When I do get the opportunity to get to the station near here that has pure 87 I usually wait until the jeep is below 1/4 tank.

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