Contrary to popular belief more octane doesn't make your engine perform better nor is the gasoline any cleaner than lower octane ratings. Octane is a burn retardant, that means that it slows down the rate of combustion (burning) for gasoline. Octane ratings higher than those required by your engine actually decrease performance, albeit very slightly and probably imperceptively at that, so buying higher octane ratings than needed just wastes money. As engines wear and tire out you may need a higher octane rating to control detonation, my last car wouldn't climb the mountains on 87 after about 100,000 miles and needed 89 - 91 to keep from pinging, but around town it did just fine on 87 octane up until I had it rebuilt at 195,000 miles.
I am not reccomending violating your owner's manual requirements, if your owners manual says to use mid grade or high test then by all means do it, don't jeopordize your warranty to save a few cents per gallon, but if you're adding high test because you think it is better gas and your manual doesn't suggest or require it, then you should revisit this logic.
by bates on January 04 2009
this tip works for 86% of voting Fuelly members.