My guess is that you've wasted it. Higher octane fuel is less susceptible to detonation problems. I'm not positive about the 6cyl, but the 4cyl specifies to use 89 octane fuel in the owner's manual. Using anything higher than that is essentially a waste of money. Funny, cuz they actually say that in the owner's manual, they say that you will get no performance benefit from higher octane fuel and will pay more for nothing.
For a stock 4cyl, at least, you are wasting money using higher octane fuel. Start boosting the compression or adding FI systems and you just may need that higher octane rating.
Again, I'm not sure on a 6cyl, but check your owner's manual. If it says to use 89, then I see no real reason to use any higher unless you'd put certain mods on.
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