Re: 89+. Octane?
People think that higher octane gas is "better, more powerful". Not really true per se.
Here's the deal in simple terms. The higher the octane number the HARDER the fuel is to ignite - that is, you can compress it more without it "dieseling", or igniting due to simple compression. That's why higher octane fuel MUST be run in "performance" engines - ones that have higher compression ratios. The higher octane fuel does produce more power, but only because it is compressed more before the ignition system in the engine ignites it.
As stated above, unless your engine is of higher compression there is no benefit to running higher octane gasoline, but there is probably no harm. However, if your engine has been "hot-rodded" and does run at higher compression, then running too low of an octane number fuel WILL cause "dieseling" (detonation) and pinging, which is harmful to the engine.
Years ago I used to have a car that ran on "high-test" gas. When I needed gas for my old Cub Cadet lawn tractor I would just throw the can in the trunk, and when I'd fill the car I'd fill the tractor can. One day I was BSing with the guy that ran the tractor parts place and I mentioned what I was doing to him. He told me to run only the "low grade" gas in my Cub Cadet. So I switched, and you know what? The Cub Cadet started easier and seemed to run better on the cheap grade of gas.
Short answer: Follow the manufacturer's recommendation.
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