I’d like to see data from this decade that proves engines run “cleaner and cooler” on higher octane fuel. They also only started certifying top tier fuel in 2004. So your 40 year old anecdotal evidence may need to be revised. But if you want to live on 80’s information you can do that.
I’d also argue that since you care enough about your engines to run 91 octane you also maintain them pretty well. I’d wonder if all your engines would still be running just fine if the only variable you changed was octane?
I think we can both agree that running top tier certified fuel is the way to go though, even if we can’t agree on octane.
Also, yeah GM recommends premium. It doesn’t require premium. I have a Toyota with a 2ZZ-GE engine that has a 13.5 to 1 compression ratio. That REQUIRES premium.
Well before "Top Tier", only the high octane offerings had the premium additives. If I drove any vehicle for a length of time I would compare gas mileage using low octane and high octane gas, especially when racing. Still do it today, though it's far more detailed in Excel. If you want to see a dramatic example of your vehicle running cleaner and cooler with a more smooth idle, run a tank or two of 100-104 octane unleaded in it from Sunoco. You can do the same with E85, it takes about 5 full tanks for the computer to fully adjust to it.
Down here in Florida this is what happens when a man runs 87 in his high compression Gen IV 6.2 engine. Every time he takes off from a traffic light his engine the engine pings and timing is retarded. When he goes to pass a slowpoke, the engine pings or knocks and timing is reduced. This is not always audible as these modern vehicles are so well insulated but it can be seen and measured with the right scan tool. Now, multiply that hundreds of times for one trip, thousands of times a week for a hundred thousand miles and the piston rings usually give up first, followed by a cracked piston or two. Plenty of men have documented this on YouTube such as IDoCars and CrazedPerformanceRepair.
I reckon that if the engine is babied and or runs in a cooler climate and or a higher altitude this knocking and pinging will be less.
It doesn't make sense to me to spend hard earned money on a premium vehicle and then cheap out on operating costs. Decades of driving has taught me that good maintenance makes for a very reliable vehicle.
From my 2013 GMC Sierra Owner's Manual:
As for me and my house, our engines are indeed fed a steady diet of Top Tier fuels or run on E85. Chevron and Sunoco are our preferred stations but I have run quite a bit of Shell 93 as of late in an attempt to prove one of my previous assertions wrong, maybe.
I believe those who run low octane fuels for well over 100K miles without consequence are the exceptions to the rule. Again, this belief does not apply to direct injected engines. Thanks Gary!
@Miami-Dade
