I bought my 1996 Bonneville SSEi brand new. I didn't have much time in those days, so I just followed the manufacturers recommendation and only filled it premium (high octane) gasoline. I didn't want to run the risk of knock damage. Now that the internet exists, and I've stumbled across this forum, I thought I would ask: have I been flushing my money down the drain all this time by buying premium gasoline? Could I have gotten by with medium octane, or even regular octane? :?: Since I'm not selling soon, I can maybe still save a few bucks. Heck, a real answer to this could save us *all* a ton of dough.

Not sure, but my '92 even knocks a bit with premium. You would most likely lose performance because the computer would retard the timing when it senses detonation.

Yep, you were using correct octane and not wasting money at all! Unlike your dashboard in the 96 mine has Premium Unleaded Fuel Only on there to le me know not to use anything less. I sometimes am glad to have that as a reminder for my car because it has been times by mistake I will oick up the 89 and have to look up again and get the 93 pump. I think this mistake can have you spend unnecessary money

Your SSEi NEEDS premium gas. Without premium gas, you will get detonation, so the computer will detect the knock, and give you knock retard, which retards your timing advance so you loose power, not to mention the fact that detonation can badly hurt your engine. If you have to run 87 or 89 octane in your car, I seriously suggest putting something under your gas pedal so you can't press it more than ~70% of the way. But, unless you have done mods to your car to reduce detonation a significant amount (i.e. Intercooler, headers and full exhaust, high lift cam) you should definately use Premium. Your car will thank you later.

I tried the cheep stuff once and literally needed to fill back up the next day. You'll get about the gas millage of a Hummer.