Elmo, Thanks for your thoughtful remarks regarding my use of mid-grade gas in a Lexus 300G.
Actually, we did read the manual cover to cover several times, but being an engineer, I wondered if the computer engine control would automatically adjust the timing, etc, to compensate for lower octane without harming the engine. One Lexus mechanic, on the condition that he wouldn't ever admit saying so, assured me that the computer would compensate the lower octane, but that the mileage might be lower.
I carefully checked the mileage for the first six months using the highest grade gas, and then for the next five and a half years using mid-grade. There was no significant difference. The car now has almost 80,000 miles on it, and is purring as good as the day it was new. The only mechanical problem to date was a leaking water pump - replaced by the Lexus dealer at no cost.
Not bad for a brain-dead owner, don't you think? BTW, not having a lot of money has never been one of my problems. I actually bought the Lexus because it is a more cost-effective car to own than many cheaper automobiles. And a lot more pleasurable to drive.