No, not a joke here, but a question... In part from suggestions from other members of the forum, in part because of a suggestion from a dealership service manager, I started using mid-grade 89 fuel in my car about a year ago, a change from the top grade 91 or 93 I had been using. I couldn't detect any driveability issues, fuel economy remained the same, power seemed unchanged, but oddly enough the engine seemed to run more smoothly on the 89 vs. the 91 gas
. Okay, fine with me, and at about a 10-cent per gallon price differential, I was saving a little money.
Lately, however, I think I'm detecting some knocking when the engine is under load, such as accelerating or climbing an incline. I can only hear the knocking when the sound has something to bounce off, such as tunnel walls or a nearby vehicle. Obviously I'll be reverting to the 91/93 grade for the next coupla tankfuls to see if that eliminates the apparent knocking, but nonetheless I have a few questions:
1) Is 89 mid-grade the wrong stuff to use on a regular basis?
2) How well does the knock sensor compensate for lower grade gas?
3) Does the onset of summer weather, and the seasonal formulation of gasoline, have an effect here?
4) With high mileage on an otherwise well maintained engine (200,000+ miles) is carbon buildup inevitable, calling for higher octane fuel?
5) Might I be hearing something other than knocking (like the marbles in my head for instance)