[JimD]

Tock,

Thanks for posting the Shell comment that their premium has more cleaning agents than their regular. When I looked at their website I did not notice that. If I had, I would have worded my previous comment differently. So more cleaning agents are an advantage of premium.

My guess is that would be more significant for the dual turbo motor BMW makes (forgetting the codes at the moment) that tends to build up carbon in the intake. I'm not sure how significant it is for my normally aspirated motor.

My personal theory, based mainly on a post on the "Bob is the oil guy" site, is that using gas from different suppliers at least occasionally is important to reducing deposits. This thread was from a guy that claimed he used a brand exclusively for 10k miles or something, tore the engine down, looked at it, then put it back together and tried a different brand. He found different deposits for different brands but not grossly different amounts of deposits. He believed that one brand tended to remove the deposits of other brands so now he rotates. I use Shell mostly but justify the occasional "off brand" fillup as potentially removing deposits from Shell gasoline. This is just an untested theory that makes some sense to me, may not to others.

The main point of my original post was to supply some data from my vehicle suggesting that others see what the difference is for them. I still disagree with the premise I got from your article which I read as saying we all should use premium. I don't think the unquantified greater amount of cleaning agent justifies the significant premium in cost to me. But I respect other's right to spend their money as they choose. I also suggest that before you or anyone else assume it will help your gas mileage you try it and see. You might be surprised. I expected my mileage to be a bit better with mid-grade (89 octane) and it was not.