Octane Question

I have an '86 560 SEL with 106K miles. I have owned the car for 6 years and have always used regular gas in it. I know MB says to use premium and I sometimes fill with that, but 95% of the time I use regular. The gas octane in my area is 87 regular, 89 for middle grade, and 91 for the premium blend. I would think that after 6 years if anything bad was going to happen it would have already. So why is it that MB says to use premium? The car gets in the 17-18 mpg on the highway and I never get any spark knock in city or highway driving.

[G-Benz]

If you suffer no ill effects, then stay the course.

It's just a theory, but there may be additives in the higher grades that help with keeping injectors clean, reducing carbon build-up, etc., etc. Then again, it could just be "snake oil". Higher octane fules have a hotter "flash point", which inhibits detonation in high-compression engines, or lower-compression supercharged and turbocharged engines.

As your car gets older, some problems that might crop up could be solved simply by upgrading the octane you currently use.

The reason you get by with regular is that part of the ignition control system on you car is a knock sensor. If knock is sensed, the ignition is retarded to prevent it. Retarding the ignition timing, decreases power and increases fuel consumption. This is the subsystem that has saved your engine.

Good luck,