How bad is it to use 87 or 89 octane in a new Benz CLS550? I have a 2006 BMW 750 and Z4 and started using 89 octane when gas prices went up. I noticed no difference at all so I tried 87. I've been using 87 in both cars since the summer and no problems or noticeable difference in performance despite the fact that the cars "require" premium. Can I get away with that in a Benz or are they more fussy? Thanks.
It's not about being cheap. It's about wasting money on something you don't need.
I know it won't do any damage because the antiknock sensors will retard the timing if necessary. If there is no noticeable difference in power, then what difference does it make?
Interesting. Not to quibble, but there indeed is a distinct "cheapness" about this, particularly since you mention "when gas prices went up". This topic recurs whenever prices jump, but it actually costs more when it's cheaper. On average premium is about 20-25 cents more per gallon than regular, when gas was $4.50 a gallon it was less than a 5 percent premium. Now it's more than ten. So you're really paying LOTS more when the fuel is less expensive.
Second, I like that you "know" it won't do any damage. So why even bother posting?
The reality is that moving around a spark (dynamic timing), enriching mixtures and other compensating mechanisms can only do so much. When a car is designed for regular, it will often make changes that will often result in better performance. However, when an engine is DESIGNED for premium, there are certain aspects like compression ratio and static timing that no amount of electrical finagling can change. The manual states that regular fuel can be used when there is no alternative, but the owner should drive gently and return to premium as soon as possible.
While it is true that the electronic feedback systems will do all they can to prevent immediate harm to the engine, simply avoiding knock is not all there is. How about carbon buildup over time? Additional combustion by-products from incomplete ignition fouling the O2 sensors and killing the cats early? And if it's retarding timing and enriching mixture guess what? That's less power output per rev, which means you need more revs to maintain power or speed, and in turn, less fuel economy. Experiment all you want, but that's basic physics. (If you do wish to experiment, then keep good track of things, don't just depend on the dash readout.) And where does it end? If you could find 83 octane and save another quarter, would you?
The bottom line here is expense. I don't want to spend money I don't have to, but I also intend to keep my car for several years. Facing costly and needless repairs later to save a few bucks when I fill up strikes me as the dumbest way to spend money I don't need to. I chose to leave behind my Ford/GM mentality when I bought my MB, and if I want to apply that attitude to a benz, well, shame on me.
Take care and enjoy the ride,