Join Date: Jul 2015
Vehicle: 2001 SLK320
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I researched this as best I could when I had the 1998 pre-facelift SLK230 Kompressor like yours, and concluded that normal Unleaded 91 was fine.
Whereas my SLK320 uses minimum 95.
Overseas reviews and sources are confusing as what we call normal Unleaded is sometimes called Premium as they have/had a version that was 87. Some countries use 95 so commonly that it is the normal grade. And different countries use different terminologies, RON, Octane and others that have different definitions and lead to different “ numbers”.
I’ve stated this in a vague way as I don’t want to get into an argument about whether or not I misrepresented what some other country does.......
I was surprise that a supercharged engined ‘230 was ok on 91 ! But careful reading of the fuel label terminology ( a bit ambiguous if I remember, ) the Australian version of the owners manual and suppliments, and also contemporary Australian Road Tests, I confirmed to myself. It ran fine.
You should not take my word for it, but check my logic.
Higher rated fuel may not make a difference with respect to fuel economy or power.
Although the car has a oxygen sensor, unless the engine control module is designed to reset engine parameters to match the fuel grade, it won’t do much good.
I recall the Astra from early 2000 was designed to run on 91, but gives about 3% more power and similar economy improvement on 95, but for an increase of about 12-15% fuel cost increase at that time.
And extra power is really only of use if one is using all of what is already provided, and who can notice an extra 3% anyway?
Fuel economy of the SLK230 is better than the V6 and the 91 fuel is often now 15-20% cheaper. A nice bonus for the ‘230 if it gets lots of use.
Around me several retailers have dropped 95 and only sell 98, raising the cost even more. So many cars need 95, what are they to do?... They’ll pay more and buy the 98. Very cynical strategy from the retailers.
So a long answer to the question.
I now recall it is spelt out on only one page of the manuals and it’s not where I expected.