The octane rating of the fuel should be as recommended by the manufacturer.
If you don't have the manual then ask Merc.
BTW, what you mean by "premium"? What matters is the octane number, not an
adjective (whose meaning can vary across the world).
For direct contact replace nospam with schmetterling
Premium fuel in the US usually means 91 octane as that is as high as I have
ever seen at any of the big name gas stations. MB has said for many years
in the owners manual that you should use "premium" fuel. I hav been using
regular in my 1986 560SEL for 10 years with no problems. Engine runs great,
no pinging. The ignition system automatically retards the timing when it
senses that the fuel may cause pinging. If you are interested in maximum
acceleration and high speed driving you should use premium. If you just
drive the car normally then regular works just fine.
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