My father has just purchased a 1998 C230, the year before it was supercharged. He asked me if it would be okay to run regular (87 octane) in it as opposed to premium (91 octane). It says on the gas door to use premium, but I was curious if it would harm anything if regular was used? In my 1988 300E, I have read on this site that it is fine to use regular. I understand that in some cases it is recommended to work better with old injectors etc. I also have a friend with a 1994 C220 that has only used regular for the past 5 years with no problems.

What are your opinions on this?

TIA,
Steve

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1997 E320
1990 Nissan 300ZX Twin Turbo (Stage X+)