My oil filler cap (on valve cover) won’t budge when I try to remove it. I don’t want to blindly force it with slip-joint pliers, unless I know it won’t damage anything. Is there maybe a push and turn, adult-proof trick? Please advise.
Thank you.

no tricks. i've a few of these i work on that require channel locks to loosen. good luck, chuck.

The oil cap on my 300SE can be very hard to remove, occasionally I have to use a tool to loosen it.

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1979 Black on Black, 300CD (sold), 1990 Black 300SE, Silver 1989 Volvo 780, 1988 300CE (vanished by the hands of a girlfriend), 1992 300CE (Rescue).

Thanks...I’lll use my channel-locks on it. I just didn’t want to break anything.

exsailor66, recommend placing a rag over the filler cap instead of having the slip-joint pliers contact the filler cap directly, or wrap duct tape around the slip-joint plier jaws; otherwise you are going to gouge the surface. I position a 3/4" square dowel about 30" long on the right side of the filler cap flat and give it a rap with the heel of my hand to loosen it.

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Fred Hoelzle

Dunno if it's compatible with the old V8 but...

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#dontdealwithkahlil

The modern "high profile" caps used on the newer cars still fits the old cars. I think Mercedes has only ever used 1 oil fill cap design. I have the new one on both the SL and the SDL. The higher handle makes it a lot easier to get off and it doesn't leak.

VW/Audi caps are yet another option. Easy to grab and turn and seal well.

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#dontdealwithkahlil

When removing the cap with tools, apply steady even pressure and let the rubber seal slide along the filler neck. ( this also goes for stuck oil filters ) The seal will only move so fast and pushing very hard just leads to something breaking / slipping off.

Thanks all.

Try a strap wrench - it won't leave any tooth marks.