OK so this may sound paranoid, but it just seems like my car always has great oil pressure.. when I turn the key to the on position (before cranking), the oil pressure gauge pegs to the top to the 3 and pretty much stays there (even after the engine is started and running). Im starting to think the oil pressure sending unit might be bad.... Any ideas?

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With the engine off, there is no oil pressure. Your sending unit is either simply defective, or has a wire grounding out somewhere.

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~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL

Something is wrong, I don't think you should be seeing any pressure before cranking the engine over. I think at idle I see around 1 Bar and it will increase to three with higher RPM's.

is it hard to replace the oil pressure sender? Or troubleshoot this problem?

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Mine did the same thing, there was a plug loose behind the insterument cluster. Just pull the cluster and make sure everything is pluged in.

As I understand it, the SD has an electric oil pressure gauge with a sender one the oil filter housing somewhere. As others have said, you are most likely looking at a bad sender or a disconnected wire at the sender. Less likely but not impossible, a bad connection at the gauge.

Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

replacing the sender is pretty easy. A 17mm open end wrench is the only tool you need.

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1981 300SD 512k OM603