240D High oil pressure
 

I just bought a 1977 240D with bad auto trans. I watched it set at a garage all summer, and finally stopped to see if it was for sale. Before I tear the trans out, I wanted to check the engine. It started up with no trouble, and sounds good, but the oil pressure pegs out at all times, even after warmed up. (peg is at 45 psi). I drained oil and put in some lighter weight (its cold here in Nebraska!), but that did not help. I hooked up a different oil pressure gauge, and it shows 70 psi at idle, and maxs out over 90 psi when I rev up. I took the sump pan off, and it was nice and clean, no loose metal. Also cut open the filter, no metal there.

I have a '76 240D that was ran out of oil, and it did same thing. It is on the engine stand now being torn down. Lots of metal in bottom of that pan.

I read some posts regarding 240D oil pressure, and it seems they might 'peg' the oil gauge a lot. This new 240D has 118k miles (at least), should I tear down and inspect, or look for faulty pressure regulator on oil pump? Or is there something else I am missing?

Thanks for any help!

That's the way it should be. The oil pressure gauge should peg when cruising. It's only at idle that it might drop to 15psi/1 bar and it usually has to be pretty darn hot out and/or after running it hard for that to happen.

The gauge is either marked as 0-15-30-45 psi or 0-1-2-3 bar which are roughly the same scale.

Sixto
95 S420
87 300SDL

Those motors can have just assume oil pressure. At one point the pressure relief valve was in the oil pump and at another it was in the block. We happened to rebuild a motor once and replaced the oil pump and we got the wrong one. We had no oil pressure relief valve. After a period the gauge in the dash broke and leaked oil. Strange we thought and then it did it again.

We looked at the pressure and cold it would hit 180psi. Eventually we figured it out.

BTW the real early cars had full range gauges and the story I heard was that MB cut the gauge max to basically make it an idiot light. They didn't want people worrying about why on a hot day the pressure would be less than a cold day. They just didn't want concern over quantity of pressure. They wanted a qualitative measure.