1986 420SEL - low oil pressure
 

I have done countless searches on this subject to no avail. Would someone knowledgable about this subject please help me understand the possible causes of a gauge that doesn't change much from idle to full gas; about 1 on the 0-3 scale.

Is this a faulty oil pump, or possibly more than that?

Thanks.

Simon Shearer

oil pressure
 

You might just need a new oil sending unit.

Maybe somebody put synthetic oil in the engine. The oil pressure sensor can't 'read' that right. I'd change the oil to mineral (as it should be) and see if the oil pressure gauge doesn't start working again, all of a sudden like......best of luck

I put synthetic in my 300E and it did not change the oil gauge.

I was assuming the oil pump needs to be replaced, no?

Don't assume the worst until you've eliminated all else. Disconnect the wire on the sender, test the gauge. If that's OK, then you change the sender (cheap compared to what an oil pump would be). I don't remember if its voltage or ground you use to test the gauge, but that's why service manuals and forums exist.

I have not experienced any strange behavior due to syn. oil. They're close enough that I don't think a mechanical sensor would care.

Would that be an "oil level sending unit;" or an "oil pressure sensor?"

at any rate, that's what I would do...change the oil and filter to good old Castrol GTX 10w-40 and Fram and see if that oil pressure gauge doesn't come back up. Heck, you should do those two things anyway along the way....

Since we are talking about the oil pressure gauge, it follows that the oil pressure sending unit would be involved. But oil level could indeed be a cause for concern. Back to the basics......have you checked the oil level, with the dipstick, as per the owner's manual (engine not running)? How long since the last oil/filter change?

Today. Changed oil and filter. Castrol GTX 10w-40 as recommended. No change on the gauge. In fact it hardly moves off zero now.

Next step a new oil pressure sending unit.

Simon

that was it...!
 

I changed the oil pressure sending unit and now I have the gauge leaping to "3" immediately when given gas. :D

At idle it settles down to about "2" - is that right?

My 300D idles at about "1."

Thanks for everyone's help - especially for stopping me rushing off to purchase an oil pump!

Simon

On my 500SEC, idle runs around 1.5, 3 at cruise rpms.