Oil Pressure Story - PeachParts Mercedes-Benz Forum

pondmann · #1 09-03-2004, 10:22 PM

I have had my 1981 300SD for 2 weeks now and absolutely loke it. 98K miles and so far I have changed the following small things:
1. Primer pump.
2. Fuel hoses under tank.
3. Steering pump fluid.
4. Power windows white thingy to move it up and down.

Going home today, noticed oil pressure was not going above 2 bar. Idled there and flinched just a little when I stepped on it a little. Temp OK. stopped car looked under hood and under car, OK. Saw oil sprayed on cam then decided to take back roads and keep RPM close to idle. Got home, disconnected battery came to this forum, read for about 1 hour. Went back out, conneted battery, started car and now idled below 1 bar. Turned it off, looked under the hood, cleaned and replaced contacts on everything in the fusebox while I was trying to figure out where to start. Saw a loose vacuum to that black thingy on top of the valve cover (connected to throttle linkage - what is that thing - vacuum connection looked loose) and fixed it. Started the car and everything was OK. I have driven it around town for 10 miles since then and it still OK.

What was that all about? Is it a fuel pump failure warning, (100K miles now) or just an electric glitch. Previous owner changed oil at dealer the day I bought the car and I have the paperwork - I am changing oil again tomorrow and sticking with RotellaT like PO.

SD Blue · #2 09-04-2004, 10:52 AM

If I understand your description correctly, the black "thingy" on top of the valve cover is for control of the EGR valve. It should have nothing to do with your oil pressure reading.

A couple of things to check for the problems you described. The oil pressure sending unit is on the side of the oil filter housing. Check the electrical connection. Also, check the main grounding strap from the chassis to the engine, including the bracket it attaches to. It is located on the passenger side near the starter. Finally, check your battery ground cable at both ends to ensure there is no corrosion.

pondmann · #3 09-04-2004, 02:35 PM

Thanks for the suggestions, I will check them out today.

Update: Started the car this afternoon and oil pressure jumped all the way to max at idle? This in my opinion is a better problem than oil pressure not rising but it's still a problem. I will check electrical before going to mechanical. Tomorrow I might drop oil pan to see if there's anything fishy down there. Anyone know where I can get an oil pan gasket off the shelf? NAPA etc any good? Dealer is closed now.

R Leo · #4 09-04-2004, 04:07 PM

Aren't the oil pressure gauges on SDs mechanical? If so, then nothing with the electrical or vacuum systems is going to change that reading. Do an oil change ASAP and make sure you pull that oil filter and stab a new one in. Sounds like it's got either the wrong oil or filter in there.

Palangi · #5 09-04-2004, 04:14 PM

I think the SD oil pressure gauge is electric.

I agree with Randy. Put in a new oil filter, and make absolutely sure you have the right one. When you take the old filter out, look in the filter cavity and make sure there are no grommets from previous filters in there.

#6 09-04-2004, 04:48 PM

When my 300SD is cold (the gauge is electric on mine atleast) the gauge rockets up to the max at idle until it gets up to temp where it hovers between 1 and 2 (1 being no pressure...it never drops to zero)
I think the gauge is there to say "the oil pressure is fine, the oil pressure is on the low end, the oil pressure is zero"
just remember...atleast on mine...the 1 mark is zero....turn the car on before you start it see where the minimum is...it may freak you out at idle once it is warm but I wouldn't take notice unless you were doing 1500+ RPM