m103 low oil pressure. need advice before I do something drastic! - PeachParts Mercedes-Benz Forum

lorainfurniture · #1 12-08-2009, 10:41 AM

I have been having this problem as of lately with my 89 300e. One day, the oil pressure gauge dropped from 3 bar to 1. at idle almost 0.

During normal driving, it will go to about 1.5-2 bar.

First thing I thought to do is replace the oil pressure sending unit.

No change.

It would be silly to actually start throwing more parts at the car, so I went to harbor freight, purchased a mechanical oil pressure gauge.

My reading on the mechanical gauge is consistent with my gauge on the dash.

So my conclusion would be that the engine truly has low oil pressure.

Heres the thing: If I take off my oil cap, I can physically SEE the oil squirting on to my camshaft via the oiler... at idle.

If I rev to 2k rpm, there is plenty of oil to be had at the top of the motor.

No strange noises, clicking, or tapping. AT ALL. Ive been driving the car like this for a couple of weeks, and the car still runs great.

Whats the next move? As you m103 owners know, the oil pan is a bit of a job to remove. I just wanted to hear some advice/ maybes before I open up a can of worms.

bsmuwk · #2 12-08-2009, 06:28 PM

what weight of oil are you running?

tinypanzer · #3 12-08-2009, 06:35 PM

Oil weight can matter all right.

A clogged oil filter along with a stuck bypass valve could make your pressure drop. The bypass valve is built into the motor on M103, where most cars depend on the bypass valve being in the filter can.

lorainfurniture · #4 12-09-2009, 02:46 PM

When the pressure drop happened, I was using rottella 10 40? Not 100%. sure.

I switched to mobil synthetic, and it helped a little as far as raising oil pressure. (still not good, but just above 0 now.)

On a cold start, oil pressure will jump to 2-2.5 bar, once the engine warms up, back down to 0

thanks for the replies, I hope I can resolve this problem before it starts snowing!

MDE3 · #5 12-09-2009, 03:11 PM

Oil pump pressure relief valve...maybe got some dirt/plastic from chain guides into the valve causing it to stick. Not sure where it is on the 103 motors..but familiar with the ones on the 2.3-16V.

Bad crank bearings (spun) is one of the most common problems with dropping oil pressure. However usually when this happens it will give you an indication...pressure will fluctuate..when you have pressure..The needle will flicker regularily as the bearing spins on the crank. This pressure flickering is what let's you know it's the crank.

lorainfurniture · #6 12-09-2009, 03:41 PM

Does anybody know if the oil pressure relief valve is accessed from the oil pan?

Im thinking you are right about the chain guides.

Im thinking, if I pull the motor, I could do the oil relief valve and guides at once, problem solved..