OM603: Low oil pressure sometimes, showing 0. - PeachParts Mercedes-Benz Forum

ah-kay · #1 03-17-2021, 05:03 PM

I have a problem with an OM603 wagon. The oil pressure pegs at 3 at startup, then it can suddenly drop to 0 on driving. Then it may creep up again to 2 or 3. I do see oil dancing out of the valve cover if I remove the oil cap. However, I don't have a chance to do it when it was showing 0 on the gauge. I suspect the low oil pressure may be real as my newly installed turbo seems to be damaged. I changed out the oil pressure sender in the oil filter housing but the problem remains. My next step is to change out the oil pressure gauge on the dash. What could be wrong?

1) Oil pump in the sump is slipping?
2) Blockage in oil passage?

Any insights are welcome.

jojee · #2 03-17-2021, 05:39 PM

There are 2 small o rings on the stem/rod that goes through the oil filter. Check those and if need be replace them. That should help. Yes f that doesn’t work check the oil pressure sending unit. This is where I would start.

Frank Reiner · #3 03-17-2021, 06:11 PM

Quote:

Originally Posted by ah-kay

I have a problem with an OM603 wagon. The oil pressure pegs at 3 at startup, then it can suddenly drop to 0 on driving. Then it may creep up again to 2 or 3. I do see oil dancing out of the valve cover if I remove the oil cap. However, I don't have a chance to do it when it was showing 0 on the gauge. I suspect the low oil pressure may be real as my newly installed turbo seems to be damaged. I changed out the oil pressure sender in the oil filter housing but the problem remains. My next step is to change out the oil pressure gauge on the dash. What could be wrong?

1) Oil pump in the sump is slipping?
2) Blockage in oil passage?

Any insights are welcome.

a-k:

Is there any consistent relationship between the drop in pressure and driving time, or time and engine temperature? If so, there may be a blockage in the oil cooler or the lines between engine and cooler.

Diseasel300 · #4 03-17-2021, 06:50 PM

I'd be more suspicious of the oil pressure sender failing. Every 603 I've had has done this and a new sender always rectifies the situation. Every one of them behaved exactly like this one. 3bar at cold start, then random dropouts or periods of "0" oil pressure once warmed up.

engatwork · #5 03-17-2021, 07:13 PM

You would probably hear some unusual top end noise if it was actually going to 0.

ah-kay · #6 03-17-2021, 07:23 PM

Quote:

Originally Posted by Frank Reiner

a-k:

Is there any consistent relationship between the drop in pressure and driving time, or time and engine temperature? If so, there may be a blockage in the oil cooler or the lines between engine and cooler.

I will check this. Thanks.

ah-kay · #7 03-17-2021, 07:25 PM

Quote:

Originally Posted by Diseasel300

I'd be more suspicious of the oil pressure sender failing. Every 603 I've had has done this and a new sender always rectifies the situation. Every one of them behaved exactly like this one. 3bar at cold start, then random dropouts or periods of "0" oil pressure once warmed up.

The sender had been replaced. It is in my post. The problem remains.

Diseasel300 · #8 03-17-2021, 08:12 PM

Quote:

Originally Posted by ah-kay

The sender had been replaced. It is in my post. The problem remains.

I saw, and my point remains valid. New doesn't mean good. Is the replacement actually a brand new VDO, or is it some off brand? I had an FAE branded one bad out of the box.

ah-kay · #9 03-17-2021, 08:27 PM

Quote:

Originally Posted by Diseasel300

I saw, and my point remains valid. New doesn't mean good. Is the replacement actually a brand new VDO, or is it some off brand? I had an FAE branded one bad out of the box.

How long is a piece of string? I believe the old and new one are good. I have eliminate faulty sender possibility. I am looking at the gauge. I put 'another' one in today.

Alec300SD · #10 03-17-2021, 11:08 PM

Could be just a poor electrical connection at the sender.
Engine vibrations can cause the connection to randomly fail.

Temporarily add an alligator clip type test lead between the sender and the sender wire to see if the problem disappears.

filp · #11 03-17-2021, 11:14 PM

Liquimoly engine flush then new oil? That should remove any sludge

ah-kay · #12 03-18-2021, 06:19 PM

I put in a "new" pressure gauge and the problem is the same. What I have observed today is that the problem happens when the car is going uphill so I suspect oil may low. It was low by a quart but it should be fine. I top it up and the problem is still there. Also I remove the oil lid when the pressure is low and I don't see oil dancing around as much so the problem may be real. The line to the oil cooler is quite large, a blockage on the line is unlikely. Could it be a blockage inside the cooler? I am going to remove the sump side door and take a peek at the oil pump to see anything unusual in there. It is a royal pain to remove the oil pump to inspect it.

t walgamuth · #13 03-18-2021, 06:42 PM

I was wondering if the oil might be low. Also could be a problem with the pickup in the pan.

ah-kay · #14 03-24-2021, 02:22 AM

I looked at the oil cooler lines today. The oil cooler is fed by 2 lines from the oil filter assembly, one in the middle of the filter body, one at the bottom. Anyone knows which line feeds the oil to the oil cooler? Which line returns to the oil filter? Thanks.

Alec300SD · #15 03-24-2021, 03:02 AM

Lower nipple on oil filter housing = outlet, uncleaned oil flows out towards oil cooler.
Upper nipple on oil filter housing = inlet, uncleaned oil flows in from oil cooler.