Fluctuating oil pressure gauge 87 300D

[lietuviai]

Lately for last few weeks, the oil pressure gauge in my 87 300D has been fluctuating. It has even dropped to 0 or barely goes above 1 bar. Most of the time it stays at 3 bar while driving but it's the times it drops to 0 that has me nervous. It'll stay on 0 for long periods of time then jump back to normal. I haven't had any abnormal noises nor any high temps during the oil pressure drops. I've checked the wiring as best I could and even changed the sender with no improvement. I've even changed the 2 orings on the oil filter lid tube thinking it might help but it didn't. I'm puzzled and don't know where to go next. I've driven it like this already for over 2000 miles so I'm thinking it's not serious because nothing bad has happened. I'm just tired of looking down at the oil pressure gauge all the time.
Need help.
Thanks.

[Ali Al-Chalabi]

I would start by hooking up a mechanical oil pressure gauge to the test port and verifying the accuracy of the gauge in the dash.

[lietuviai]

I was thinking about doing that but I need to find a metric fitting to match the mechanical guage I have. It's also a PITA to get to the area the sender is in. I was wondering if there was something else I needed to check before doing all this.

[Ali Al-Chalabi]

If the engine is actually operating with no oil pressure especially if the oil pressure is low when above idle rpm, it will damage the engine. Judging by the fact that the oil pressure indication randomnly drops and goes back up may lead me to believe that it may be the gauge that is the fault.

[speedy300Dturbo]

The factory service manual mentions something similar to your problem, and indeed the remedy is to replace the gauge itself.

[lietuviai]

Originally Posted by speedy300Dturbo

The factory service manual mentions something similar to your problem, and indeed the remedy is to replace the gauge itself.

Do you recall where in the manual it writes about it? I was actually planning on retrofitting a manual gauge from say a 123.
The less electronics the better.

[Hatterasguy]

Its a 603 if you lost oil pressure you would hear it! Your lifters would go freaken nuts!

Sounds like a ground problem? Clean connections, if that doesn't work replace sending unit.

[lietuviai]

That's what I would have expected if it were really a oil pressure loss. I've tried going through all the visible wiring and I did replace the sender but no improvement. I wouldn't doubt if there is a bad ground somewhere that I'm overlooking. I've had that happen with my tail lights.

[t walgamuth]

i would check grounds.

tom w

[Hatterasguy]

I wish I could offer you more help. I checked my CD and I didn't come across anything that would help you.

Good luck!

[CSchmidt]

My old SDL did that sometimes as well. I replaced the sending unit but it would still happen now and then. The major contributor to when it would happen was long drives (like 300 miles) or really hot weather.

I know nothing of the inner workings of the MB oil pump, but I was wondering if there was a spring that was getting worn or fatigued in the bypass part of the oil pump - and therefore weaker after a heat soak?

The pressure would go back up after just a few minutes of cool down typically.

Good luck, it never seemed to harm the car. I never noticed the lifters get louder either.

Chuck

[lietuviai]

I'm going to go through the grounds as best I can. It's nerve-racking to see the gauge at 0 or barely at 1 at times when it malfunctions. My fluctuations aren't temp dependent. Its been up and down regardless of temp.

[lietuviai]

I found out that the gauge is the root of my problem. I've been driving it lately and when ever the gauge drops, I smack the gauge cluster and it pops back up to normal. So it seems that the gauge is to blame. What a relief!