Diagnosing low oil pressure symptoms for your mercedes

[lorainfurniture]

Specifically the M103 engine.

A few months ago, my 89 300e started to develop a problem regarding low oil pressure. I decieded to do this little write up so that others can benefit.

Symtoms: Upon start up, car would immediately go to 2.5-3 bar. (normal). After about 5 minutes of idle, pressure would drop to about 0-.75 bar. (not normal.) At wide open throttle, (well, 5k rpm) I would be at 1.5 bar.

First things first. Check your oil level!!!! After you verify proper oil level, the next logical step would be to check your oil pressure sending unit (oil pressure valve.) This is located right on your oil filter housing. See pic below.



I assumed that this was the problem, so I immediately ordered it from Phil.

It was not….

So that brings us to rule number 1: Don’t make assumptions! This part was relativly cheap in respects to others, but still cost me $70. The TRUE problem part was less than $10 to buy. Continue reading to find out..

Instead of throwing more parts at the car, I decdieded to invest in a mechanical oil pressure gauge from harbor freight:

$20 well spent.

At this point I can tell whether the low oil pressure reading is an electrical failure, or a mechanical failure.

Simply unscrew the oil pressure valve, attach the required fittings, and start the car to see what happens.

In my case, the readings were identical. So that tells me that my problem is somewhere in the engine……

So, now to the fun part:

My theory is that something is causing blockage in the oil pump, or the oil pump itself is going bad. There are many different ways to address this problem, like unbolting motor mounts and raising the engine enough to remove the oil pan, but, never pulled my M103 motor before, and was itching to do so!


Im not going to bore you with the whole engine removal process, nor did I bother to take any pictures. Ill start off with the engine out, and ill post as the engine gets back together.

With the engine out, and on a stand, This is what I found:





That’s it! The first picture shows the timing chain, and its missing the entire guide!
(that would be on the right side of the chain. )

Since I have the engine completely out, now would be a good time to change a few “while im there” parts.

1. oil filter housing gasket
2. bypass valve
3. oil pump chain
4. water pump
5. timing chain
6. timing cahin tensioner
7. timing chain guide
8. front main seal
9. rear main seal
10. motor mounts
11. trans mount
12. new transmission cooler lines.

I orded a variety of other things, including a couple of stripped bolts, pins etc..

Now im waiting for all of my parts to arrive from phil, I will post again with pictures with the rebuild/re install of the engine.

Keep in mind, this is basically my first time doing a job like this, feel free to chime in with any input/ advice

Thanks!