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!

[JimSmith]

Something very similar happened to my son's 1985 190E 2.3-16, only he drove it for a while. Turned out the metal filings that were created by the chain eating through those pins the guide mounts on, and between that the clogged oil pump suction screen the low oil pressure caused connecting rod bearing wear. In a 16 valve 190, a worn connecting rod bearing at piston number one will preclude reaching the desired "normal" oil pressure.

So, while you have the engine out, change the connecting rod bearings. Go to number one and do the plastic gage bit to measure the as installed clearances. If number one is bad, there is a good chance the rest of the connecting rod bearings suffered from low oil circulation as well. On the 16 valve engine these were pretty easy to replace. We changed the bolts as well rather than try to measure them. All in all, without taking the engine out, we did this part of the job in a few hours over a couple of days. Laying on our backs under the car. With the engine out I can't imagine how much easier it would have been.

You should try to find out which of the other sprockets the chain comes into contact with caused the problem to begin with - in our case it turned out to be a slipped bearing that closed the oil supply passage on the sprocket that I believe runs the distributor and a fuel pump on other 190's. One that bearing failed the chain began to wobble a bit and that extra motion took out the chain guide. My point is, the chain guide section probably didn't just erupt. Something else has caused the chain to cause the chain guide to disintegrate.

Good luck,

Jim

[Texholdem]

Originally Posted by lorainfurniture

Specifically the M103 engine.
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!

Looks like a $500+ restauration to me l

[lorainfurniture]

Jim,

The timing chain guide broke when the head gasket was done about 30k ago
I know this to be a fact. (because I broke it and was to ignorant at the time to realize the potential affects.)


tex, 799. and some change.. The motor mounts where 80 bucks each, and the tranny lines werent much cheaper.

The guts were actually pretty cheap.

[BenzMacX]

Hey, I am JimSmith's son.

My timing chain ate my guide rail quite some time before the catastrophic chain failure (it ended up eating through the tensioning rail and started on my aluminum head, but was stopped by the steel chain tensioner).

When it ate the guide rail, I spent the winter trying to figure it out (low oil pressure) before giving up and sending it to a merc mech. He drained the oil and pulled my digested guide rail out. It had been getting sucked into the intake of the oil pump and clogging it all up. Anyway, it was probably caused by a bad timing chain tensioner (it was the old style with just the spring) so make sure you replace that. If it were me, I would probably go and replace just about every bearing I could in the front cover. No point not to, you are already there. I would also do the crank-conrod bearings, also replacing the bolts that hold them in. Not very hard to do once you have the oil pan off (which you will need to take off anyway)

The epic failure that happened later could have been cause by a few things, damage from too low oil pressure, fuel wash or OVER pressure. The oil pressure relief valve on a 16v is a stainless piston in an aluminum hole so it will gall and eventually get stuck. Not sure how it works on the 300s, but if the relief valve is in the front cover (as it is on a 16v) I would lap that and replace the piston and spring. Again, no point not to.

Jim

[engatwork]

When it warms up a little I'm going to pull the engine out of my '95 E300 to see what I can find. I'm thinking I probably need a new oil pump. After running hard on the interstate it will drop down to around .5 bar when I stop and let it idle. It is showing 254k miles. I think the oil was not changed the way it should have been changed before I started maintaining it for the original owner about 7 years ago. I'll probably just go on and go through the engine when I tear it down.

lorainfurniture how many miles are on the one you are in. I went into a '92 five cyl turbo diesel one time and found the oil chain tensioner was the one that was worn the most.

[lorainfurniture]

Im only at 190k.

I bet you have a similar issue.. When you cold start, does the pressure peg higher, then go down?

[engatwork]

On cold start oil pressure pegs out and stays there till it is up to temperature. It does what it does after getting up to operating temperature. I believe I can see slight improvement right after an oil change.

[lorainfurniture]

Originally Posted by engatwork

On cold start oil pressure pegs out and stays there till it is up to temperature. It does what it does after getting up to operating temperature. I believe I can see slight improvement right after an oil change.

That was my EXACT symptoms..

Best way to check is take the upper timing chain cover off. (It probably leaks anyway )

[lorainfurniture]

Does anybody know torque specs for the flywheel bolts?

[lorainfurniture]

Part 2:
This is what your guides should look like.


Regretfully, I did not take as many pictures as I would have liked, but you can see the overall progress.


Finish installing pulleys, power steering pump.



I always opt to instal the intake manifold after the engine is in. It just seems to me that everything is easier to get to .

Once you have the engine/trans settled in, secure motor mounts, trans mounts, and start plugging everything back in!


Before your sart your engine:

1. Check your oil level
2. Look throughout the engine bay for loose, disconnected wiring
3. Check again
4. Look a third time to make sure you did not leave tools in there
5. Check the rest of the fluids
6. Re connect the battery
When you first crank, the engine wont start until after about a minute of cranking. This is because fuel is still making its way to the injectors.

If it doesn’t start after a minute or so, double check your connections. My car wouldn’t start because one of the fuel lines dripped out all of my fuel.

Once you get the engine started take another look to make sure you have no profuse leaks.

Top off fluids as needed.

Enjoy the fact that you wont be needing any more engine work for another 150k.

When you do work on your engine again, you wont have to deal with 20+ years of grease and dirt!


If anybody wants to chime in on anything I might have omitted, please, feel free.

[latief]

awesome pics...

The only thing i would have done different was to change the oil pan gasket (if you have not done that) and replace the fan bearing bracket....mine died a week after i finished my head-gasket ....it was not fun to go in and replace that after all the work...

good luck!

[compress ignite]

M103

Auto-Tranny: 30Nm + 90 Degrees.

http://www.ps2cho.net/downloads/MB%20CD/W124/w124CD1/Program/Engine/103/03-4100.pdf

[S-Class Guru]

Interesting thread.
I've been slightly concerned with a little whir sound from the oil pump/lower chain area for the last few years. But it doesn't seem to get worse, so I've resisted going in there.
Re: oil pressure. Mine pegs the needle when cold, or over 1200 RPM when hot.
However, when really hot and then idled down to 600 in Drive, it will drop to
0.7 BAR or even a bit less. It's done this for 15 years. I use 10-40 oil.

The plug-on connector on my prssure sending unit has loosened a bit over the years, and can cause the gauge to move around randomly sometimes

DG

[compress ignite]

The FSM says O.P. "May" drop to .3 Bar (HOT @ Idle) [Allegedly with no Worries]

The Question always is: .3 Bar on a REAL Mechanical/Bourdon Tube Type Gauge
OR
.3 Bar on the "Representation" of an Oil Gauge Mercedes supplies in the I.C. ?

.3 Bar by my computations is roughly 30% of (14.5038 P.S.I.) or 4.35114 P.S.I.
'Better than ZERO,Except my non magical boxers are WET, if I see that figure on the Gauge!