M103 still burning oil...Need advice
 

1987 260E. Car has about 90k miles on it.

So 2 weeks ago I checked my oil level and it had not moved since I replaced my valve stem seals...Success for 2 weeks! I thought I had it solved...
Then today the oil light came on and there have been no drips under the car.

This engine's oil has seldom been changed at all throughout its life so I think the problems have caught up.

Compression is 190psi all cylinders, but I have 20-30% leak between each cylinder and there is a lot of escaping pressure I can hear through the timing chain area.

I am running Penzoil 20-50.

How can I know if its the rings? At this point the best idea may be to get a low miles 3.0L motor, (I'll rebuild the head) pull mine and start from scratch. I have a garage to do this.

Any thoughts or advice? The car visually is great and the transmission shifts amazing. Its just STILL burning oil.





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You say that the oil light came on, but was the Oil level actually low?

If not, than in could very well be a defective, or oversensitive oil level sensor. If it was indeed low, than obviously the problem is elsewhere.

I am just pointing this out, cause on my car I had an overly sensitive oil level sensor, and as soon as I was even 1mm below the full mark the oil level light would start flickering on.

Changing the sensor, made no difference. so I always had to keep it at the full mark. It never burned, or leaked any oil though.

It is definitely burning as I checked the level. I can smell it as well after I park the car right as I get off the freeway.

How did you gauge "success for 2 weeks"? Did you check the stick, or the light didn't come on?

I checked the stick and it hadn't moved. Or I wonder if bad valves could have already thrown the new seals out?

Maybe not bad valves, but that ring of crud on the valve stem could have damaged the new seals. I usually use a bit of Scotch Brite to clean up the valve stem when I replace the seals.

I cleaned it all up and lubricated accordingly. I did the same method as when I did my 300TE last year (which since has not burned a drop).

I don't think bad rings "come and go". But maybe a head gasket problem could. I don't know. But it seems odd you had no consumption for a while, then large consumption.

Is there a way to tell if the rings are bad w/o pulling the head?

Yes there is a way. It's called a LEAK DOWN TEST. Every garage should have this. I'm quoting from the "Technical Data Passengers Car" book from Mercedes Benz:

Total read out not higher than 25% leakage
on piston rings 20%
on valves and cylinder head gasket 5%

I assume you know how the test goes??

What kind of valve seals did you use?? I assume the original Mercedes packed in a Mercedes plastic bag with containing the "STAR" logo. Because there are so many suppilers out there and they don't have the right tightness from the spring inside the valve seals. On the next oil change use 40 wt. (oil) I had a similar problem. I'm not sure what kind of oil I used. Valvoline or Castrol and the oil consumption disappeared.

Well, if you can smell oil burning when you get off the freeway, then I think it's safe to assume that you have an external oil leak. It's possible for this to happen and not to see any evidence on the ground.

It could leaking while underway, when pressure is highest, and could be hitting hot engine parts like exhaust manifold/piping and burning off. Course it would take a while for you to see a noticeable drop, but it's a possibility. I would thoroughly inspect for leaks.

If it is your rings or something internal, then I would probably trying a different kind of oil, maybe some for "high mileage" cars? Maybe try some sort of additive at the same time. You've got nothing to lose at that point.

The valve covers have been known to warp.
Even a new valve cover gasket will not seal the cover to the head properly and a small leak usually at the rear adjacent the transmission dipstick/filler occurs.
Warps are generally caused by overzealous tightening of the hold down bolts - generally done at non MB specific service centres by persons not using a torque wrench.
It's easy to pinch the little half moon section at the rear of the valve cover gasket when installing it.

Leakdown and compressions test address the performance of the rings controlling compression. The ring(s) controlling oil are not tested by those 2 methods. Both leakdown and compression test are inconclusive for identifying the use of oil.

If you can smell it as you said then you are not burning it you are leaking it onto the exhaust.

Dan

Check the oil filter housing gasket. mine started to leak after 20 years of abuse, which is rare from what I hear. And just for laughs check the the valve cover gasket in the rear to see if it is seeping onto the block as well.