Hello have a 130,000 miles c200cdi 55 reg in good condition. Had it serviced last september at a main dealer.
Oil indicator keeps coming on saying "reduce oil level".
Hasn't got a coventional dipstick so had to waste my time, and get it checked at a main dealer, just in case the sender was faulty.
It was over full, by 2-3 litres.
I can only presume it is diesel entering the engine and "thinning" the oil.
I know the result if i don't change the oil quickly.
I 've been told it can only be the high pressure diesel pump which runs off the front of the engine. Diesel must be getting past the seal and entering the engine.
Has anyone ever come accross this?????
Any posts would be most gratefull.

 

WELCOME to the forums. I'm no diesel guy but for the level to rise it has to be fuel or water entering the system. I'm guessing you already know the oil smells like diesel.
On a gas engine, when they run extremely rich the fuel will make it's way to the oil as well. Seems logical to me that there is an over pressure of diesel making its way past the injectors.
Has anybody checked how long the injectors are staying open and what the system pressure is versus what it should be??

 

When it was mot'd it was running so lean that it didn't register on the smoke test. (common on merc's)
Also if the injectors was entering the combustion chamber i presume it would burn it off. Surely it would be hard to get past the piston rings and enter the crankcase??

 

It happens to gas engines all the time.
Injectors will start pissing, washing away the oil from the cylinder walls which in turns breaks the seal between ring/cylinder wall.
I've also seen where injectors leak into the cylinders after the engine has been shut off causing the same issue.

Without the oil to make the seal, the fuel will pass into the crankcase.

I'm not saying this is your problem and by NO means am I a diesel expert, just giving you some ideas to confirm or check.

I'm assuming by high pressure pump you are talking about the fuel injection pump?? Maybe call Gus at Pacific Fuel Injection (San Francisco, Ca. 650 588-8880) a call, he knows these things inside and out.