Possible breech in the head gasket between the oil feed passage and number one cylinder. There are other possibilities of course but I might check for this first. Except you mentioned the change in the fuel color.

The chances of actually needing a new engine are very small. Could be a failed turbo seal if your model has one. Again that does not change the fuel color.

In an event the problem should be identifiable without a great amount of effort.

The usual test is to remove the first cylinders glow plug and see if that cylinder is spitting out oil. Also comparing the appearance of the first and second cylinders injectors. In your case the evidence points elsewhere.


If you would like a good mechanic to look at it. There should be someone within reasonable distance that local Mercedes owners can recommend. I might even ask a local Mercedes dealers if their is an independent mechanic they can recommend.

Although it is usually smarter to go with what defect appears obvious. It sounds like you are saying the fuel entering the lift pump is clear and the fuel exiting it is black. If I understand that right I would need to find out what I causing that. It of course should be clean fuel in and clean fuel out.

An almost impossible symptom but if you have it. It has to be possible. Normally there is a small o ring in the lift pump that seals the crankcase oil from contact with the fuel. Actually the engine oil lubricant flowing through the injection pump. If that is bad the engine oil usually gets diluted. Not the engine oil that is very black in these diesels getting into the fuel. This is a little different than normal but does not sound all that serious. Is that problem you know of the issue? It to me is the first thing to solve and it just may be the issue. I am a little bit surprised it was observed.

I have never owned a 602 engine or worked on them. They have a different lift pump than the earlier cars. How different internally I do not know. Obviously it has to be doing fundamentally the same job as the earlier lift pumps. All I am really cognizant of is the engine oil should not be showing up in the output of that lift pump. If the engine crankcase breather is that obstructed to be forcing oil into the lift pump. I think the engine would shut down.

So if you verify that what you mention is occurring. Your model lift pump is not rebuldable like the earlier versions. Perhaps getting a used lift pump from a member is not a bad ideal. You can change it out yourself as it is pretty easy. You may want to remove it and see if the casting is cracked. There is an O ring that services the push shaft that you might be able to replace. It is not a special exclusive part. It will just be an O ring. Again this may not be the problem you have. It just might be at the same time. What is absolutely positive though is clean fuel should not be entering the lift pump with black fuel coming out.

There also is a fuel pre heater for the fuel after the lift pump. Bypass that to see if that is where the engine oil is getting in. If the engine oil temperature is used as the pre heating medium for the fuel. That is where the problem should be. Sorry about the long drawn out post. If the pre heater is breeched internally. When you bypass it engine oil will probably come out of it. I think you can solve this issue overall yourself. To me it just fits what you observe.

I will not go into all the reasons I think so. I could be wrong. Let us know how you do with the problem.