New member...thanks for your upcoming patience with my post..I have a 1992 E300 2.5 turbo diesel...beautiful car...bought last may with 83000 miles..one owner for 79000, second for the rest. I have driven the car 8000 miles until the beginning of summer. Driving home one evening suddenly a huge amount of smoke became visible in the rear view, about one mile from home...Parked it, took it to one shop with a bunch of gasoline germans. He said I need a new engine. I called adsit.com to inquire concerning a rebuilt engine and the gentlemen in this department said he never seen anything happen to the bottom end of these engine with 91000 miles. Also stated that an injector problem will mimic a rod knock...at idle it sounds ok most of the time then a quick knock or two that sound not good but you also notice the fuel entering the fuel transfer pump to be clean and the fuel coming out to be real black going up to the canister fuel filter..The adsit.com mechanic said to crack the injectors to determine the question of rod failure, I guess!....was wondering how oil could enter the fuel? ..my abilities lack much diagnostic talent but can turn a wrench fine...I drive a 15 liter cummins at work, the benz is my third personal diesel alongside a 1989 Ford 7.3, with the recent highly regretful departure of a 2010 VW tdi.....Any ideas, suggestions, etc would be appreciated...This car is almost like new everywhere else.I would put an engine in it if I was sure it needed one....The southern tip of ohio is lacking in diesel mechanics who are interested in examining this car.....Anyway, thanks again for any ideas.....oldgold

Replace or test the injectors with a pop tester. Never heard of a bottom end failing on a 602

Replace or test the injectors with a pop tester. Never heard of a bottom end failing on a 602

what is a pop tester???...Is it the same procedure as cracking the injectors?....I know about this procedure....Also, do you think several cans of a diesel purge would give me any informative results??/.I could replace injectors but hoping for a definitive test before buying them....thanks again for the info...

Does it have a rod knock sound?
602's are known to have head gasket failures. Bad turbo seals will allow engine oil into the intake.

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92 e300d2.5t
01 e320
05 cdi
85 chev c10

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.

[QUOTE=oldgold;3841921]what is a pop tester???...Is it the same procedure as cracking the injectors?....I know about this procedure....Also, do you think several cans of a diesel purge would give me any informative results??/.I could replace injectors but hoping for a definitive test before buying them....thanks again for the info...[/QUOTE


A pop tester duplicates the hydraulic pressure the injector is normally subjected to. How the injector acts with this is a pop test basically. I would forget the diesel purge for now as well.

Plus do not buy injectors to replace the ones in your low milage engine. I suspect they are fine anyways at this point. I like to or prefer to spend money only where it is needed.

The people you called about a rebuilt engine treated you well. Look up reviews of that company. Hopefully they are better now than they have been.

Also nice to see new people on the site. If you own an older Mercedes diesel you are at the right place.

A pop tester is a hydraulic gauge on a hand pump. You use it to see if they spray properly. Alternatively you could order 5 new injectors from a source with a generous return policy and see if that cures the issue.

The real name for the pop testers is a Diesel Nozzle Tester. You can look on eBay to see what they look like.

The O-ring that the other poster was speaking of can cause Oil to mix with the Fuel.

The Injector Cut Out test that was spoken of is while the Engine is running you loosen one of the Injector Line Nuts (this cut so off the fuel to the Injector because the fuel squirts out, a little messy )and see what effect it has on the engine. The tighten it up and go to the next Injector.

If a Cylinder is making a knocking sound cutting off the Fuel by loosening the Injector Line Nut will stop the sound. And that identifies the problem cylinder.

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84 300D, 82 Volvo 244Gl Diesel

Don't ask mechanics who are not familiar with MB diesels to diagnose or guess your engine issues. In this case calling out a rod as source of knock... when much more likely problem is injector.

There is a definitely different approach to diagnosing and chasing down issues on these engines that no equivalent procedure on gas cars.

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Cheers!
Scott McPhee

1987 300D

The fuel pre heater is using the engine coolant for function. So engine oil is not mixing with the fuel there. Well if the oil under pressure is higher than the internal lift pump pressure it can flow into the lift pump. If the O ring is bad.

My guess is the available oil pressure lubricating the injection pump is higher on that series of engines in the injection pump. Basically less lubrication flow restriction than the earlier injection pumps. A heavy flow meaning more oil pressure is present perhaps.

That is only a guess though as on the earlier engines the fuel tended to flow into the engine diluting the engine oil in the process. The engine oil level would rise.

With the black appearing fluid logically being engine oil added to the fuel. A smoky burn is to be expected. That used engine oil burns dirty is well known.

If you had not mentioned the change in the fuel color. Or it was not observed and the signifigance of it understood. You could have undergone a horrible experience finding your issue.

My overall point is there is no way to expect to see the color of the fuel changed in the way you describe. As a normal situation.


I am heavy on diagnostic testing. If you disconnect the output line on the lift pump. Collect a little fuel by cranking the engine. With the shut off tied down on the injection pump.


So the engine does not start. It probably will not anyways. If that fuel sample is darker . Remove the lift pump to see if you can change that o ring in that model of lift pump. You probably can.


Also if it turns out to be the issue. Change the engine oil as some fuel may have thinned it.


It sounds like you have located a really nice example of the model.

Well a large increase is smoke can be from several things (bad injector, oil seals in turbo failing, head gasket failing so that oil goes into #1 cylinder). We'll need more info to help you diagnose it. The good news is that none of the three things that I mention would require an engine replacement.


A really great way to get help here would be to take a video of the car with the engine running, so we can see and hear what you are talking about. Post the video on youtube and link it here. Show us the smoke, let us hear the engine noise as you rev the engine up a little, let us see the engine at idle and at a higher RPM.


Please provide any other information you can, including any work that was done to the car before the smoke event. What does the engine sound like now compared to before? Any loss of power? What is the engine oil level like, has it dropped or increased? Are you still driving the car since this happened, or did you park it until you could fix it?

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Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC