Car has 82,000 miles. Runs good, sounds good, cooling system very stable around 85C, no spikes. I recently changed from green coolant because there was a shiny black floating residue in the coolant tank.

Its still there. Soooo- besides head gasket, where else could black oily residue be getting into my coolant? The radiator hoses arent hard nor is the oil level going down so you could notice. Coolant level stable.

I'll do a head gasket if I have to, but how can I be certain that's the problem? Could oil get in through a water pump bolt or t stat gasket?

There is some sort of Test Kit you can buy to determing if Combustion Gasses have gotten inside the Coolant indicating a bad Head Gasket or Crack.

Is your Oil Cooler Air to Oil or Coolant to Oil?

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84 300D, 82 Volvo 244Gl Diesel

I dont think the om601 has an oil cooler of either sort. There is a transmission cooling circuit in the radiator, but in my experience that results in pink transmission fluid.

There was a recent change to synthetic oil from dino. The residue in the coolant tank is very black and oily, but not milky brown.

What does the test kit look for?

edit: Saw the kit on UTube. Its a sniffer for exhaust. Im guessing I could have an oil seep to a coolant galley and not show exhaust gasses at this early stage. I would really like to know exactly what that residue in the tank is-- thats the test I want.

If the Oil Cooler is cooled by the Coolant the Housing will be near the Oil Filter.
Look on Amazon for Combustion Leak Tester or Combustion Leak Detector. One is aboug $60 and the other is about $30. Once you get the product number you can go shopping and see if you can come up with a cheaper price.

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84 300D, 82 Volvo 244Gl Diesel

If you cannot tell by looking if you have an Oil Cooler or not look at this parts site.

Index to Mercedes EPC Parts Info and Diagrams Everything Benz

The reason I mention the Coolant Cooled Oil Cooler is the Seals on them can leak and once in a while the Crack. I have seen that Happen on Trucks and large Generaltor Engines.

It is also possible for only Oil to leak into the Coolant from a bad Head Gasket or a crack and no evidence of Combustion Gas shows up in the Coolant.

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84 300D, 82 Volvo 244Gl Diesel

DG: I've only worked on om601 naturally aspirated so the oil cooler reference throws me; Im like the kid in the bubble in my own little 190d room.

I looked at the oil circuit in the manual and see no reference to an oil cooler; there is a fuel preheater of course, but Im guessing on this engine the oil filter cannister provides enough surface area to cool things down; its only 72 hp remember. Ive had several engines out on the shop floor and never saw anything like an oil cooler -- boy I would like to have that to fix instead of a head gasket.

Im taking your advice and sending out a sample of the residue/coolant for testing before I tear the thing apart-- I do not want to do this right now.

Im sorry you cant hear this thing run-- it sounds very smooth and has lots of torque. But unless I can find another place to get oil and coolant together, I may have to go for a head gasket.

I've had EXACTLY the same thing in mine for several years now. I've done no testing other than to determine the black residue is not oily. I pulled the coolant tank off to try to get the residue out, but it was stuck good, and I was not able to eliminate it with either solvents or Tide, yet it doesn't seem to accumulate. I've pretty much concluded there is some kind of minor seepage of combustion gas & residue leaking into the coolant either from a small leak in the head gasket or a crack in a combustion chamber. The engine runs fine, has power (such as can be provided by 72 HP!) with no over heating, no loss of coolant, no increased pressure in the cooling system nor any other negative effect. Even in hot weather, 100°+ with AC running, the temp never exceeds 100C and usually runs closer to the 80C mark. There's no evidence of over pressure in the coolant such as you'd expect from a significant combustion leak.

Recently I developed a leak in the coolant tank and replaced it with a new one. Withing days I could see the tank developing the same residue.

I don't like it because it doesn't seem normal, but with nothing negative about the performance I've had little motivation to sort it out and eliminate the 'problem'. I'll be very curious about what you determine yours to be as I'll bet mine is exactly the same thing!

My 84 190D 2.2 is the same way, let us know what you find.

Is it possible that the Black stuff is from the Hoses?

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84 300D, 82 Volvo 244Gl Diesel

I really want it to be from the hoses! There are a lot of internet posts about little black particles in coolant.

But I have oily, smeary something. It floats more than coats; I can clear it up by inserting a paper towel in the tank and wicking it up.


In my case the car has had very little driving in the last few years and I wonder if that's a factor. In any case heres three of us with similiar symptoms. That encourages me to put down the torque wrench and look more closely.

I think what I will do first is drain down the coolant system, get the waterpump and thermostat gasket and look for a place other than the head where coolant and oil get close together. Ideas?

Yep. Possible. But I don't think so. Stock hoses. No issues with them. Mine seems to not be water soluble and it isn't readily visible in the coolant, which mostly looks like water and antifreeze with nothing else very visible. In just about a week after installing new coolant tank you could see the inside of the tank was getting coated with whatever, so it obviously is not oil as I think that would all float on the top surface. I vote for carbon from some source as I believe the coolant hose particles would also float and not coat the bottom or sides of the tank.

I discovered pitch black coolant a few months back, I was sure that the engine was toast. But then the power steering pump pulley finished wearing a hole in the upper hose, and I knew where it was coming from.

Water Pump Seals on US Cars were somtimes made of a brittle Black carbony sort of stuff. But, none of My older USA Cars had a Coolant Recovery Tank so I can't comment on balck particles

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84 300D, 82 Volvo 244Gl Diesel

As things stand now I only have a thin smear of oil in the coolant which I am going to monitor carefully. Seems like the thing to do is carefully go over the coolant system and look for problems. In my case everything seems to be functioning properly, although its been so cool here lately its hard to stress the cooling. Given the relative pressures involved, it seems like coolant in the oil is unlikely here.

If anyone thinks of a gasket that shares oil galleys and coolant I would be all over that. I had a HG go out once and it was dramatic, so if suspect I will have to address it. Space is very limited around this engine, so its a time consuming job, but not terribly hard.

The head gasket does that.