...I have an '87 300D 6 cyl Diesel w/14 head...I recently noticed the temp gauge at 120C at an intersection (air on)...I shut it down immediately...I let it cool and added about 2 quarts of water...When I got home I noticed the electric fan would not come on unless jumped...I can see that coolant is coming from the underpan but have not had time to pull the pan to localize the exact leak point...It is losing about a quart and a half of coolant in 50 miles...I can smell coolant inside the car when driving...

...I'm thinking it could be a heater core,...but no wet carpet???...Heater hose connection???...Or worse case scenario a cracked head and the cooling system is over pressureizing...(no signs of water in the oil though)...As long as there is adequet coolant it does not overheat...

...I do not want to waste any ones time but I am completely unfamiliar with these cars...I have a '79 and an '80 300SD,...but entirely different cars..

...Any help or direction would be greatly appreciated... Thanks Willie

I'm afraid that it will be impossible to find your leak from my keyboard, and that is the next logical step. Remove the belly panel, find the source of the leaking coolant.

The head should be fine, but next time it's running hot, don't shut it down, cool it down with the heater and easy driving. Heat-soaking the head didn't do it any favors.

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Gone to the dark side

- Jeff

...Thanks...I tried to cool it down by shutting off the air and easy driving...I forgot about turning the heater on...At that point I was afraid of having lost a much larger quantity of coolant and opted to shut it down...I will pull the belly pan asap...In the 10K mi. I have driven the car it has always seemed to run on the warm side about 100C,(I do not know what that converts to F???)... is that normal???

No, it's not optimum. Do you live in a warm climate? Mountains? For some, it is normal.

Although I'm a several-times OM603 owner, most of us don't come here to the gas side, and this question is answered almost weekly in the summer over on the diesel forum. It might be prudent to re-post over there, you can even delete this thread and start over, you'll get a lot more direct experience very quickly there (none of mine have ever run warm).

The radiator can be blocked internally, or failing.
The space between the A/C condensor and radiator is often full of junk at this time/mileage
The fan clutch might be failing
The water pump might be failing (pitted from non M-B coolant)
The head might be failing.

This in addition to your known leak, but the leak is the first thing to cure.

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Gone to the dark side

- Jeff

shouldn't this be in diesel discussion?

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1983 240D 3.0T 4-speed manual, now sold

1989 Subaru GL Wagon 5-speed Touring Edition

...What a great Forum...I found my water leak after removing the belly pan...I am not to sure which hose was leaking as any hose clamp that I could tighten,...I tightened...I also found the electric fan disconnected...

...I found a diesel leak which I have addressed in the diesel section...

...Having had a 6.3,...a 280SE 4.5,...a 280C,...a 280,...and two 300SD's,...I certainly wish the forum had been around in years past...


Thanks again Willie

Happy to hear you've fixed your leak, and the issue with the fans (which are also for the A/C).

However, the engine is still running on the warm side, which could spell an early death for the original head, I'd check the items mentioned above.

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Gone to the dark side

- Jeff

...I spoke to soon apparently I have only slowed down the leak...There is one hose I could not reach...I will have to remove the overflow resevoir or air filter box to get to it...

...With the aux fan now operating,...The running too warm issue has lessened greatly...

...If the last untightend hose doesn't do it,...I will next try changing the radiator cap...It is losing aproximately 2 quarts of coolant in 100 miles...

The aux fan shouldn't be doing the normal cooling, the clutch fan should. It might not be working.

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Gone to the dark side

- Jeff

...The aux fan only comes on when the air is on...I have not studied it enough to see if that is all the time with the air on...(just analized this and the aux comes on intermittently)

...Now with the car up on ramps and ideling with the air on,..there is cold water dripping down the drivers side of the transmission...I am assuming this is from the AC drain???...

...On the passengers side of the transmission,...there is hot water dripping down...My thinking is that it could also be from the AC but is being warmed by the path it is taking down the transmission???...

...I have now pinched off the water line going into what I believe is the heater valve...(In the encloser behind the overflow tank)...The warm water running down the passenger side has slowed down???...

...Does anyone know how I can access the heater core to check it's respective connections and the core for leaks??? Thanks

A/C drain on the cold, not sure about the warm, does it smell like coolant or feel slippery like coolant?

Heater core leaks can be a pain, buried under the dash and only accessible by removing the dash.

The aux fan should come on low with the A/C via the pressure switch and a resistor near the accumulator/dryer, ceramic in the '87. They should come on high with the coolant temp, 212F/100C is my memory on that, but I don't remember for sure.

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Gone to the dark side

- Jeff

During my testing I have been refilling it with water...I don't think there is any coolant left in the system after my tests...

...With the heater hose pinched off I drove the car fairly hard for about 25 miles...It lost about 1/2 pint of water...

...I then put in a tube of alumaseal and drove on mountain roads for about 50 miles,...with the heater on full blast...It lost another 1/2 pint???...It is losing far less than it was...

...Tomorrow I will get a new radiator cap...BTW there is oily black residue in the resovoir???... Thanks again

Black oily residue, search "14 head" on the diesel forum, could be very bad. Could be losing coolant into the cylinders through a crack in the head, the problem was cured after the 1987 cars in later head revisions.

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Gone to the dark side

- Jeff

...The upper radiator hose was soft before I started it this morning...The black residue was no longer there...I drove the car normally for about 20 miles this morning and did not lose a drop of coolant...(Did not run warm)...I replaced the radiator cap after this drive...I will give it a harder run today...???...