M103 coolant leak - hard to ID - Mercedes-Benz Forum
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post #1 of 14 (permalink) Old 11-06-2016, 11:45 AM Thread Starter
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M103 coolant leak - hard to ID

It seems like this is near the oil filter, and it looks like there may be a loose hose connection, but MAN is it ever hard to see.


Anyone else ever had a leak there? Is there an easy way to get in there and ID the leak?

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post #2 of 14 (permalink) Old 11-06-2016, 10:51 PM
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As you say in the video that’s probably not the head gasket … that’s usually from where the heater hose is connected to the cylinder head. There’s a pipe to which the hose is connected (the one with the lifting bracket welded to). That pipe sticks about an inch or so deep into the cylinder head and there’s an o-ring sitting on it inside the head which after 30 years of thermic stress is sick & tired.

The friendly people at the MB delership will probably give you that o-ring without charge … if not tell ‘em that in Germany they usually do … lol.

But be careful with the Allen profile of the two bolts which fix the pipe with the lifting bracket to the head .. they’ve probably been sitting firmly tightened in there for three decades... use a quality tool.

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post #3 of 14 (permalink) Old 11-07-2016, 11:47 AM Thread Starter
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I guess I need to take a look at some diagrams of the cylinder head. It does seem strange that the oil filter is so far off to the side near the intake manifold. I guess this is my first m103. So... new stuff to learn.

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post #4 of 14 (permalink) Old 11-08-2016, 03:46 AM
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HD Your right ,after i replaced my water pump last year i was still loosing coolant .And that was the place it was getting out .Then after going along the join of the head to the block at the rear of the engine found its way down, and dripped off the transmission housing and on to the floor. Hard to get this part off if the three cap screws are worn on the heads .I needed a good drift to get mine out .Then replace them with hexigon bolts . O ring was fitted along with sealer , as a second back up.
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post #5 of 14 (permalink) Old 11-08-2016, 05:16 AM Thread Starter
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Great discussion here, and thank you all for this input.

Could I be wrong in my thought that the leak is coming from this apparently loose hose fitting?



It is hard to see if that fitting is attached to this heater hose.

^^ see the hose coming from the firewall that goes down on the driver side of the oil filter.

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post #6 of 14 (permalink) Old 11-09-2016, 03:32 AM
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Quote:
Originally Posted by Fonzi View Post
... Could I be wrong in my thought that the leak is coming from this apparently loose hose fitting? ...
You need a small mirror and a flashlight to have a closer look. However, I want to point out that the o-ring I mentioned, if it’s leaky, can make the hose connection to the pipe look like the culprit.

A leak that becomes visible 30 - 60 minutes after the hot engine has been switched off rather than when the engine is still running or just been switched off, would increase my suspicion.

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post #7 of 14 (permalink) Old 02-02-2017, 11:42 PM Thread Starter
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M103 coolant leak - hard to ID

Learning that I should be able to get all the paperwork to make this fairly decent car 100% legal, I decided to revisit this issue. I crawled under the car, and it's pretty clearly not coming from the head gasket. I'm sticking with my initial focus of the hoses that provide coolant to the oil cooler. They are hard to get to, so I will probably wait until the car passes inspection to really fix this, but I decided to investigate and put some good coolant in before the deep freeze we are about to have. (There was a coolant bottle in the trunk full of water when I bought the car which got me worried that there's a lot of water in the system that could freeze.)

I crawled under...


I can see a hose that's filthy, but also seems washed clean so that you can even see the lettering on it. [edit: I think it actually says "103" on it, dead center in the pic. Can you see?] I think that's my culprit. But how to I get to that SOB.



And if you are like me, concerned that's not even a coolant hose in the EPC, I verified that the pipe from the water pump goes to the oil cooler on the filter too:


So I'm thinking that the time to change those hoses and clamps out would be when doing the next oil change. But will I be able to get to them under the intake manifold? Or will I have to remove that too?

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Last edited by Fonzi; 02-03-2017 at 05:28 AM.
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post #8 of 14 (permalink) Old 06-24-2019, 01:57 PM Thread Starter
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I finally took the time to get to the bottom of this one. I got tired of it peeing everywhere I park it, and had it at home to swap the wheels with my 500sec. Then I'd wanted to take the belly pan from this car too. So I popped it up on jack stands to get to the bottom of this. I will post pics of the offender in the next post. It seems there was a cap in place of the line that should go from the driver side of the oil cooler to the water pump. That cap failed.

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post #9 of 14 (permalink) Old 06-24-2019, 02:50 PM Thread Starter
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Maybe this will best describe the issue. I need to get in there and see if the “mechanic” that did this modification used the same type of cap on the other side.



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post #10 of 14 (permalink) Old 06-25-2019, 06:33 AM Thread Starter
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How does oil cooler to water pump pipe connect to water pump?

I would really like to confirm that the water pump connection is not going to also fail as soon as I put a new plug on the oil cooler. I don't see the pipe. So I assume that it is either plugged, or the water pump that was used (presumably when the head gasket was replaced) is a different water pump that does not have the connection for the oil cooler.

Does anyone know if there are m103 engines that do not have the oil cooler? I guess I can check the EPC for that.
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