Bowman heat exchanger leaking on Mercedes OM636

[kingsebi]

The Bowman heat exchanger on my Mercedes OM636 leaks salt water through the overflow line at the pressure cap. It’s a steady drop. I ran the engine until warm, shut it off and removed the cap with a cloth. No hiss, so I’m positive there is no pressure in the internal cooling circuit. I understand that is the reason why salt water is forced in. I had the piece where the pressure cap goes on break off from the heat exchanger two years ago and glued it back on with cold weld epoxy. It used to be fine, then it broke off again and I glued it again. I will try to glue it again as it’s my primary suspect. I will also check the rubber end caps and the jubilee clips.

My question is: I’m at anchor right now and not close to the next port. If I don’t find the leak, do I risk to damage the engine running it like this? It runs fine, the temperature is normal, but I’m worried about salt water rushing through the internal cooling circuit.

 

[penfold]

You have a coolant circuit full of salt water, I'd suggest draining it and flushing it with copious fresh water, flushing and changing frequently until you can get to somewhere you can investigate the leak, as having salt in the coolant circuit will be merrily depositing scale and causing corrosion.

 

[kingsebi]

Thank you for confirming what I thought.

 

[rogerthebodger]

The O ring on the end caps has failed and allowing sea water to mix with the fresh water coolant.

If there is a leak out of the end caps like I had the aluminum could have corroded , I had to have mine rewelded,

There could also be a leak in the coolant tubes inside the heat exchanger

Header Tank Heat Exchangers

 

[kingsebi]

Thank you I will check that.

 

[yanay]

The Bowman heat exchanger on my Mercedes OM636 leaks salt water through the overflow line at the pressure cap. It’s a steady drop. I ran the engine until warm, shut it off and removed the cap with a cloth. No hiss, so I’m positive there is no pressure in the internal cooling circuit. I understand that is the reason why salt water is forced in. I had the piece where the pressure cap goes on break off from the heat exchanger two years ago and glued it back on with cold weld epoxy. It used to be fine, then it broke off again and I glued it again. I will try to glue it again as it’s my primary suspect. I will also check the rubber end caps and the jubilee clips.

My question is: I’m at anchor right now and not close to the next port. If I don’t find the leak, do I risk to damage the engine running it like this? It runs fine, the temperature is normal, but I’m worried about salt water rushing through the internal cooling circuit.

I have exactly the same scenario with the filler neck breaking twice. My heat exchanger expels water while running at normal temperature.
HowDid you fix it?

 

[kingsebi]

I glued it with cold weld epoxy again. Funny you wrote that just now. Yesterday the water elbow (where the temperature sensor connects) on my motor corroded through, all the cooling water flushing out. Aftermath of having salt water in the circuit I suppose. More cold weld epoxy…

 

[yanay]

Did you fix the overflow issue? Check the end cups? Exchange the inner tubes in the heat exchanger? Did you run it for long with salt water and where did you let the overflow go?

 

[kingsebi]

Yes I fixed it. I reglued the filler neck. I took out the tubes and they looked fine. Some of the jubilee clips were a bit loose and I tightened them. I don’t really know what fixed it.

After all that I still had water bubbling out from the heat exchanger mounts, but this problem fixed itself. I think it was due to too much liquid in the heat exchanger and with the right amount it didn’t happen anymore. If that makes sense!

I didn’t run it like that for long, only for short times during a week or two while I was trying to fix it. Draining and replacing with new cooling liquid as often as possible. Still too long, judging by the corroded water elbow. The overflow I directed into the bilge.

I hope this helps. As you can probably tell I am very far from being a mechanic and if you keep having problems my advice would be to get in touch with Manfred at Westfield 4x4 in Lancaster. He knows everything about the OM636 and is very helpful.

 

[yanay]

Thank you, Yes this is very helpful. I want to eliminate the option it’s a hole in the inner tubes. I’m in touch with Manfred. Just trying to understand exactly- the overflow stopped but not by tightening the hose clamps (which jubilees- on the end cups?) or extracting and installing the inner tubes but continued and only stopped later for unknown reason? Was taking out the tubes difficult? it comes out of the front of the HE? Were there gaskets, o rings or other destructible parts? Where is you rwater lever now in the HE when running the engine? What did you use to channel the overflow from the little expelled water hole in the filler neck? Indeed about a year ago I emptied the HE and refilled it with half rain water and half coolant. I remember the amount that went in was higher than expected. Should’ve been 4 liters. The engine run nice and cool since, for 30-40 hours with no overflow but last time I run it at anchor it overflowed and continues to do so. I don’t see any leaks or cracks on the end caps, although the aft hose on the water outlet ( it’s a 3-hose attachment going from the aft of the HE to the exhaust) was leaking a drip from under the hose clamp on the exhaust but stopped now. The filler neck cold weld fix lasted about 1.3 years. I just re epoxied it for the third time. Any relevant information will be helpful. I’m at anchor and must leave on 200nm leg in less than a week. Worst case scenario I would probably run it with the overflow and keep an eye on the temperature, wash the HE with fresh water frequently.I just don’t want all this hot maybe salty water running down on the fuel pump for hours.

 

[kingsebi]

Taking out the tubes was easy, they came out at the front. I tightened all the hose clamps on the inner and on the outer circuit. I think the hose clamps on the rubber end caps are particularly important, on each one there are two clamps, one seals the inner and one the outer circuit so they don’t mix. I don’t remember any gasket or other parts inside. My water level: When I dip my finger in it comes out wet up to the first joint. This seems quite low to me, but the motor runs at normal temperature and if I put more it will start to bubble at the heat exchanger mounts. I plugged a flexible tube (I think a length of fuel line) on the small nozzle on the filler neck to direct the overflow away from the motor into the bilge as the salt water was starting to corrode the manual fuel pump and injection pump. Not good!

I think the drip on the aft line is not a problem for the inner circuit as it comes after the heat exchanger.

I think the only problem is that the salt water will corrode things. Temperature wise it should be fine - at least was for me. And things don’t corrode so fast. But eventually they do.

Happy to hear you are in touch with Manfred. I hope you fix it before you go! Good luck! I will try mine tomorrow with the newly cold welded water elbow…

Edit: I was just thinking, your problem could also be a faulty filler cap that doesn’t keep the pressure. Happened to me before.

 

[yanay]

Installed new end cups with new jubilee clips and hi temp silicone and the problem stopped

 

[kingsebi]

Great, have a good trip!