Pressure release cap. Mercedes OM636.

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Mickmack
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Pressure release cap. Mercedes OM636.

Post by Mickmack »

Hi. Can anyone tell me the rated pressure for the cap on the Bowman Heat Exchanger as fitted to a Merc' OM636. When I bought Septimus, a Westerly Medway the head on the original engine was cracked. I have replaced it with a re-con' head, new gaskets etc and it now runs like a sewing machine. The problem is as soon as it starts to warm up under load water starts to come out of the overflow, not under high pressure just a steady dribble. The cap fitted whilst looking in good condition has a very soft spring behind the seal. Absolutely no sign of gas leaking into coolant, or of water in oil so I do not think there is a head gasket problem. More a case of too soft a spring in the release cap. Thanks in advance. Mike.
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Re: Pressure release cap. Mercedes OM636.

Post by Vegable »

Hello Mike,
A wander into Halfords might be an idea to see what sort of pressure variations radiator caps have...or may be have a word with your local garage mechanic. However I'm wondering if that is the answer to your problem. Have you thought about fitting an expansion tank? All it needs is a bit of tubing from the overflow pipe into the top of a plastic milk bottle (or similar) with the tube going all the way in to the bottom of you chosen container, which will have some water, say 3" or so in the bottom.
It might be that the leaking water is just expansion when the engine water warms up. The expanding water will go into your container and then when the engine cools down the contracting water will suck back out of the container back into the radiator. It's the same system that you'll have in your car.
If the expansion tank fills up then I'm afraid you still have serious engine problems.
Mike
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Tony Wardale
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Re: Pressure release cap. Mercedes OM636.

Post by Tony Wardale »

I had a 636 for about 30 yrs and got through 3 Bowman Ht Exchangrs in that time . The first was an old type and an elbow fails due corrosion, the second
one was an own gaol as I did not use a 50/50 antifreeze water mix .I did lose water until the rubber covers were tightened up .The Heat Exchanger fed a calorifier and that had an expansion tank in th circuit.

I hope this helps

Tony
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