I have a 1986 300E in very nice condition with over 250,000 miles. It has a slow cooling system leak. I used a cooling system pressure tester yesterday. The system held steady at about 17 psi (1.2 bar) after I replaced the two main hoses and clamps (that were overdue anyway).

Then, when I ran the engine, I had a small leak that appears to be coming from somewhere near the water pump. I cannot see any leak around the pump shaft and, after removing the air cleaner, I cannot see the source of the leak. It is not the transmission cooler hose. I am pretty sure that it is the water pump, but I can't prove it--and it is the original pump (unbelievable, but true as I have all of the records).

Has anyone seen this before? Should I just suck it up and replace the water pump? It looks like a pain to do; that's why I would like to prove it first.

Thanks in advance for any help.

Brent Smith
Atlanta, GA
1986 Mercedes 300E
2003 BMW 530i
2003 Boxster S

This will probably be your problem. See the foto. You will probably need a new water pump. There have been a few discussions recently on M103 water pump issues and the replacement thereof.

There is special dye that you can buy that is visible with a UV light. This might be the easiest way to determine if you are having trouble.

But I agree with the above -- That is the most common place. Same place as mine.

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