Mercedes 380 SEL

A cheapo fix I used for a water leak when I was a college student years ago was "stop leak". It's intended for radiators, but I recall I used it for a small water leak by the engine.

That I would use that stuff, of course, rules me out as an 'expert'.

If it is the water pump, it usually is the seal of the shaft, because the bearing (bronze or aluminium) is gone. The water seeps between the shaft and housing. Check also the rubber hose from the radiator to the pump - sometimes when older, they show leaks too. For mercedes parts in the US : Eurocar or KWP. A pump is not that expensive for Mercedes.

Troubleshoot! Find the source of the leak before buying parts you don't need. I have not seen a piece of equipment that leaked that source could not be found.

Note we can't see it from here.

Click Image to Enlarge

Without knowing what other water passages are up front, it's hard to say.

I wouldn't count on it leaking all the time. It might only leak when it's hot and under pressure.

I don't think stop-leak will hurt anything, but I doubt it will re-seal a moving, seal surface.

TEST first!!!!!!!

Here's some advice regarding the 3.8 liter engine of that era that has nothing to do with the water pump but could save you a ton if you don't already know. The plastic timing chain guides deteriorate and if it has never had the timing chains serviced, one day you will hear a very ugly noise, a $2000 noise when the timing chain jumps a tooth or two and you bend 4 valves before you can blink an eye. Thus spoke the $2000 voice of experience.

By all means, use a radiator pressure tester. Can be purchased new at auto parts store or on e-bay. An adopter may be required to fit YOUR particular radiator, but they are not that expensive. You can detect water leaks throughout the coolant system, from water pumps to hoses to intake manifold gaskets. I have added food coloring to the coolant system water to help locate leaks. (Color of your choice)

Unless you get a specific answer on this site, you might try web searching Ask.com for Mercedes SEL 1982/water leak. If you are having a problem, there is a good chance someone else has had a similar type of problem, and save you some time trouble shooting, or at least narrowing it to the most common causes that other Benz owners have encountered.

Another site you might try is www.benzworld.org/forums, which is touted as being the premier Mercedes Benz Forum on the internet. Good luck.

Yep! Add water and watch where it is coming from. A flash light (hand held torch) and mirror are all the diagnostic tools you will need.

Hello.I agree with Andy when it comes to replacing parts.Removing what ever is in the way of getting a positive visual of the leak, do it.Buying the correct part to make the repair has always been better for me than the alternative.As to water pumps not leaking after thermal expansion,sure ,why not.In theory it is possible.Experience in these matters however tell me probably not.Hope this helps.

Thank you all for the great ideas even the ummmmmm SNARKY ones.

It is the water pump that is leaking. Though it is still interesting that under power there must be enough heat created to expand the shaft seal and keep it from leaking (even under pressure, I popped the cap to see, boy she blew, i had gloves and a big towel of course) but when the motor cools the seal shrinks and the water come pouring out.

Thanks again for all the great help.