2000 Mercedes Benz S500 Water pump failure

TRAVIS DEBAUN

MEMBER
2000 MERCEDES BENZ S500
0.5L
V8
RWD
AUTOMATIC
168,000 MILES

I've taken my Mercedes to the dealership n had a diagnostic ran on it an received the list my brother is a fine mechanic an told me he can fix it so I purchased a water pimp from napa an he installed it perfectly fine I drove it for maybe 10 miles an it started to squeak an started to over heat so I shut down letting it cool. Brought it back to my brother an had him take it off an took it back, installed the new one we took it for a test drive around the block an it sis it again so we got another water pump thinking it could be a faulty water pump again so napa had one sent from Germany itself my brother installed it while thinking it could be a relay switch I purchased one of those. Car performed great drove it down to southern Oregon a 5 hour drive an everything was fine I get the car back and drive it for maybe 5 miles an my dash says dead battery please service so I pull over and my belt has broken I notice sum melted stuff on my water pump as if something got hot an tried to spin my water pump by hand an was froze up. This is my 3rd water pump that has gone out an can't seem to figure out what is causing it to fail. If you have any idea what this could be please let me know what your thought is on this car.

1 Reply

CARADIODOC

MECHANIC
33,916 POSTS

Repeat failures like this are almost always caused by severely over-tightening the belt. I'm pretty sure your engine uses a spring-loaded tensioner pulley so it would have to be sticking or is rusted tight. It is somewhat common to replace those assemblies when other units are replaced, but check it for free movement by tugging on the belt. It should move freely when you pull hard on the belt, and it must return freely too.

There are a few engines where the belt can be misrouted around some of the pulleys and everything will appear to still work, but the clue is that you have to struggle to force the belt to fit onto the last pulley. If that sounds familiar, check for a belt routing label to be sure it's on right.