While I would doubt that I would consider my MB unworthy, or any make of car for that matter, as a result of premature waterpump failures! I do wonder why now what would be the life expectancy of a waterpump?

A waterpump is mechanically simple consisting of a body, a shaft with metal centrifugal impeller, sealed bearing, and a synthetic rubber seal. There is little to ware out.

I have replaced maybe 10 waterpumps in my lifetime and all of those pumps wore out the shaft seal and leaked coolant out the provided drip hole or tube, but only after many years, and many miles!

The only other likely item to ware out or fail would be the sealed bearings, although I have read somewhere about the metal of the impeller corroded to the point it could no longer push coolant.

So what wares out, and why?

The sealed bearings cannot be breached unless the water seals ware to the point of allowing water to enter the bearings and they are sealed as well, and by that time you would have replaced the pump because it was leaking out the drain anyway, right?

So bearing are probably least amongst causes, but could ware out prematurely by not having proper lubrication, or of inferior quality ball bearings (made in India, for example) It seems that the most likely cause for water pump failure is routed around the synthetic rubber water seal resulting from either poor design, or lack of quality of the synthetic rubber material.

Makers of most all anti-freeze claim lubricating qualities, incorporated in their product, also included are anti-corrosion addatives, anti-leak, safe for aluminum, etc.

It would seem there is no pattern to waterpump life, but for example, there is a wide spread between say one's 300E waterpump failing at 50K and anothers 380SL waterpump failing at 225K. If MB uses the same builder for all it's waterpumps, one could assume quality of the componant parts for all pumps to be the same, except for their shape and size applicable to different models of MB engines.

In my opinion, it boils down to the level of quality of the materials used. For example, the builder of MB's water pumps may buy ball bearings next month from China, and maybe a different synthetic rubber seal from Mexico, or maybe Ugoslavia!

A long read, but any comments?

Steve....................