I don't know if there is a specific life of a water pump, but the water pump on my car (see my signature, same engine as yours) went out earlier this year, and in fact, I had forgotten, but that is exactly how it went out.

I was loosing coolant, couldn't find a leak, but I finally noticed it leaking when I let it idle in my driveway. It was the water pump leaking.

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".