Why does a water pump in a car go bad?

Answer 1

Bearing wear (due to normal friction) or hardening of seal (also normal).

Water pumps bearings move so they wear out like all other moving parts in your car eventually will. The seal is made of rubber (really good rubber) so it will eventually harden and shrink and fail.

Things that are likely to contribute to early failure of water pump:

-Old or contaminated anti-freeze.

-Overtightened belt (assuming water pump is belt driven).

-Excessively high speed operation (as from prolonged high speed driving, improper transmission shifting, lots of hard acceleration.

-Pump wasn't well made.

-Excessive vibration (from old multi-V belt or engine or belt-driven things.)