Originally Posted by
solaratomic
The primary symptom of water pump failure is leaking out the weep hole (bearing/seal failure). Only in EXTEREMELY high mileage vehicles have I heard of the impeller vanes "grinding" off. It sounds like you're having a problem with heat dissapation. Change the thermostat then you may wanna have the radiator rotted out or replaced. After eliminating the basics then you may wanna start looking more in depth at you motor. Good Luck.
There are quite a few cases of the early 6.0L water pumps breaking off their plastic fins or the entire impellor coming off.
I think a coolant system pressure is the best test. I am just now considering the best place to get the coolant pressure reading so I can get some data. The easiest place is on my coolant filter, but that is at the end of the line. The best place is probably at the block plug - I just do not want to drain my system completely (at least not so soon after flushing it).