Technical Water pump test

Is there a way to test water pumps. When they go bad do they always leak out the weep hole?

 

Normal failures are the bearing going bad, and the seal going bad. Noise and fan looseness and leaking out the weep hole are the usual symptoms.

Occasionally other things happen, such as the impeller loose on the shaft, or rust holes causing leaks.

 

I've seen blades on the impeller wear or break apart to the point they can't really pump anymore.

 

I had one where it had a plastic impeller that came loose from the shaft. It was on a Y block.

 

on a cast impeller, it can rust and corrode/erode to the point that the pump looses its efficiency....
I had a old 6 cylinder, 216 Chevrolet that would get hot...it had a cast impeller that was really rusted thin.
Ordered a "new" replacement pump and the off shore maker had copied/patterned a compromised impeller for the new casting...it wasn't any better than the roached one that was already on the engine....I finally found a NOS one and the difference in the impellers was dramatic and this pump helped the cooling immensely....

 

Besides all the info above, you can visually see in many cars (once the thermostat opens) if water is circulating rapidly though the radiator rather than just moving with convection. Its pretty obvious.
FlowKooler sells a disc you could rivet to the back of an open water pump impeller to allow it to push more water. Its simple and easy to replicate, and they work quite well!
3500-01 was the part number but it appears to have been eliminated when all the new CNC aluminum pump vanes came onto the market. You can still find the images on google.