water pump failure?

[yogib123]

hiya everyone, ive had a new engine put in my corolla recently and today the water pump seems to stop spinning when i rev it up a little, when driving it seems to be fine but not sure what could cause this as the pulley doesnt stop spinning only the attached bit (not sure on the name) but it sits on the pulley, i can move it freely with my fingers without the engine running aswell, any help would be appreciated 

[Mooly]

This might sound strange but your description sounds more like the aircon compressor. The bit that sits on the pulley would be the compressor clutch and yes it will turn freely when the engine is off.

If the water pump stopped spinning while driving the engine would overheat very quickly indeed.

[yogib123]

seems i am what is known as a moron, got worried over my car working lol, thanks for your help anyways