explain to me why a engine ground would cause this problem?

The belt drives the pump so is constantly spinning. WOuldnt the faulting engine ground cause other things to go wrong too.?

edit
Ok looked it up.. impellor can become corroded and not cycle fluid properly.. Sounds doubtful cuz its not constant.

Only other thing is radiator cap... which on this car acts like a thermostat too.. i'll try that first.