Vehicle: 97 cherokee xj 4x4 4.0l
problem: Have intermittent heat from heater vents and intermittent hot engine light warning. I replaced thermostat with no change. Checked core in/out hoses and consistant heat both sides. No leaks or normal bad core symptoms. No visible water pump leaks or noise. If it leaks could it be possible not to notice? Could it be an internal water pump impellor problem? Or possible radiator problem?

 

Are you sure that your pump is actually pumping? Mine did the same thing a few months ago, the water pump was pumping, but not enough to move the coolant through the radiator. Ended up with a new water pump.

 

How do you know if pump has enough flow? Visual inspection at radiator cap location?