Water pump or Thermostat failure? 325CI

[Cabe]

My 01' 325CI Suddenly over heated.... and blew a crack in the Coolant expansion tank. I've replaced that with no apparent problems. Although, the car still over heats but only under a load (not at idle) It appears that the coolant is sitting stagnant and not flowing... Would this more than likely be the thermostat or the water pump??? Any help would be swell...

[WarrenBrown]

My guess is the water pump has a fiber impeller that disintegrates. Replace the thermostat and water pump. If the car has a plastic thermostat housing then that should be replace with an aluminum one from an aftermarket company. I assume it is the same part as an M50 engine.

Warren
91 318is
95 525iT

[winfred]

way different, the m54's a bigger pain, hard to say whats wrong, i've seen year old factory radiators collapse internally after a overheat that was not bad enough to dammage the motor

I assume it is the same part as an M50 engine.

[Cabe]

Thanks for some thought. For some reason I think it's the thermostat because it doesn't heat up at idle so it must be getting just enough water thru to keep it cool until you put it under a load. I guess I should just change the water pump too as long as I'm in there. Just not sure how much more work that will be because I haven't looked in the manual yet and I'm not a certified BMW mech. Thanks