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Originally posted by trashline:
this topic is more for a friend... he says when the car warms up the heat works great and the running temp of the car is fine even if he revs it. as soon as he drives the heat gets cool and the running temp goes down. i told him it might be the thermistat what do you think?

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Water running through the inside radiator comes directly from the main rad, through the pump.

Sounds like to me there is NO thermostat on this engine (that's really bad for the engine BTW !!), now if there is one it could be stuck open.

If the thermostat is not opening properly, water will be too cold out of the pump and that may cause your problem BUT you would soon see it on the engine temp gauge ! It'll go up really quick ! So I would rule this one out.

Assuming that the external temp isn't super cold, the next thing I would suspect is a clogged internal rad or stuck/broken vent doors & cables inside the heating system