On Wed, Jun 15, 2011 at 10:36 PM, YES NOPE9 wrote: > gradually overheats on long drive > no coolant is missing > fan belt is quiet ... does not appear to be slipping > turning on interior heater with fan brings temp down > ( i have only seen water pumps fail by leaking and screeching ) > > What might it be ? =A0 How can I test ? > 99guspuppet Two things come to mind... Deposits in radiator are clogging it, reducing flow rate. Impeller vanes on water pump are corroded away, reducing pressure/force of circulation. How hard is it to reach the pump and remove it for inspection? Lyle --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .