Verify if the water pump is pumping
One way to test for a bad water pump is to squeeze the upper radiator hose when the engine is hot and idling. Careful, because the hose will be HOT! If you do not feel much coolant circulating through the hose when you rev the engine, the pump may be bad. The other cause might be a bad thermostat that is not opening properly (remove and inspect the thermostat), or a clogged radiator.
Pressure test the R/Cap
Feel across the front of the radiator should be evenly warm-any cold spot could be clogged up.
Thursday, September 25th, 2008 AT 3:41 PM