The problem seemed to come on suddenly. I hardly ever drive this truck but keep it for towing a boat. After starting it, the temperature steadily climbs to max out the gauge. The first few times I noticed it, the temp would drop back down to normal after a few minutes so I suspected the thermostat was sticky. Replacing the thermostat didn't help. I've also replaced the temperature sending unit to no effect. The upper radiator hose didn't have any coolant in it after I replaced the thermostat and ran the engine so I removed the hose from the radiator and filled it with coolant. Didn't help. The water pump has not made any bearing noise nor is there evidence of leakage from the pump. The radiator was replaced about 5 years ago and appears to be in good shape. Any suggestions on how to further diagnose this problem will be greatly appreciated.
My car has 150000 miles.
My car has an automatic transmission.
There are a few things to check over. The water pump produces flow. To check this remove one of the heater hoses (small diameter) going to the heater core. Locate the hose end to a container to check flow of coolant. Test this while vehicle is running, should have flow like a garden hose would have. No flow would suggest water pump impeller is worn. The radiator fins should be clean and undamaged for good airflow through the radiator. Coolant condition can create overheating issues internal to the engine. Head gasket failure can produce pressure in the coolant system that stop the flow of coolant. There are tests that can be performed for this. If you need help having this checked, a certified professional from YourMechanic can come to your home or office to diagnose the overheating problem and advise you on repairs.