Hello all. I have a 2002 626 4 cylinder that is cooling fine at idle. When driven, the temp gauge rises to the hot level. Then it drops back to high side of gauge but not hot.normal operating temp. It takes i while but i can feel heat coming out of heater. I have installed new thermostat. There was crud in the bottom of radiator reservoir tank. No coolant just water when i drained radiator. Also when hot, the temp gauge drops when pressure is released from radiator cap. Any suggestions? Partially clogged radiator? I am going to get a thermometer and check areas of radiator for hot or cold spots today. Or water pump? Faulty sensor? Any ideas would be helpful. Thanks for your time in advance!

 

Get the radiator flushed professionally, also remove the thermostat, drain the system, flush the rest of the cooling system with a garden hose in both directions.

Fit a genuine thermostat & genuine radiator cap, fill with coolant & road test.

 

Copy that. I did shoot the radiator with a temp sensor and had a spot that was about 15 degrees warmer than everywhere else. Will pick up a new radiator cap and flush rest of system. Fingers crossed! Thanks for the input.