2000 TL - 200,000K+.

Just replaced the thermostat. Put the old one in a pot of boiling water and it opened right up. So the “overheating” wasn’t from the t-stat. The temp gauge will literally top out....past the red. But there’s no signs of it actually overheating other than the gauge. Radiator is full. Reservoir has fluid in it. Top hose is hot when I check after driving, but the radiator is cold. I’m thinking water pump, but would be interested in people’s thoughts. When I start the car it immediately goes to the normal operating temp on the gauge....but it should be registering cold. Then in about 5 mins it pins it high.

 

If the engine is truly not overheating, then it sounds like you may have a bad temperature sending unit.