I had my thermostat and water pump changed along with my timing belt this week. After the car heats up, the coolant temperature drops just above the 'cold' end of the gauge and stays there. It seems like an intermittent problem, as I've noticed on a few short trips that the gauge shows the temp right in the middle where it should be. Any ideas what this could be? Seems like an odd coincidence that the temperature sensor would happen to go at the same time the thermostat was changed.

edit: even at the cold end the gauge, the heater is still cranking out heat.

 

if your coolant hoses are hot (Upper Radiator, Lower Radiator) and you have heat inside the car...

99% sure you have a temp sensor problem...

odd coinsidence...? Yes, but i've seen even worse with these cars

 

If the gauge jumps from normal to cold very quickly, or vice verse, then it probably is your coolant temperature sensor. You can get one pretty cheap, and replacement is pretty straight forward which can be done in less than 30 minutes.

 

It doesn't jump around quickly, but rather very gradually. I drove 400 miles today to Michigan and back, and I noticed when I first headed out, it heated up slowly to the middle of the gauge. After about 10 minutes, it gradually started to fall to the cold end of the gauge, and stayed there indefintely. It repeated this behavior on my way home. This is why it seems normal on short trips. Still the CTS?

 

If it only drops slowly while driving at freeway speed, (especially in cold weather) I would suspect that the thermostat is stuck open. I would take it back to the shop who replaced it.

 

Took it in today. They replaced the engine temperature sensor (not the CTS). We'll see how it acts on the way home.

 

They replaced the oil temperature sensor? Not CTS? Scratching my head as I am typing this...

 

They called it the engine temperature sensor. I asked over the phone specifically if it was the coolant temp sensor, and he said no.

 

Well I called back and he said there are 2 sensors, one measuring coolant going into the engine and one leaving the engine. They replaced the sensor on the coolant leaving the engine. Fortunately, they didn't charge me anything.

 

Sorry should have asked earlier, but what year is your car? Engine size?