temp gauge - engine temp sensor
 

This morning I noticed that as soon as I started the car Temp gauge was showing normal working temp and radiator fan was on. Car sat in garage over night and there is no way engine stayed hot for 10 hours. Is this mean that coolant temp sensor is bad?
Also battery died yesterday and I replaced it. Not sure if this is connected.
Any input is appreciated.

If you unplug the sensor what happens?

We'll see tomorrow. It's my day off so I will have time to deal with it.
Car has about 240K on it so I will probably replace sensor and thermostat

When unplugged sensor, temp was showing that engine was cold and raised slowly to normal but fan was on all the time even with engine off.

sounds like maybe the car put itself into limp mode. disconnect the battery for half an hr or so then reattach and see what it does.

I did it and no change, it still shows that engine is warm when start the car. There is no difference in car performance, still drive like champ

It is showing right temp now. It did it by itself, not sure why or how it was reading wrong temp. but since yesterday everything is back to normal. Anyways, going to replace thermostat and sensor soon.

Today I replaced ETS and thermostat and upper hose. I was amazed how clean coolant was in there. 15 years old coolant looked like brand new. It took about hour to do the job

the reason it was so clean is because it was distilled water NEVER use tap water :D