Coolant temp indicator acting weird

[sbihue]

Hi,
I have a strange problem with the coolant temp indicator on my 90/525. When i start up the car in the morning, the engine warms up and the temp indicator moves into the middle. However after a while, the indicator falls into the blue zone. It remains like that until i stop the car at a stop light for approx 30 seconds or more. At that time it again creeps back into the middle.
Sometimes it stays in the middle the whole day without any problem.

Whenever i accelrate the car, it immediately falls back into the blue zone.
The same symtom show with the AC on or off.

I have replaced the thermostat, fan clutch but don't know whats going on. looks like the thermostat is stuck open.
I have replaced 5 thermostats in the last five months but the problem is there. I have bled and rebled the system a lot of times.

Any idea what could be the problem or where to start looking

Thanks
Steve
90/525i

[Jazzman]

Have you tried checking your coolant temperature sensor? If you've replaced the thermostat that many times it could be the sensor.

[sbihue]

Have you tried checking your coolant temperature sensor? If you've replaced the thermostat that many times it could be the sensor.