W204 C300 fan runs full speed at all times

[daveshea]

Hello!

I am a new owner of a 2010 C300 4Matic that I bought from an insurance auction - the car was a salvage car due to a front impact.

I have repaired all of the damage, but there is one issue that I cannot figure out.

Immediately upon starting the car, the radiator fan begins to run full speed, even though the car is stone cold. The AC is OFF. The radiator and condenser are BRAND NEW. This problem existed before and after the radiator was replaced.

The fan continues to run at its maxiumum speed, regardless of the engine temperature. I allowed the car to run today from cold to just above 80 deg. C before shutting it off today.

When one feels the upper radiator hose(driver side), it is HOT, and the air blowing near that side of the radiator appears to be hot.

The lower radiator (passenger side) is COLD, and the air blowing near that side of the radiator appears cool.

The heat is also turned on full blast, and blows lukewarm/cool air.

What is causing the fan to run full blast, and why is the coolant apparently not circulating?

My only guess is that the thermostat is stuck shut? Does that even make sense? Is there a sensor that is malfunctioning making the fan run full blast??

Please advise if able!
-David