The red topped sensor I am talking about is on the exhaust side of the block, just above and rearward of the Waterpump... I think it controls the electro-magnetic coupling for the engine driven fan on the 2.2D. The read cap snapped of the body of the sensor, and I think its toast. The temp gauge is working fine, and I think that sensor is in the head..
I will take a pic and post it in a few mins...

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2009 Mercedes ML320 Bluetec