Coolant temp sensor?

Hi everyboby, I have a 1997 Disco 2.5 300 TDI. I have just taken the head off because the gasket blew and its being skimmed. I noticed a sensor screwed into the top of the cylinder head near the manifold which I think is the coolant temperature sensor. Can anyone tell me what happens when it senses high temp. Also there were two pipes bolted to the rear of the cylinder head I think these are transmission breather pipes but I cant see where they go to in the engine compartment. The ends of these thin plastic pipes have melted. Should it be one pipe forming a loop or is something missing. Hope someone can help. Thanks. Brinks

That sensor is for the EGR ECU. You probably always want it to read cold as that would stop the EGR from working. I would not even bother with it to be honest - the important one is the one screwed into the stat housing.

The pipes: if they disappear down to the transmission then they are the breathers, has the melted plastic blocked them? If so, cut the ends off to create new open ends.

Thanks discomania for the quick response, I will cut off the melted part as you suggest.
I couldnt see where they were going to but if they just breath, no problem. I will ignore the sensor as you say as the EGR has already been blocked off. Thanks again. Brinks