Thread: 300TDI thermostat housing

Neither. The temp gauge sender is nestled down on the other aluminum bit, the square looking adapter that connects to the head. It is a small ordinary looking 1 wire connecter, whilst those two big two wire senders are for the AC. One disengages the AC if the coolant gets too hot, and the other activates the AC fans if the coolant gets hotter. If you've been working the engine hard, and after you turn the engine off you notice fans coming on, that's what it is. ( Engine heat soak tends to occur more in v8's. but that's the rough idea)