I know there are 2 coolant temp sensors, one behind the thermostat housing/filler neck, and one on the rear iron under the oil filter. So what exactly does each one do?

I have the one in the filler neck hooked up, and not the one in the rear iron. I get dashes on my PFC commander for water temp so I guess the commander and the stock gauge get their reading from that one. If I don't use that one, then I can't have my PFC monitoring water temps?

 

i believe the one on the water pump is the one that switches fans on, the other reads the temp, i could be wrong so lets hope somebody chimes in if i'm wrong.

 

there are two on the tstat housing. Top one is the temperature sensor, the bottom one with one wire coming out is the thermosensor, It tells the fans when to turn on and off. There is another wire that goes to the top of the Tstat that alerts you to the coolant level. There is a connection on the rear housing that is the coolant level disconnect.

 

There's actually 2 coolant temp sensors though. One is on the back of the filler neck along with the level sensor and fan thermosensor, and there is also one on the rear iron right under the oil filter.

 

Only one that gives a reading back to the PFC. That one is the Top sensor on the Tstat. The other on the front of the tstat, with just a wire coming out is the coolant level sensor.

 

You need all 4 connectors hooked up.

 

The sensor on the rear iron, under the oil filter, is connected to the water temp gauge on the dash. That's it's only purpose. You can confirm this with the temp gauge mod (which I did).