Okay, just for ***** and giggles....what are the proper names of THESE sending units? The two on the back side of the thermostat/water pump housing? Top one has a green plug, bottom one is black.

 

Water Thermosensor and Thermoswitch.

 

So there are no fewer than FOUR sending units associated with the water level or temperature then? Because on the front is another temp sending unit plus the water level sensor, evidently......

 

one for the gauge, one for the ECU/ fan relay and one for coolant level and the 4th for been an Auto I guess.

 

The FC's had more sensors, believe it or not .

I think a lot of the reason is keeping some systems isolated and simpler. You could, in theory, use the main water temp sensor that feeds the ECU for everything, but you also put all your eggs in one basket - if that sender goes bad, you have backup sensors, in a way.

Dale

 

2 water thermosensors (one for ECU, one for dash gauge)
1 thermoswitch the turns the fans up one speed.
1 water lever sensor

 

which is the one that turns on the fans..the green one or the black one??

 

and for auto's, one more switch on t-stat hsg. I think it engages torque coverter lock-up more quickly if temps hit 230F+, to reduce heating trans fluid.

 

The black one on the bottom in the picture above (Thermoswitch).

 

Technically, they both do. The thermoswitch is routed directly to a fan relay, whereas the ECU thermosensor is routed to the ECU. When the ECU reads about 210F it turn the fans up one speed.

 

Thanks guys!

 

The stock ecu will turn fans on low based on the sensor, when coolant exiting the block hits 221F. The switch kicks fans up to med speed at 226F. If AC is on, fans start at low speed, and speeds will kick to med and high at those same temps.

Usual tricks to get lower 'on' temps near 210F are recommended.