Coolant Temp Gauge Not Working

[DavidB82]

Hello, I'm helping a friend fix their 2000 Explorer 4.0L OHV. The problem is that the temperature gauge sits below "C" whether or not the engine is warmed up. So, I searched around on this site and found the location of the Temp Sender (the sensor in near the thermostat with one 1 wire). I did the test of grounding the wire to see if the gauge works and it does. Straight to ground puts it pegged above "H" and putting a 100 ohm resistor in line puts the gauge somewhere in the middle.

So, I figured it must be the sender. I got a new one and put it in. Unfortunately, the needle still sits below "C". I let it warm up some to where the radiator hose was warm and the needle still hadn't moved.

I tested the resistance through the temp sender connector prong to the brass body and got about 2500 ohms. Given that 100 ohms put the needle in the middle I was wondering if the new temp sender might be bad? Does anyone have a chart/table of the resistance of the temp sender resistance vs temp?

If anyone has any other ideas I'm all ears.

Thanks,
David

 

[DavidB82]

Nobody??

 

[Kriegen]

how warm does the heater blow if you turn it all the way up? The issue could be a thermostat that is stuck open. My mountie had a similar problem, the temp gauge seldom went above C and my heater never blew more than slightly warm air. Replaced the thermostat and now the gauge goes to where it should and I get nice hot air.