Ok, there are a thousand threads on location of the sending unit and thermostat sensor. This is not my problem. I've got a 99 4.0 and from what I've read, there is only one cooling sensor on late models and its on the thermostat. No matter how cold or how long the car has sat, when you fire it up the temp jumps to 210. Just as if you popped in the post office for a minute and came back out. I've replaced the sensor and for kicks the thermostat, thinking surely this would resolve the problem, but it hasn't. I know that the temp will climb from there because I had a radiator leak and I overheated it once. When I replaced the sensor I unplugged it to see what type of reaction I would get and the gauge sank and threw the check engine light. After plugging it back in it still did the same routine. Anyone else have this same problem? Thanks ahead of time!

 

Never heard of that specific problem... You can test the sensor itself.


With the engine off probe the sensor and take the resistance reading.

Drive around to warm the engine to standard operating temperature.

With the engine off probe the sensor again and compare the readings.

It should be a lower resistance.... if not then you should replace the sensor.

 

Correct me if I'm wrong, but after doing so check those numbers vs what it reads at the back side of the gauge. if its getting a good signal to the gauge your gauge would be the problem. If the readings aren't the same you have a short, corrosion, or a ground in your wires!

 

The test is just to see if the sensor is okay. I don't know for sure but since there is only one sensor the wire will go to the computer first.

 

Oh true, so follow the wire to the computer, then follow the wire(s) from the gauge! Check your resistance threw the wires to eliminate them as the problem.