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temperature gauge sending unit

fjord

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1999 Explorer 4.0 V6 OHV
My temperature gauge is not working so yesterday I replaced a temperature sending unit located out by the thermostat housing. Of course this did not start the gauge working. So I searched the forum some more last night and found out there are two different coolant temperature sending units on the 4.0 V-6. There is another sending unit directly in front of the coil pack (right by the fuel pressure schrader valve). I am wondering if this is the coolant temperature sending unit for the gauge?
 


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budwich

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the one for the gage only has one wire connected to it while the "engine controls" one has two. IF you ground the single wire, your gage should go to high otherwise you likely have a wiring issue and not a sensor issue.
 




fjord

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Ok, thanks budwich. The sensor that I changed out (the one at the front of the engine-by the thermostat housing) did have the one wire. I verified that it is the one that controls the gauge by grounding out the wire in the connector like you suggested and it did indeed send the gauge all the way to the top. However, with the connector connected it still just barely moves the gauge even after the engine has been running on a trip of thirty minutes or so. I checked the resistance in the sensor between the two poles and at full cold and it was basically open (no resistance.. only 2 or 3 milli-ohms?...anyway..had the multimeter set to 2000) At full hot (after running engine for 30 minutes or so) the resistance checked out at about 310. I am wondering if the new sensor is defective?
 




budwich

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if you search, you will find a conversion table that will give you an approx. value for that resistance. Go from there.

PS. quick look appear to indicate somewhere around 170 maybe. Sounds cool, perhaps the wrong thermostat or stuck ajar. Best way to confirm is either with a hand held or a odb data "grab" of what the engine controls are reading from the engine.
 




koda2000

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170 degrees is fairly cold. could be why your gauge hardly moves. the middle of the gauge's range should be about 195-200 degrees. thermostat is suspect or possibly the sender doesn't have a good ground.
 




Lefty2053

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This is strange. I just had a shop change the 1 wire sensor and it didn't fix my gauge. I just replaced the 2 wire sensor this morning and now the temp gauge works fine. I read there is one book that says it is the 2 wire and another book that says it is the 1 wire sensor. Mine is a 5.0 though.
 




koda2000

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This is strange. I just had a shop change the 1 wire sensor and it didn't fix my gauge. I just replaced the 2 wire sensor this morning and now the temp gauge works fine. I read there is one book that says it is the 2 wire and another book that says it is the 1 wire sensor. Mine is a 5.0 though.

that is strange. technically the one that runs the gauge is a SENDER, which only needs one wire. the other is the coolant temp SENSOR and it has two wires and it talks to the PCM. did you actually see the two parts replaced? the sender has a cylindrical shape on the business end where the sensor end is larger in diameter and has a conical shape. well, as long as the problem's solved.
 




Lefty2053

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I know for sure the gauge didn't work after replacing the 1 wire unit which is to the right of the coil packs. I replaced the 2 wire sensor which is under the coil packs and the gauge now works. I saw the 1 wire sensor was replaced as it is new and physically replaced the other myself.
 




budwich

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as they say.... whatever works, works. As posted, the "test" is grounding the wire and seeing what the result is. That should tell which sensor that you are playing with.
 




fjord

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1999 Explorer 4.0 V6 OHV
Haven't had a chance to research the problem any further yet, but I do know that when I grounded the "one wire" sensor connector (on the front of the engine by the thermostat on my 4.0 V-6) the temp gauge maxed out. And when I took the ground wire off, the gauge went back to zero.
 




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