Engine/Transmission (1994 - 1998) Water temp sending unit not right?

[Deezul1]

I thought my thermostat wasnt closing at all and installed a new Cummins unit and still dont get temps over 150 degrees but can watch the gauge cycle from barely on the gauge to 150 or so which leads me to believe the stat is working and the gauge is wrong. My infra red thermometer showed outside block temp to be about 165 deg measured under the intake manifold behind the inj pump and it was 45 deg outside temp. Any ideas? how to check the sending unit?

TIA

John

 

[Deezul1]

No ideas out there?

 

[dslmacdown]

Try this: with the key on, disconnect the sending unit wire and ground it. Does the temp gauge peg out hot? If it does I would change the sending unit. If not check the gauge itself and related wiring. I would bet the sending unit is bad.



MAC

 

[15w40]

The coolant sensor is a thermistor. It changes its resistance as the temperature of the coolant changes. Unlike most sensors its resistance is inversely proportional to temperature which drops its resistance with a rising temperature.



Here is the specification:



0*C, 32*F = 30K to 36K ohm

25*C, 77*F = 9K to 11K ohm

50*C, 122*F = 3K to 4K ohm

75*C, 167*F = 1350 to 1500 ohm

100*C, 212*F = 600 to 675 ohm



Hope this helps.





Oops, I just noticed this thread was mover to the 12-valve section. If I had read you had a ‘97 I would not have posted about the ISB 24-valve temperature sender. Sorry.

 

[Deezul1]

Thanks guys, thats what I needed, some ideas to get started on.

 

[MMiller]

I posted here a few weeks ago about my brothers trucks and have failed to update. My brothers gauge worked fine, but the guage started not reading any temp. He installed a new thermistat, and the top radiator hose was getting warm. We never checked ohms of resistance of the sender. He had the wire on and off several different times, grounding it, checking the gauge. The gauge and wire tested fine.



I did have him loosen the sender and then tighten it back up. For some reason since he has done this the temp gauge has worked perfectly since then. Oh shucks now I just jinxed it, I am now awaiting his phone call saying the gauge is not working again . I kinda think that the ground was not good between the sender and the block, I know its a long shot, but how else would you explain it. I would loosen the sender and tighten it, just for s&g's before buying a new sender, can't remember how much a new one was, but I think cummins was cheaper then dodge, and they didn't have any available.





His truck is a 94 2500 4X4 CTD for your info. Hope this helps.



Michael

 

[TJMoor]

I had a simalar prob. last summer and replaced the sender. . Then Just two weeks ago it did it again, this time I took it out cleaned off the teflon I had used to install it , put it back in , and it has worked fine since... .

just my 2. 3 cents

Terry