Temperature sending unit

[triton28]

Behind the RH cowling in the area of the radio amplifier/cruise actuator is where the Yellow/White short wire from the coolant temperature sensor connects into a Yellow/White wire stub from the main harness. Perhaps this bullet connection is corroded/separated.
Also there is a test for the coolant temperature sending unit on page 15-36 of the repair manual.

[robgest]

I will check the wires and ground it when I get home. If the gauge doesn't move when grounded should I consider checking the gauge?

[chevyman1]

I would check the wire make sure it is not broken somewhere.

[triton28]

If you are sure of the grounding of the thermostat housing and you find the Yellow/White wire is making good connection with the main harness stub with the bullet connector, then I would check the Y/W wire between the bullet connection and the white plastic connector block which goes into the gauge cluster for continuity. A multi meter set to Ohms will confirm/deny the continuity of this wire. If you have continuity then the gauge is suspect, or less likely, the wire is bad between the plastic connector I spoke of and the gauge itself.
Don't forget that there was a time when the brass female end of the wire coming from the brass male tip of the sensor itself was giving owners problems because of being loose/corroded at the tip of the sensor. The solution was cleaning of this connection and making sure the brass connection was tight fitting onto the tip of the sensor.

[usmalenurse]

If you are sure of the grounding of the thermostat housing and you find the Yellow/White wire is making good connection with the main harness stub with the bullet connector, then I would check the Y/W wire between the bullet connection and the white plastic connector block which goes into the gauge cluster for continuity. A multi meter set to Ohms will confirm/deny the continuity of this wire. If you have continuity then the gauge is suspect, or less likely, the wire is bad between the plastic connector I spoke of and the gauge itself.
Don't forget that there was a time when the brass female end of the wire coming from the brass male tip of the sensor itself was giving owners problems because of being loose/corroded at the tip of the sensor. The solution was cleaning of this connection and making sure the brass connection was tight fitting onto the tip of the sensor.

Reviving this old post as I am trying to figure out why my temp gauge is not working now. I was worried that it might be overheating but after making sure the fan was working correctly, I don't think that is an issue. Thought I'd try to figure out this "grounding" to see if it would work. The thermostat is not grounded as far as I can tell. Only wire I see coming from the thermostat is the wire coming out of the temp sensor wire underneath the thermostat. Question about this....does that wire just pull off from the temp sensor? Is that the "female end" you're speaking of? I have a long hemostat but don't want to pull on wires that are not supposed to disconnect...especially wires that are not easily accessible! The "bullet connector" looks like it has been tampered with before by PO as there is some electrical tape on the engine side of the wire going into the connector but the wire looks intact? Thinking about just cutting the connector out and adding a new connector to make sure. Still a little confused about the "grounding" part as well. Do you just add a ground wire anywhere on the thermostat housing and then to the frame or is there a specific location to add the ground wire? I have read and re-read the posts but after getting all the hardware and battery out of the way, I am still not sure.....any help is appreciated.

[triton28]

Yes that Y/W wire ends with a female bullet connector which fits directly onto the end of the temperature sending unit.
Actually I am of the opinion that the thermostat housing is in fact grounded by virtue of the steel mounting bracket being bolted to the frame. This belief however relies on perfect metal surface conditions on both the aluminium t'stat housing and the steel bracket where they meet. Generally over time dis-similar metal electrolysis causes a corrosion to build up at the point of contact and then the t'stat housing will start to exhibit poor, or in some cases, no ground characteristics.
The easy solution is to introduce a dedicated ground wire from under the head of one of the t'stat cover bolts, #s 132j0620 on the water pump illustration, to a nearby frame bolt.
Dave

[ekap1200]

I will check the wires and ground it when I get home. If the gauge doesn't move when grounded should I consider checking the gauge?

Don't HOLD the gauge lead to ground , rather just tap and look for a deflection. grounding the lead and holding will bury the needle and at worst damage its windings.
If you take a jumper to the neg side of the ( removed battery ) and connect to the chassis, then a test lamp from B+ to the thermostat housing . The lamp will light if the thermostat housing has a good negative ground.
The oem neg battery cable is where the wire comes from , that grounds the thermostat. The thermostat is bolted to the frame but they added a neg cable from the batt to it also.

[usmalenurse]

Did the ground wire and got everything back together yesterday. Temperature gauge working like a charm now....Thanks for the help...