temp gauge does not work - help!

[bmartin9122]

Can anyone give a novice here any ideas how to fix a non-functioning temp gauge on a '79 w/ a 350 v8? It does not even budge - however, the engine definitely gets warm. Thanks in advance.

[f.monroe]

First check the temp sending unit thats should be in the drivers side head I think . Make sure the green wire (?) is plugged into it tightly . If it is you should be able to check the gauge function by grounding the wire . The gauge should sweep to the right when grounded . If this is wrong , someone feel free to correct me . Frank

[DBLSPRT68]

I would try the sending unit also. It's on the driver side head just behind #1 spark plug. I think the parts stores carry them. There is a difference between factory guages and warning light sending units, so be sure the get the right one. Hope this helps. David

[bmartin9122]

Thanks guys. I will track it down and check this weekend.

[Slonaker]

Originally Posted by f.monroe

First check the temp sending unit thats should be in the drivers side head I think . Make sure the green wire (?) is plugged into it tightly . If it is you should be able to check the gauge function by grounding the wire . The gauge should sweep to the right when grounded . If this is wrong , someone feel free to correct me . Frank

That is all correct for my '86...

Slonaker

[bmartin9122]

I went in search of the coolant temp sending unit this past weekend. No luck! I found the oil pressure sending unit next to the dipstick tube. I did find an odd-looking component between the driver's-side front spark plug and the next one behind it. However, there was no wire attached, and I didn't see a bare electrical terminal on it or wire hanging loose nearby. I am hoping the manual I won on eBay helps.

[f.monroe]

Sounds like you found it . The head of it looks like a common nail head . The wire has an end on it that slips on it . If the end is missing , some people use a female blade connector . I am pretty sure the wire comes down the drivers side of the engine and runs along the valve cover . That is most likely why the gauge isnt showing anything . The thing that you found is the temperature sending unit . Frank

[bmartin9122]

Cool. I had a feeling I found it. You are right! The end looks like a nail head with a spark-plug-like base. I found a pair of green wires attached to the valve cover. One goes to some kind of electromagnetic plunger attached near the throttle. The other ends in a jagged stripped end with no connector! I put a voltmeter on the bare wire and got nothing with the key "on" and the engine running. I suspect this wire will show +12v when I turn on the A/C. Currently, the A/C compressor is disconnected because of a leak, and the connector is missing the +12v lead. I may be wrong - this has happened many times in my life.

[Slonaker]

That "electromagnetic plunger" is used the raise the idle when the A/C is running. It compensates for the extra drag the compressor puts on the engine. The wiring for it and the A/C compressor clutch wiring are both together in a loom that runs along the driver's side valve cover on my truck. I'm not sure, but they may both be green like the wire for the sending unit. I know for sure that the wire going to the sending unit and the one going to the clutch are green. If the two wires are together, they are probably the ones for the clutch and the "electromagnetic plunger" on the carb.

You will only have 12V to the wire for the A/C clutch if the system has a decent freon charge. If the system is empty, it has a pressure witch that prevents the clutch from engaging so that you don't burn up the compressor. If your A/C is discharged, you would have to bypass the pressure switch on the drier/accumulator to get the wire to read 12V with the ignition and A/C on.

The thing you found by the number 1 plug is definitely the sending unit. If you ground the wire going to the sending unit, assuming the gauge works, the gauge will peg out. I found this out when mine melted on the valve cover. It bounced on and off the valve cover as I went down the road, grounding every time it hit. The temp gauge bounced like it was possessed.

If I get a chance, I will try to trace the sending unit wire back to the firewall and see where it comes from. It might take a few days, though. PM me if you still need it and if I forget (I usually do ).

Slonaker