factory temp gauge troubleshoot help

[firekiller15]

First of all, I did a search on this topic and came up w/ nothing substantial. How do you troubleshoot a temp sending unit? I have refurbished factory gauges, they all function except for the temp gauge. Radiator has plenty of fluid, my radiator cap has a built-in gauge that reads 155 degrees at idle but, no reading on the dash gauge. Tested the gauge w/ a 9v battery and seemed to function fine. Any suggestions? '72 Sport/ 302. Thanks.

 

[Viperwolf1]

Ground the sender wire. The gauge should go to full scale. If it does you have a bad, wrong or ungrounded sender. If it doesn't, something is wrong with the wire between the gauge and sender.

 

[firekiller15]

I grounded the sender wire (red/white wire) and my gauge does move but, only to the 170 degree mark. I will replace the sender and see what happens. If that is'nt the problemand continuity of the sender wire is good, how should I ground the sender? thanks.

 

[Bronconaut]

I had a similar problem. Mine would read "correct" when you first turned the key on but would then slowly move down to zero over the next few seconds.

Everything checked out. I could ground the wire at the sender and it would peg. I replaced the wire from gauge to the sender, then from IVR (instrument voltage regulator) to gauge, new sender - all the same. All the other gauges worked fine. I happened to have replaced the IVR before I started troubleshooting this. I had also replaced the ammeter with a voltmeter so I connected the IVR output to the voltmeter so I could see the pulse. I was only getting one pulse every 2-3 seconds. I've read on here and elsewhere that it should have been 2 per second. Rather than spending another $50 or so on a new IVR, I found several schematics and built a digital one using Radio Shack parts. I was then able to adjust the voltage output so the temp gauge "works" - I need to verify temp, oil pressure, etc. now for accuracy but for right now I know what the "ranges" are for normal on each gauge. I was able to adjust the output using the potentiometer from 2-7 volts. Right now I'm having to run it almost at 7 for the temp gauge to work.

Here is the result of my Radio Shack build - I'll get pics of the unit I made later - it's under the dash ;-)

 

[firekiller15]

I replaced the factory IVR w/ a solid state one from westcoast broncos already.

 

[firekiller15]

I replaced the temp switch, it now works...thanks guys. 20 problems down and 10 to go!

 

[Viperwolf1]

I grounded the sender wire (red/white wire) and my gauge does move but, only to the 170 degree mark. I will replace the sender and see what happens. If that is'nt the problemand continuity of the sender wire is good, how should I ground the sender? thanks.

The sender is fine. You have high resistance in the wire.

 

[DirtDonk]

Yeah, even though you say it's working now with the new sender, I would still verify that the wire is good. Your first test clearly showed that you were either not getting a good signal through the wire, you weren't on a good enough ground, you didn't leave it connected long enough, or your connection to that ground was too tentative.
Gauge should have pegged (buried the needle so to speak) when you grounded the wire with the key on.

Presumably though, you've run it sufficiently to say that it can go above 170 with the current setup? If so, you may still have a bum connection somewhere.
But at least it's working well enough now to allow you to move on to number 21.
For awhile anyway!

Paul

 

[firekiller15]

I'll check the wire and harness connections between the sender and gauge for corrosion.

 

[oleguy74]

take the teflon tape off.