Temp Gauge Intermittent

[Hubrick]

Hello 311s Folks,

This site and this forum sure is a great resource for a first time Fairlady owner. Hopefully someone out there has seen this problem and can point me toward a fix.

I've had this car for almost 3 months. From the beginning the temp gauge has been inop. Initially, I tried to ground the wire, and the gauge started to move up to about 120 F, then backed off and dropped back to zero. After testing the resistance of the sending unit, I put together a really good ground for the wire, and when well grounded, the gauge reads full scale at 250.

I talked to a guy on the list who said to rig up the ground bypass from the big nut on the sending unit to the stud where the thermostat mounts. Did that, and the same thing happened, temp gauge went up to about 120 and then dropped back to zero. In the last week, I've checked the resistance on the sender again - about 60 ohms cold and about 40 ohms hot, with the IR temp gun showing about 150 F at the thermostat. The contact says he doesn't think it's likely that its the sender, still thinks it's a ground problem.

So I was thinking wiring, instrument voltage stabilizer (regulator), or the gauge itself. The voltage at the inlet to the instrument voltage stabilizer is 12v, and with my digital meter, it changes rapidly between zero and some higher number pretty quickly and regularly, so I'm thinking it works. The fuel gauge seems to work well, although yesterday while driving, it seemed to drop from a little less than half full to nearly empty pretty quickly, and when I filled it up, I was only able to put about 6.5 gallons in it, so it might be a bit unreliable too.

I read on the 311s Tech Forum today about making sure the instrument voltage regulator is grounded properly - it was loose, so I took it off, wire wheeled the contact surface, scraped the mounting surface, and reattached it solidly. Thought I had fixed it, temp started to go up, and when the needle got to the 120 mark, it fell back off and stays at zero.

Sender is grounded, voltage regulator should be grounded, sender shows different resistance at different temperatures, gauge goes full hot when the wire is grounded, but no matter what I do - the gauge moves up to about 120 then falls back to zero - gee I've run out of ideas.

Can somebody figure this out and give me an idea what to do next ?

Thanks,

Rick Huber

[devo]

If both the temp gauge and the fuel gauge are having trouble, it could be the instrument voltage regulator. It steps the voltage from 12v down to 8v for those two instruments only. Here is a $6 fix for that:

http://www.311s.org/pmwiki-311/pmwiki.p ... VoltRegFix

[greydog]

Make sure the regolator is well grounded. On my 68, even with the screw tighr, iI sas an intermittent reading. I used a star washer to get a good ground.
Dan

[GeoffM]

The sending unit is cheap and readily available. I'd start by replacing it to rule out one variable.

[Hubrick]

Thanks guys, I'll give those ideas a try.
Cheers,
Rick

[Hubrick]

Changed the sending unit today. Pretty disappointing - symptoms are exactly the same now as they have been. Two weeks later $41 poorer, and back to square one. Temperature comes up to about the middle of the 120 range, then drops back off to zero. Ground the wire, and it goes up to 250. Seems to me it has to be the voltage regulator, but then the fuel gauge reads something, although it sure does move around a lot. Guess I'll check the ground on it tomorrow.

[Gregs672000]

It's the regulator!

[Hubrick]

Yes, must be the regulator, but with the gas gauge working almost normally, that has kept me from targeting it. Think I'll read about the $6 fix on here again instead of ordering the $168 new one.

[mraitch]

I'm having the reverse problem - temp works fine - gauge pegs at full regardless - at least it is now 'workng'.

I have checked the resistance on the gauge, shifts when move the float arm. Always thought 'essentially' that if either worked, the issue would be external with theone that didn't.

Like all for two and two for all!