My temp gauge is not working correctly and I'm wondering if it is my gauge or my sending unit. The needle on the gauge never goes below 12 o'clock position (200 degrees?), even after sitting for several days with the car off. When I turn the key on it moves immediately over to the 1 o'clock position (240-ish degrees?). What position should the needle be with the key turned off? Should it still be 12 o'clock temp or does it go all the way to the left? If it is supposed to go all the way left would that mean that my gauge is the culprit? And if it is supposed to be at 12 o'clock with key off would that likely mean that the temp sender is the culprit?

I have a new temp sensor on the way since they are only $20, but would like to hear thoughts before I go through the pain of replacing that as it is up under the exhaust manifolds with AIR system. Thanks!

 

Responses will improve immensely if you tell us what year model we're working with.

 

It is a 1980.

 

Remove sending unit wire from the sender. With it not touching anything, turn ignition to ON (engine OFF). Gauge should go to full-scale RIGHT. Now touch that wire to an electrical ground (metal on engine block, negative lug on alternator, radiator support) and the needle should go to ZERO. If those two tests are successful, replace the sending unit. If you get significant change between those tests, but not full scale LEFT & RIGHT, the problem could be with the sending unit or it could be with components mounted to the gauge or it could be a combination of both things. If you can repeat any of these tests and get the same readings on the gauge, your problem is most likely NOT the gauge and NOT the wiring.

 

Thanks 7T1. Is the gauge needle supposed to be at 12 o'clock with key out of ignition?

Edit: I just did the test and unplugged it moves a little to 1 o'clock position and when it is grounded (to negative battery post) it moves right just slightly, not full right. Either way it failed. I guess I'll get a new gauge and try so see if that fixes.

 

Since your gauge moves it could be that the 90 ohm resistor on the back of the gauge is bad/open.
Might want to pull the gauge and test the wire wound resistor before throwing money at the gauge.

 

If you read my post again, I stated that "if the gauge moves at all" the problem is NOT the gauge. With ignition OFF, the needle on the temp gauge can be anywhere.

I tend to agree with the above post that the calibrated wire-wound resistor on the rear of the gauge could be 'defective' in some regard. The sender could also be in error, but you won't know that until you assess and correct the resistor issue. If your testing was without the sender connected to the circuit (as I described above), the sender ALONE cannot be all of the problem.

I suspect the gauge is NOT defective. A defective...but working...gauge is very unusual, but it could happen. I certainly would not spend money on a new gauge until you opened up the gauge bezel and checked things out completely.

P.S. You shouldn't substitute a 'common' resistor for the wire-wound part attached to the rear of the temp gauge.

 

If it is the resistor the only option I have seen is to buy a new gauge, or get the programable resistor from Wilcox. Is there a source for the resistors?

 

Check your sending unit, I have seen where somebody installed the wrong sending unit, if you have an "ON/OFF" sending unit for the dash warning light hooked up to a "gauge" it just won't work.

I saw a car once that the sending units were installed reversed like this and did the exact same thing. It is worth checking as is the grounding of the engine and instruments as well.
Good Luck!

 

I think he could use a 90 ohm 5w resistor - there's a thread on that somewhere on here.

 

I thought that either Willcox or Lectric Limited sold the wire-wound resistors.

 

If you're going to go in there anyway, then just order the Willcox adjustable resistor for your 1980. Either way you'll be better off and be able to dial the gauge in as well as it can be done. I wish I would have done mine as soon as they came out since it works so well.

 

Yup, good call there. I checked mine and have the unit for a gauge, not light.

 

Might help

 

Soon...

We will have replacement resistors for all the 1965-1976 cars and the 1977-1982 cars in a week or so. We thought we had them ready to go and the people that made the boards goofed them... It's funny because when we design the Gerber files for the boards and send them in...there wasn't any issue.... but sometimes we have to add an extra hole so that they will drill through all holes (just like our tach boards and the delay timer boards). When we left the hole off, they didn't drill through all the holes and so the boards have continuity on both sides and they are were not supposed to be this way... The boards we received will work for the 77-82 cars but not for the 1965-1976 cars.. it's complicated...

Funny thing is this is the same reason the imported tach boards need washers.... they're plated through and running a small drill through the holes would solve the issue (aside from their cap bleeding off)... It's even more funny because this is why we made our USA tach boards....

We tried to tell them what they were doing wrong, and we were contacted by their supplier... We told them about the cap issue... and what we were doing to fix the bleeed off issue... and they got pissed at us and was told to not contact their import supplier again... go figure.... Even though their supplier purchased a calibration machine from us to see if he could figure out the issue.

I believe the idiots name was Chris Fink..... He pissed me off so bad that I figured it was cheaper for me to make the board than to continue fixing theirs... so I did...

So right now we are waiting for new boards and then we'll stuff them as quickly as possible.

Here are the links for the resistors, but please know that they will be about 1 week from being completed... maybe longer.

We have the pcb's made in California and sometimes they are a bit slow getting them to us. The resistor posted below is from our proto...

You can view all the options at this link... https://willcoxcorvette.com/catalogs...ar=&q=resistor

If the OP is working on a temp gauge and you want to dial it in then use the adjustable resistor. It's really the best option and the adjustable resistor will work for other gauges but it's set at 90 ohms... so if used on a 1977-1982 car on another gauge it would need to be dialed in according to the color of the existing resistor assuming it's being used on another gauge other than a temp gauge. On 1977-1982 cars (other gauges aside from temp gauge), the resistance is determined by color of the existing ceramic resistor.

https://willcoxcorvette.com/catalogs...=adjustable+re

 

I have the adjustable resistor from Willcox in my '79 and I can't imagine why anyone would spend money on the regular resistor. The adjustable part is absolute genius. My temp gauge is accurate for the first time in the life of the car.

 

Why do anything else? It's fantastic.

 

Yes it is... it'll work for other cars too not just Corvettes... but I have no idea about other cars so I've not pursued it. It'll work on any manual temperature gauge and because it's pre-set to 90 ohms it'll work as a replacement resistor for any of the other gauges that used a wire wound resistor. (Or for that matter, on the 77-82 cars it can replace any resistor in the center cluster).

To be honest, it was ROGER that pushed me to do the adjustable resistor. (not on the forum any longer, and while we still talk he's retired in the sunshine state). Without his urging, I doubt I would have pursued this part...

So accolades go to him (give credit where due). He knew that I had a bit of an electronic background and I walked him through this years ago on a car he was working on. It worked and then he began bugging me to make the thing for everyone so I did.

Ernie

 

"Not to hijack the post"....but that is what you're doing.

Just start a new thread on your topic.

 

Done. But if you didn't know the answer you could have just said so.