'68 SS Console temp gauge not working

[rags31]

 My temperature gauge is not working or barely registering on the cold side. It’s not worked since I got the car a couple months back. I had a small anti-freeze leak at the sending unit so at the same time I had the shop put a new sending unit in thanking the other was bad and I’m getting the same cold reading on my gauge.  I did some research on google and a couple searches I found tech threads that say when installing temp sending unit do not use teflon tape or any thread dope as the unit will not ground properly. Of course when the shop changed mine out they used thread dope but it wasn’t working prior so not sure if it was doped or not. I’m certain that we used the right part number for the gauge application and check grounded the wire and the gauge will fly to the hot side signaling it works.  I’ve bought another temp sending (ac delco) and plan on changing it out this weekend (after cleaning threads the head) but now I’m concerned about threading it in without anything on the threads preventing it from seeping anti-freeze again. 

Update: Changed out to new gauge (a/c delco G1852 #12334869) same as pulled out. Installed with no thread dressing ran motor up to temp (180) still gauge only will register one line above cold. Grounded temp unit wire and console gauge will fly all the way too hot side. Hooked wire bace to sensor and ran motor temp up to 190 and still no reading change. Had to pull sensor back out to teflon threads to keep from leaking. The only thing I know to do is change out temp gauge in console maybe gauge is bad but I can't figure out why when we test ground wire gauge registers!

Has anyone had this issue  - how difficult or easy is the gauge to change out?

thanks for any feedback. . .rags
 

[68Zproject]

Have your checked the back of the gauge for the resistor?  There are lots of threads on this issue when you do search.

http://www.camaros.org/forum/index.php?topic=3963.0

http://www.camaros.org/forum/index.php?topic=5425.0

[Mark]

Gauge normally reads 1 tick above 1/4 scale with the engine operating around 180 degrees, thats just how the originals work.

Heres some resistance values for three senders 6 dollar TU5 Wells sender from Autozone, 25 dollar "correctly calibrated" Lectric Limited model 01513321, and an original GM 1513321 sender (for a Pontiac Firebird - one with the slide on connector- Camaros use a 1513462 with a screw on lug).

80 degrees: Wells at 650 ohms, LL at 573 ohms, GM at 549
90 degrees: Wells at 526 ohms, LL at 445 ohms, GM at 524
100 degrees: Wells at 429 ohms, LL at 365 ohms, GM at 409
110 degrees: Wells at 328 ohms, LL at 266 ohms, GM at 365
120 degrees: Wells at 283 ohms, LL at 227 ohms, GM at 323
130 degrees: Wells at 250 ohms, LL at 200 ohms, GM at 272
140 degrees: Wells at 216 ohms, LL at 170 ohms, GM at 227
150 degrees: Wells at 198 ohms, LL at 155 ohms, GM at 195
160 degrees: Wells at 173 ohms, LL at 133 ohms, GM at 175
170 degrees: Wells at 157 ohms, LL at 119 ohms, GM at 157
180 degrees: Wells at 135 ohms, LL at 101 ohms, GM at 140
190 degrees: Wells at 120 ohms, LL at 89 ohms, GM at 125
200 degrees: Wells at 109 ohms, LL at 79 ohms, GM at 109
212 degrees: Wells at 104 ohms, LL at 75 ohms, GM at 102

If you have a gauge with an external resistor you can change it from the stock 86 ihm resistor to a 91 ohm resistor and that will move the gauge up to 1 tick below half, at 180 degrees. I've done that, I use a potentiometer with two short leads on it, I adjust it to what i want the gauge to read and then lock it down in a ball of electrical tape so it can't change. If your gauge has the resistor built into it, then you have to live with it reading low, or get a sender that has a lower resistance at each of the temps above.

[rags31]

Thanks for the replies. I've bought a new gauge (Classic Headquarters-GM Restoration) that has an external resistor. I'm not real technical but it seems changing out the gauge and resistor is straight forward bolt up. It you have any tips along the way I'd appreicate it.

thanks for the information

Randy
rags31   
 PS - It was mentioned using a different resistor might move the gauge closer to have way at 180 degrees - are they readily avaialble at auto parts stores? 

[69pace]

Are you sure the sender is correct one?
Bench test it.
You can remove it from the block, ground it with a test lead, and place in a pan of boiling water with a thermometer like you would test a coolant thermostat.
Then check its output with the gauge or multimeter.

It maybe an idiot light sender which I think if not mistaken only goes live at a particular temp, where a gauge sender sends a range out from cold to hot.

[rags31]

Good idea! After trying three different sending units and much searching I found upon a company that specializes in wiring and misc electirical components and they make temp sending units. The company is www.lectriclimited.com. They make claim that todays sending units from GM and after market are generic in nature i.e., designed to cover a wide range of applicatiions and are not very accurate.  Anyway they calibrate their sending units for vintage cars and for individual models. I purchased one of their gauges but haven't gotten around to  installing. I"ll post results as soon as I do.

Randy

i                 

[Mark]

Look at the post 3 above this one.  LL is lectric limited.  The lower the resistance for any given temperature, the higher the gauge will read.