Please help...this time it's the temp gauge, 68 Z28

[barsteel]

Hello!

A few weeks ago, I was able to get my fuel gauge working with the help of some comments and pics from other users here.

Thank you.

Now I'm trying to get my temp gauge to work.  I found out the hard way that the fuel gauge was not working because the wiring was incorrect, so that may be the case for the temp gauge as well.  I've attached a pic, and I hope that someone can set me straight if the wiring is incorrect.

NOTE:  I've since added a ground to the bottom terminal of the gauge, as it appears that it should have a ground based on the pics I was able to find.  If the gauge is not grounded, it pegs full hot.

Here's what I've got...

Gauge is brand new from Rick's Camaros.

Their website states that the gauge is NOT internally resisted, so I need a shunt resistor, which I ordered from them and installed as well, as shown.

The sending unit is well grounded in the block.  Resistance between the brass body and the block is +/- 1 ohm.

The resistance for the sending unit itself is about 750 when cold.  I warmed the engine up somewhat and now it's reading about 160.  From what I understand, that range is correct for a factory sending unit, please correct me if I'm wrong.

Rick's website says that the gauge is rated for between 55 and 225 ohms(??!!!) - a range that does NOT match the sending unit ohms. 

With the gauge hooked up as shown, with the ground, the gauge will only go to less than 1/8 warm when I run the car for 15 minutes or so, which should be fully warmed up, or very close to it.

Can someone please:

1)  confirm that I have the gauge wired correctly
2) confirm the resistance range for the factory sending unit
3) Let me know if I'm missing something

Thanks...

Chris

[barsteel]

I did some reading and found a table for "typical" resistance for older GM sending units on a Corvette website.  It seems that at room temp, most of the sending units show between 570 and 650 ohms, and around 80 to 95 ohms at 212 degrees.

Going from memory, my sending unit put out about 750 - 800 ohms at room temp.  I just pulled it out and took it for a spin to get it up to full operating temp (which involved getting on it a few times...the sacrifices we make!), and put the ohm meter on the sending unit.  With the engine full hot, I got about 170 - 180 ohms resistance, which is far above what is listed as "typical" for the lowest resistance.

Based on the listed typical resistance values for the sending unit of 80 - 570, and for 55 - 225 ohms, the gauge should start registering around 130 degrees, and show half hot around 180 degrees.  Here's a link to the page with the resistance values.


http://www.lbfun.com/warehouse/tech_info/gauges%20&%20instruments/Temp-Sending-Unit-and-GaugeCF-Thread.pdf

It's looking more and more like I have a "going bad but not totally shot" sending unit.

Agree?  Disagree?

Chris

PS - ran a permanent ground to the temp gauge, and now it falls to full cold with the power off, and pegs at full hot when I ground the sending unit wire, so the gauge appears to be working fine.

[Daytona Yellow 69 Z/28]

I had a heck of a time with the temp gauge in my 68 SSRS but finally got it worked out & working. After 3 different sending units. I finally had to remove the stock resistor from behind the gauge and swap it to a potentiometer set @ 129 ohms to get the result I was looking for. There was a thread on TC that really helped & I want to give another big thanks to Mark C & the other guys as they set me on the right path to get mine worked out & woking the way I wanted it to.

You might start at the beginning of this thread as there is a bunch of great info through out it. I was expecting to only need 91 ohms so I ordered a 100 ohm potentiometer & had to add another 50 ohm in series but a 150 ohm potentiometer would have been perfect.

http://www.camaros.net/forums/showthread.php?p=3121513#post3121513

I hope this helps & good luck..
Nick.... Rarerat on TC

[69pace]

Chris - I take back what I was going to say your picture is not left to right. so it looks correct.
Do you have resistance across the resistor?
Do you have any ohms from the sender in the block 0 is cold

Brian

[barsteel]

Brian -

I did check the resistance from the sensor body to the block, and I got +/- 1 ohm, which I don't think would really throw anything off noticeably.

I have a new sending unit on order from Ricks.  I'll let everyone know what happens when I install it.

Chris