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Re: Zeroing temp gauge to sender
#88871 Tue Oct 16 2007 01:06 PM
Joined: Nov 2000
Posts: 582
4
Shop Shark
I'm working on that aspect right now. Been measuring ohms at different temps and testing gauge reading. I have an original AC temp gauge with a 100-212 degree range and there is no spot on it to do any tweaking or zeroing of the gauge itself. The only spot where the needle can be altered is to bend the brass tab a bit. I have some ohm reading on another recent post in this section of the forums.


Country Roads, West (By God) Virginia
http://community.webshots.com/user/geezer
Re: Zeroing temp gauge to sender
#88872 Tue Oct 16 2007 02:10 PM
Joined: Nov 2001
Posts: 128
F
Wrench Fetcher
Hi Geezer,
Thanks for the reply. Where is the other POST. I did a search uner ohm's, but did not come up with any results. This may be a good link for others going throught he same difficulties.

Re: Zeroing temp gauge to sender
#88873 Tue Oct 16 2007 05:08 PM
Joined: Nov 2001
Posts: 128
F
Wrench Fetcher
I believe I found the POST that you were referring to, but it does not have a conclusion on results. If I am wrong, please advise. I really could use the high and low limit values for my gage (45 gmc 1/2 ton) to spec out the right sending unit. THanks again!!

Re: Zeroing temp gauge to sender
#88874 Tue Oct 16 2007 08:55 PM
Joined: Nov 2000
Posts: 582
4
Shop Shark
Here's a link to the other post. No, don't have resistance values as yet. What I am pursuing is finding the original GMC gauge (either part number or unit) and an original sender(same). Then if I am successful, I can measure the ohm readings at at least three different temperatures. Then I could post them so others could measure the senders they have to see if they are within a reasonable range to work with the gauge. The best scenario would to be to identify a current part number of a sensor and people could buy that. Will keep on working at it.


http://www.stovebolt.com/bboard/cgi-bin//ultimatebb.cgi?ubb=get_topic;f=3;t=002882


Country Roads, West (By God) Virginia
http://community.webshots.com/user/geezer
Re: Zeroing temp gauge to sender
#88875 Wed Oct 17 2007 12:18 PM
Joined: Nov 2001
Posts: 128
F
Wrench Fetcher
Thanks Geezer. Here’s an update on my end. I pulled my gage from the instrument cluster to get access. I first kept the two wire connection “as is” on the back of the gage with no results. I then switch the hot and sender wires on the back of the gage. The gage was hanging sideways from the wires below the instrument cluster, and as a result, the needle was showing in the middle of the range with no power. The needle seems to move freely, depending on how the gage is rotated and has a tendency to be in a 9 o’clock position naturally so as you rotate the actual gage around physically, the needle again will show a horizontal position. I pulled the sender from the motor. Once power was turned on, and a simulated grounding to the sender with the sendor wire connected from the gage to the sendor, the needle moved to the right. When I up righted the gage to it’s normal viewing position, the needle was pegged to the left, almost like the entire gage is mis-aligned, or the resistance is too high?

I purchased a few resistors. #1 measures 10 ohms, #2 measures 119 ohms and a third #3 reistor measures .295 K ohms. Now, I tried to put the three resistors in line one by one to see the effect. I pigtailed the resistor to the lead on the sender. Then connected the sender wire from the gage to the resistor. I tried all three above, and #1 did not change the overall needle movement from the “un-resistored” sender. #2 changed the needle movement to ½ the previous movement (meaning the needle moved 1/8” vs. 1/4"”) and the #3 changed the needle even less. What does that mean??

So, I believe the gage is working, and the sender is working, it’s just the resistance must be so high to start that it does not even register.


One more note, I did heat up some water, dropped the sender in, and the checked it against a cold sender installed. There was a larger needle movement on the heated sender than the cold (meaning, the needle moved another 1/16 -1/8” ). Makes sense, but the needle movement was in my opinion slight. Meaning, the needle only moved about a ¼” at its tip while just the sender was installed (again, while the gage was on its side allowing the needle to start off in the gage range of view.)

Any thoughts on where I am, and what I should do next?

Re: Zeroing temp gauge to sender
#88876 Wed Oct 17 2007 12:35 PM
Joined: Nov 2000
Posts: 582
4
Shop Shark
I also tried various resistors in line with the sensor with either no additional movement or a total peg to the hot position. Don't think that is the way to go. I've got a couple of inquiries in to some NOS parts suppliers on a gauge and sender. Waiting for a response from them. By the way, the needle on the NOS Chevy gauge that I have also reacts the same way as you turn it around. Moves freely between 100 and 212 degrees. So your gauge is probably fine.


Country Roads, West (By God) Virginia
http://community.webshots.com/user/geezer
Re: Zeroing temp gauge to sender
#88877 Wed Oct 17 2007 09:44 PM
Joined: Nov 2000
Posts: 582
4
Shop Shark
It's interesting I guess that I do temperature control systems as a living. I decided to call up one of my sensor suppliers who I purchase NTC thermistors from all the time. I posed the question: "If you have a thermistor of a given range and you apply 6 VDC to it or 12 VDC to it, what will be the measured result?" He said, UM........
However, he stated that thermistors are rated in applied voltages and are self-heating at those voltages. The ones we use in our business are 0-5 VDC as applied to the temperature measuring circuit. This would translate closely to 0-6 VDC in the truck. He also stated that if you apply 12 VDC to the same circuit, the thermistor would then tend to overheat, causing its internal resistance to fall which would translate to a higher reading on the gauge itself. I do believe that this may be what is happening in my case. I am applying 12 VDC to the original sender circuit and the gauge is reading 135 degrees when the actual temperature is 180 degrees or so. Therefore, I think that a 12 to 6 VDC voltage reducer is needed in the circuit to the gauge. This might possibly change the final reading and make it more correct. I'll experiment with this next.


Country Roads, West (By God) Virginia
http://community.webshots.com/user/geezer
Re: Zeroing temp gauge to sender
#88878 Wed Oct 17 2007 11:27 PM
Joined: Nov 2001
Posts: 128
F
Wrench Fetcher
Geezer,
I have a in line 12 to 6 Voltage reducer currently. If what your saying is true, this would not help my situation any. I am trying to get my truck ont he road for the first time, but need to have confidence that the motor is ok. I actually have a show on Saturday, so my time is limited. I wish I could come up with a ttemporary fix for now. Keep me posted as I will do the same.

Re: Zeroing temp gauge to sender
#88879 Fri Oct 19 2007 08:09 PM
Joined: Nov 2000
Posts: 582
4
Shop Shark
Set up a test station on my workbench today. Used a battery charger that delivers either 6V or 12V. Ran the hot to one side of the 100-212 NOS gauge I have, then left the other side of the gauge to the center terminal of the sensor and clamped the negative of the charger on the sensor threads to complete the circuit. Put the sensor in a shallow pan of water and heated the water from underneath. Tried a TS-6 sensor first (which is what you get from the repops). No reading on the gauge until it got to about 195 degrees at the sensor (I used a thermometer to measure the water temp) and then the gauge spiked to 212 degrees. Let it cool down and the gauge moved a bit downward then dropped totally to the other end of the scale. Kinda shows what others have said their experience is with the senders in their trucks. Tried three other sensors and pretty much the same deal. Then switched the voltage to 6v and repeated the process. On 6v power, none of the sensors registed on the gauge no matter how hot it got. I looked at three of the sensors and they are marked 12v. I'm thinking that I'll purchase a 6v sensor (if I can find one) and try that to see how it reacts. If my guru at the factory is correct, a 12v thermistor is calibrated to be accurate at 12v. Therefore, a 6v thermistor should be done the same way. I scored a NOS GMC 100-220 temp gauge yesterday so once I get it, I'll test it as well.


Country Roads, West (By God) Virginia
http://community.webshots.com/user/geezer
Re: Zeroing temp gauge to sender
oldblue #330299 Tue Oct 30 2007 02:19 AM
Joined: Nov 2001
Posts: 128
F
Wrench Fetcher
Hey Geezer and TOny,
Any updates? I was wondering if there a company that can take the gage and sender and calibrate?

I seem to remember that there are some nuts on the back of the gage, that are inked with paint shut. I wonder if these are the adjusting screws referred to on this post??


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