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Discussion Starter #1
Hi,
I just finished my restoration on my 70 chevelle. My question is how accurate is the factory temp gauge. I can run my car all day and the gauge does not go much past the first line past 100. Any possibilities? thanks
 

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Mike

You should be concerned something’s not right. What thermostat are you using? Even with no thermostat it should get hotter than that. Did you run the car with the temp gauge before the resto and was it working correctly then? Did you change anything on the gauge or the sensor? You may have the wrong sensor, the wrong resistor on the gauge back, the resistor not installed correct or maybe a bad gauge to circuit card connection.

As far as the accuracy. in my experience I would say plus or minus 5% would be typical.
 

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Discussion Starter #3
I did change my dash from idiot lights to full gauge package. had the gauge package all redone and gauges callibrated. all new wiring harnesses. I did notice on the back of the temp gauge there are 4 terminals two are hooked to the printed circuit board the other two are not hooked to anything. Am i missing someting help? Mike
 

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I did the same thing, changed from an idiot lite dash to a guage dash, only my temp guage reads hot and I know its not. I changed my sending unit to the one its suppose to be but I wasn't able to get one that has a threaded terminal, they don't make them anymore, so I had to change the terminal on the end of the wire. I wonder if that has anything to do with it?
 

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Mike

The left \ right terminals are connected to the circuit card. The top \ bottom terminals have a resistor connected across them. The resistor should be orange or aprox. 86 ohms. The bottom terminal needs to make contact with ground \ metal back plate. When the gauge was calibrated did you send the sender along with it?

Jeffry
Not too long ago I purchased a temp sender from a local auto parts store. It was not the correct one for my 70. I then picked one up from a dealer. It is a Delco part #G1852. Additional #s on the box 4782L9 1 and 1# 12334869. The off brand part was about $6.00 The GM part was $15.00. It and the one on my car has a nail head connection. I don’t know if 72 would be different.

You can calibrate the gauge by placing the sender in a pan of boiling water, about ¾” deep. Connect the lead and ground. The gauge should read about 210 F
 

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Discussion Starter #6
Elree Colby,

My top and bottom terminals do not have a resistor across them. I think I got the right temp sensor, the reason I say this is the first one I had the gauge did not move at all the second one I put in, the gauge actually moved just to about the line above 100. The resistor is definitely not there where do I get one of these and how do I know which one to get. Thanks for you help. Mike
 

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My recently restored 69 factory gauges read very high on temp. It worried me, go I installed a mechanical AutoMeter gauge. The factory gauge is reading high. I have the correct GM sensor. I have heard that Permatex on the threads of your sensor can cause a bad ground a give a false reading, but I have not yet drained the coolant, cleaned the threads, and tested that theory. My factory oil pressure gauge reads pretty high, too, I was advised to look for a poor chassis ground as well.

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Mike Newby

69 Chevelle 355/TH200-4R
97 Grand Prix GTP
64 Chevy C10 Pickup
79 Suzuki GS550
 

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Mike

When correctly installed the resistor is under the circuit card. It is usually a white ceramic resistor about 1\8” thick, 1\2” wide and 1 1\2” long with two holes that line up with the vertical posts. It is color-coded on one side the one you need is orange it is 86 ohms. You can likely find one in a u-pull it wrecking yard. Look for a late 70s to early 80s Chevy\GMC truck with gauges. You will likely find it on the temp gauge.If you don't find one let me know I can send you one.
 

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Discussion Starter #9
Elree Colby,
I checked under my printed circuit board and there is an orange resistor attached from the top terminal to the bottom terminal as you said, My next question is will a bad ground cause is to not work. I did notice there is no ground to the bottom terminal of my temp gauge. Once again thanks for your help I really appreciate it. Thanks, Mike
 

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I was also having trouble finding the correct sending unit for my 70SS with gauges. I purchased one from GM with the nail head, it appeared to be for the idiot light setup. I checked the local napa and carquest and their part was exactly the same as the one from the dealer. I went to auto zone as a last resort and found the correct one in one of their books. they ordered it and I had it in two days. Works great and has the correct threads.
 

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Mike

The bottom post should be making contact with the metal back plate for a ground. If it is not the gauge will read high. It sounds like the gauge is good. I’m thinking the problem is with the sensor. Do you have an ohmmeter? The resistance should be around 450 to 500 ohms cold engine (80 F). At operating temp it should be about 80 ohms (210 F). Check with the person that calibrated it. Find out what resistance values were used.
 

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Discussion Starter #12
Elree Colby,
I was running my car pretty hard the other day the belt came off the alternator/ water pump/crank (Need deep groove pulley). The temperature gauge went up to about 200/210 I shut the car down. well my temperature gauge works but I think its reading to low how do I fix this problem. Thanks for your help,
Mike
 

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The easiest way to test is to go to radio shack and buy an 80 ohm 1/2W resistor. Disconnect the terminal to the sensor, wrap one lead of the resistor to this lead and the other to a GOOD ground. Turn the ignition key to on and your temp gauge should read around 210 degress. If it does your sensor is bad or not the right one. If it doesn't the problem is from the sensor back to the gauge or the gauge itself. If you can get to the sensor connection on the gauge remove it and attach the resistor from that terminal to the ground terminal on the gauge. If the gauge reads right you have a bad connection from sensor to gauge panel. If it still doesn't read right, check the gauge power lead for 12V, verify the resistance across the top/bottom terminals(86 ohm, you must remove the resitor to measure), and verify all connections to the gauge.

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Steve Strasemeier (70SS 396, Fathom Blue/White Stripes)
My 70SS
 
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