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Old 08-30-2021, 05:57 PM
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Default Temp gauge HELL in 76 TA


Working on a 1976 Trans Am. I've installed a new temp/oil gauge, printed circuit board and new sending unit. Oil pressure is dead on, temp is off by 80 degrees. These are new parts from our host. Grounded temp lead at the engine and gauge will peg out as it should.

I have traced all the wiring and connections and all look good. Ohm out wire, no resistance. New ground strap from frame to engine and made sure cluster is grounded. I installed a temporary overlay wire for the sending unit to the cluster. Still 80 degrees off. Sender is correct button type sender from Ames. Also tried a sender from Summit. Cleaned out mounting hole in intake manifold and installed sender with copper anti seize. Anyone got any smart ideas what it might be? I'm ready to sucker punch the cluster!

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Old 08-30-2021, 08:56 PM
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Please tell going through the same thing, its 60 degrees off!!! Literally just did what you said 2.5 hours ago.

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Old 08-30-2021, 09:51 PM
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I'm going through a little temp hell myself. I have fuel injection so the original gage is hooked up normally then the FI has it's own sender and I can read the temp in the FI's handheld. I have electric fans so engine temp fluctuates with fans kicking on and off. My factory gage always reads the highest temp my engine reaches. So as temps swing the gage never goes down. On a complete cold start the gage starts low as it should and works its way up as temp goes up.

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Old 08-30-2021, 10:22 PM
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Just curious what’s direction is it off to? Reading hotter than actual temp or less than actual temp?

I haven’t got a clue where the sender came from in my car, it was there when I bought it, but it isn’t original. Parts store senders are notorious for being inaccurate. I read on this forum about lectric limited and ordered one from them. Comparing the temp gauge with new sender to a mechanical gauge and water crossover temp with an infrared thermometer, they’re all real close now.

My other sender read around 50° high. You can test the senders if you wanted too. They should a specific ohm reading at different temps.

It also seems to me 79 or 80 required different senders with different ohm ranges. Just FYI to the second two posters who didn’t mention what year their car was.

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Old 08-30-2021, 10:34 PM
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My gauge is reading about 60 deg hotter. It is a 77 400 transplanted in a 81 TA.

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Old 08-30-2021, 11:26 PM
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Quote:
Originally Posted by 4dblnkldude View Post
My gauge is reading about 60 deg hotter. It is a 77 400 transplanted in a 81 TA.
Ok. That’s similar to how mine was. 50-60 degrees hotter than my mechanical gauge.

Looking at lectric limited’s site, 77s with Pontiac motors are a different part number than 79s and 80s with Pontiac motors which are the same part number. Obviously the 400 wasn’t available in 80 but it’s the same part number for the 400 or 301 which I believe is because the gauge in 79-81 cars is set up differently and requires different resistance than earlier gauges at the same temp.

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Old 08-31-2021, 07:56 AM
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The only temp sending units that are even close are the Lectric Limited or old NOS Delco. The others are way way off. Our parts retailers need to stop selling them, and sell an accurate part.

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Old 08-31-2021, 09:08 AM
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1st are you using a sending unit FOR a 1980 TA....no matter the engine. You may need to adapt the CORRECT sender to fit YOUR intake but you must have the sender for whatever yr the GAUGES are.

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Old 08-31-2021, 09:25 AM
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Quote:
Originally Posted by bhill86 View Post
Just curious what’s direction is it off to? Reading hotter than actual temp or less than actual temp?

I haven’t got a clue where the sender came from in my car, it was there when I bought it, but it isn’t original. Parts store senders are notorious for being inaccurate. I read on this forum about lectric limited and ordered one from them. Comparing the temp gauge with new sender to a mechanical gauge and water crossover temp with an infrared thermometer, they’re all real close now.

My other sender read around 50° high. You can test the senders if you wanted too. They should a specific ohm reading at different temps.

It also seems to me 79 or 80 required different senders with different ohm ranges. Just FYI to the second two posters who didn’t mention what year their car was.
The TA has FAST EFI installed. The handheld programmer will show 180 with the cluster temp showing 100. I have verified the programmer temp reading with an IR gun. I just ordered the #01513321 sender from Lectric Limited and will give it a shot.

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  #10  
Old 08-31-2021, 01:23 PM
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All those imported gauges are not tested/calibrated using a sender that is because aftermarket senders all vary because none of them are made to the GM standard. The imported gauges are not exact, they are copies and they are not all made accurately. They sell "new" gauges for many different (years) GM car restoration projects. Add to that some GM cars with gauges are labeled Cold-Hot (1968 GTO for example) and others are labeled 100-250 ('69-72) GTO. The trans am temperature gauge for 1970-72 was labeled: 100-210-250. When they added a restriction (catalytic converter) into the exhaust system in 1973/74 they changed the thermostat to a 195. Those Trans Ams have a temperature gauge that reads: 100-220-260.

There is no way the aftermarket (1/2 way around the globe can keep track of all these changes). Those people do not have a shop manual for your car over there. There are no cars like your car over there for them to go and look at!!!

The people who make new temperature senders are not the same people who make reproduction gauges (that never read true anyway). Modern aftermarket replacement senders are all "combined" today. For a car that is 40 or 50 years old, they can't spend a bunch of time on something they might sell maybe 100 or 150 of in a year. That is where they take what may have been a half dozen original GM #s and combine all those into one "replacement" part #. So right there we have another calibration issue.

I have been a GM mechanic for over 42 years. I can test & calibrate any temperature gauge (electrical) out of any old Pontiac with "factory" option gauges.

I make up a (real world) test on my bench which includes a 12 volt DC battery, 4 or 5 jumper wires, boiling water, a thermometer and the gauge plus several different senders in the water all at once to determine which one gives me the best readings. I have calibrated over 100 temperature gauges for customers (all across the USA) with lots of different year Pontiacs using this method.
As long as your GM gauge is NOT missing it's pointer; has not been dropped and broken, or left outside in the rain; there is a 98% chance that I can repair it here using USA made parts.

You can always PM me in case of any questions.

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Old 08-31-2021, 02:03 PM
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Quote:
Originally Posted by Peter Serio View Post
AThe trans am temperature gauge for 1970-72 was labeled: 100-210-250. When they added a restriction (catalytic converter) into the exhaust system in 1973/74 they changed the thermostat to a 195. Those Trans Ams have a temperature gauge that reads: 100-220-260..
Catalytic converters were added in model year 1975. EGR was added in 1973.

My unrestored 1973 Formula had the 100-210-250 temp gauge.

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  #12  
Old 08-31-2021, 02:19 PM
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Quote:
Originally Posted by Peter Serio View Post
Those people do not have a shop manual for your car over there.
Even if they did have the appropriate shop manual, I don't remember charts in the original shop manuals that had X ohms at Y degrees for various temperatures.

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Old 08-31-2021, 04:59 PM
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Default Temperature gauge Chart in Ohms.

This is from a Kent Moore tester:

Note that this chart does not even list the early (2nd Gen.) trans am temperature increments. (210 at the 1/2 scale.)

I stand corrected; my point however it happened is that the "normal" underhood temperatures increased by the added EGR valve and then again even more by the addition of the catalytic converter.

At least that is my theory on the center line; painted # going from 210 up to 220 degrees on the 1970s Pontiacs.

Same deal on the big end 250 to 260.

After 1973 I do not believe that those early gauges were available to order from GM anyway. Those temp gauge 100-210-250 markings may have only come on cars "as built." If you needed a replacement gauge, say in 1978, for a 1972 Trans Am. The original part # for the early cars was superseded by the 100-220-260 version.

And all that the aftermarket sells today is the 100-220-260 version.


Just FYI, photo posted here was automatically reduced in file size to the point where it looks blurry. My original jpeg is not.
I have the original; and it is big enough that it will print well enough to read, probably not from here.
If you need to print it out just PM me with your EM address and I will EM you the big file size!
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Last edited by Peter Serio; 08-31-2021 at 05:05 PM.
  #14  
Old 08-31-2021, 06:25 PM
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Quote:
Originally Posted by 67Fbird View Post
1st are you using a sending unit FOR a 1980 TA....no matter the engine. You may need to adapt the CORRECT sender to fit YOUR intake but you must have the sender for whatever yr the GAUGES are.
If I wasn’t clear, that’s the point I was trying to make when suggesting the Lectric Limited senders.

  #15  
Old 09-01-2021, 12:29 PM
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Quote:
Originally Posted by Peter Serio View Post
This is from a Kent Moore tester:

Note that this chart does not even list the early (2nd Gen.) trans am temperature increments. (210 at the 1/2 scale.)

I stand corrected; my point however it happened is that the "normal" underhood temperatures increased by the added EGR valve and then again even more by the addition of the catalytic converter.

At least that is my theory on the center line; painted # going from 210 up to 220 degrees on the 1970s Pontiacs.

Same deal on the big end 250 to 260.

After 1973 I do not believe that those early gauges were available to order from GM anyway. Those temp gauge 100-210-250 markings may have only come on cars "as built." If you needed a replacement gauge, say in 1978, for a 1972 Trans Am. The original part # for the early cars was superseded by the 100-220-260 version.

And all that the aftermarket sells today is the 100-220-260 version.


Just FYI, photo posted here was automatically reduced in file size to the point where it looks blurry. My original jpeg is not.
I have the original; and it is big enough that it will print well enough to read, probably not from here.
If you need to print it out just PM me with your EM address and I will EM you the big file size!
Thanks for the chart Peter, this will help give me a better idea of what's happening. 👍

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'21 Chevy 4X4 Crew RST Z71
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