Transmission Temp Gauge Install 1996 C2500

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DonF

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I did my transmission temp gauge today. I followed the guides here.
https://www.gmt400.com/threads/how-to-install-a-trans-temp-gauge-in-a-95-gmt400-with-a-4l60e.17168/

It was very helpful, but there were a few changes. The thread starter had problems installing the trim back with the pod mounted low. I wanted the pod low also so I ran the wires, then drilled the hole for them to exit. The hardest part of the job was getting that trim piece back in place without breaking anything. I tried last night and after messing with it for a long time I just went to bed. This afternoon it went back in with just a few minutes of fiddling. Once the trim piece is in place, the holes can be drilled with an angle drill. I had to leave a little gap between the pod and dash because I drilled the wire hole too high after reading the tips in the older thread. Still I am pleased with how it turned out. The chime box does not have to be removed. The necessary pins are all right there out in the open. Scored the B&M gauge as part of a returned amazon warehouse deal for $14.40 shipped. The gauge is a cheaply made imported gauge with a B&M logo on it. Still for the price it works fine. I would not pay full price for it though. I think Autometer or VDO are much better quality. I tig welded a bung in the pan. It looks like it hangs down, but the factory exhaust is much lower than the sensor. I did not paint the pod. I figured there was enough black trim in the interior that it would blend in fine. No one is going to mistake a gauge pod with a BM gauge as factory anyway.

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Supercharged111

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I used the pressure test port for my sensor. I think it's SEM who makes an interior paint that's a damn close match to that grey. I got it at Napa 100 years ago. It's educational to see what makes the trans hot and how cool it will run with just factory coolers.
 

DonF

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Learning around 1993, I used to work right next to the transmission guys at the local GM dealership. They would have me do trans temp gauge installs back then using the pressure test port. The head tech said while he understood why they did it on customer cars (fast = cheap), he would not recommend that for his own vehicle. The fluid on the pressure port is a dead end and not part of the flow. More of a case temp sensor that way than fluid temp. I tried it both ways previously, both work but there is a temp difference between the two sensor placements on the same vehicle.
 

Hutchinson

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On my 4L60e, I got the deep aluminum pan, drilled/ tapped the pan and installed the sending unit (to the Autometer gauge) in the pan (on side, bout 1/2 way up),.... I wanted to read the oil temp going up into trans, since I wasn’t racing,...... the racing guys wanna see temps coming out of their trans to cooler, but, that’s not an issue with me. I thought about the pressure port tap up top too, but, I though,..... shoot man, all I’ll read there is case temp (not get the real oil temp).

If I do race it in the future, i’ll put a 6AN “T” on the discharge line going to my 40K coolers,.......what am I talking bout,...he’ll, I’m bout to swap the auto for an NV4500 Manual, sorry fellars.
 

Supercharged111

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Was it higher in the test port? I never knew it was a dead end there, but I was under the impression that it read higher than the pan.
 

DonF

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Was it higher in the test port? I never knew it was a dead end there, but I was under the impression that it read higher than the pan.
No at the test port the temperature is mostly affected by case temp. The fluid path is just a little finger and goes nowhere. Its shown in GMs oil path diagram. Its slower to react hotter or cooler and usually lower than the pan. The when the sensor is put in the cooler line, temps can vary a lot depending on if it's before or after the cooler and how hard your pushing it. The pan temp measures the fluid temp that the transmission is pulling through the filter and its sort of in between the two.
 

DonF

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Another advantage to the pan mount sensor bung is now its a way to drain the fluid before dropping the pan. Much less mess when the pan is empty.
 
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Supercharged111

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I have noticed that it takes a long time for the temp to drop after getting hot. I figured that's just how long the fluid took to cool off. My pan does have a drain plug though. Now you have me curious about my trans temps. How much cooler did you observe with the sensor in the case?
 

DonF

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The most accurate way of comparing would be to run two sensors with two gauges at the same time. I never did that. So all the other factors play a part, air temp, trailer load, ect. On my van between the two locations on a road I pulled a trailer on often... I would guess 10-15 degrees. The more noticeable part is how fast it reacts. The dealership always put them in the pressure port and you can see when the trans is getting hot over time, just not as responsive as putting it in the pan. The electronic GM transmissions have a temp sensor in the pan to use for the shift control and hot mode. Not the most accurate, but if you have a scan tool with that pid you can compare to what you are reading now.
 

L31MaxExpress

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I put mine in the cooler line exiting the trans. The hottest fluid is in the converter. My pressure test port has an VDO 0-300 psi line pressure gauge installed. The fluid leaving the converter is often 50°F hotter than the fluid in the pan using the OEM sensor reading. Going down the highway with a locked converter they are very similar though.
 
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