4R75E Trans Temp Comparison
 

Thought this info might be of some use

I recently installed an Isspro trans temp gauge in my '05 and installed it in the "hot" cooler line that goes out from the trans to the coolers. I also have a Gryphon Programmer and have TFT chosen as on of my four real-time readouts. The TFT reading on the Gryphon is what the PCM uses and the sensor is up in the valve body, but I never knew exactly what oil circuit it was reading... and no one could tell me. Maybe now I know!

The fact that the external gauge on the out line and the built-in sensor are reading exactly the same (so far) seems to say that the factory sender is reading cooler circuit temp... which will essentially be torque converter oil temp... because what goes to the cooler essentially is bled off from the converter. That's a good thing to know! After many discussions here (and elsewhere) I've changed my opinion about temp sensor placement (I used to advocate the pan but now cooler line outlet). If you have a programmer that offers these readouts (Edge Evo + Gryphon are two I know of), you may not need an additional gauge.

I will continue to monitor and see if the readings diverge in any situations, but thus far they are running neck-and neck and even change at approximately the same speed. My truck has 4.10 gears+ 33 inch tires and, FWIW, on a recently long trip at (solo about 70 ambient), the trans temp was rock steady at 150F on both gauges. I also towed about 10,000# of gravel in a dump wagon (at 30 mph) and both gauges read the same.

The temp sensor from the factoy on the 4R7X series transmissions is in the pan. On these newer vehicles it's built into the black plastic internal circuit board that attaches the case plug to the solenoids. On the older vehicles with this transmission, the sensor clips onto the valve body. Both of these setups will read the temp of the fluid in the pan only.

Just an FYI.

Darrin

Hey Darrin- The question, then, is why the two instruments are reading the same temperature? We're talking no more than about 1 degree different.

Are you 10000% positive that you have the temp sensor on the cooler feed line?

Can you post some pics maybe?

Darrin

100 percent sure it's on the outlet line. I have a remote mounted filter there (Racor LFS) and it has a port for a sender.

What I wondered about the sensor in the trans (never having seen it with my own eyeballs) was whether it might be tapped into the cooler flow circuit. My manuals don't show it's precise location. Anyway, I'm watching for a divergence of temperature that might tell something.

I don't have any pics with me as I am at a remote location doing a dyno day. But, I will post up a pic this weekend showing you the location of the sensor.

Honestly, it isn't tapped into any circuiit. It is simply on the board under the valve body and sitting in the fluid in the pan. Anyone who knows anything about these transmissions can confirm that. It's very common knowledge.

Darrin

Darrin- I believe you, though I would like to see the pics anyway.

The only possible explanation, then, is that I'm just not working the converter hard enough to get it's oil temp up beyond the baseline pan temp. Next time I get the chance, I'll get it warmed up and do some power-braking. That'll slip the converter and should spike that outlet temp higher than the pan temp. I tried that briefly, but I guess I didn't try hard enough. I'll bump this thread or post anew when I get it done.

hell, just city driving gets my temp to 180 and above

Possible causes for a difference:
1) tall gear ratio (mine is 4.10:1) will generate more heat because the converter will slip more and lock up later and less often
2) trans coolers (mine has the nine row HD cooler, plus a Mag-Hytec "DD"deep pan)
3) city driving will generate more heat than highway... more heat from shifting and converter slippage. On the highway, the converter is locked up and generating very little heat
4) driving style- I pretty much putt-putt around trying to save gas

Oddly enough, my rear axle temp runs hotter at 70 mph than the trans. My 10.25 semi-floater (with a Mag-Hytec cover) stabilizes at about 180 going 70 mph on a 75F ambient day. The trans is around 150 in the same situation. Lower gear ratios like 4.10s run somewhat hotter than higher ones like 3.55s, 3.73, etc.

I often drive with OD... getting that verter to lock in 3rd reduces heat by alot

That is what I see also. Just city driving, highway driving, and going up hills.

https://cimg1.ibsrv.net/gimg/www.f15...1b96eb32a1.jpg
https://cimg3.ibsrv.net/gimg/www.f15...45af7d6ff9.jpg