OEM thermostat. Never changed.

Those temperatures reflect all day use, and about an hour of drive time.

My truck is operating with 35" tires. Transmission is probably working harder because of that. Although I have always suspected the transmission cooler bypass valve of not closing.

GR is gear ratio on the Scan Gauge.

 

I've thought that also. But people more knowledgeable than me say that it's okay. Having all that extra data from a ScanGauge just gives me more to overthink. Apparently, after a dozen years of the same conditions, I have not suffered catastrophic failure. People with only the dummy gauge on the dash to look at, have nothing to worry about, and their trucks run just the same.

When my commute was only 10 miles, which took up to an hour in city traffic, transmission temperatures were lower. I do live in a city with hills. Going up & down steep grades, in stop & go traffic, is different than cruising on flat land.

For a few years, I had a twice a week commute for about 5 hours/300 miles each way. Highway speeds. Bumper to bumper, stop & go. Up steep grades. 1 horse towns with stop signs on the highway; causing me to stop for nothing, and then go wide open throttle to climb from 0 - 60. As i recall, transmission temps would climb as i went up grades, and the temperature would be high after 5 hours of doing that. Scangauge would show 220 - 225, if my memory is correct.

Right next to my house, I have a hill which climbs up about 1200 feet, within 1 mile. The bottom of the hill is a dead stop. The speed limit posted is 50 MPH. So I start in 1st gear, and the transmission works up to 3rd & 4th gear, as I go from 0 - 60 up hill. When I pull into my driveway, I allow the truck to idle as the fan runs, and the ScanGauge II displays the temperature dropping slowly. Would you be nervous if every day you pull into your driveway, the temp says 225? When do you turn the key off?

But the truck still runs fine. Dummy gauge needle on dash never climbs to red. Transmission has no hard shifting, or making any weird noises. I thought I had a transmission problem, but it turned out to be a misfire. Never had a transmission fault code. I don't see any leaking. I change the fluid, and the fluid is darker (which is normal wear), with fine particulate metal on the magnet (which is normal wear); but does not smell burnt, and there are no big pieces of metal.

I'm still toying with the idea to remove the transmission cooler bypass valve, to see if it would help keep temperatures down. Truck is 12 years old, and I haven't done it yet.

Transmission fluid exiting the transmission and going to the cooling line is hotter than the pan temperature shown on the ScanGauge. If I were to guess, I would say that the radiator is extremely effective, and already doing a great job of cooling the transmission fluid. Transmission line from radiator to auxiliary cooler is a little warm to touch. The auxiliary cooler has a temperature sensor switch on the inlet side set for 140. Transmission fluid from the OEM cooling system, and entering the auxiliary cooler is below 140, since the fan does not turn on, The transmission return line, from the auxiliary cooler back to the transmission is cool to touch. Even the bottom of the transmission pan is cool to touch. I think that the cooling system is working. Unless I can get more fluid out to cool, and have more cool fluid flowing back, I don't think there's much more that I can do. I don't know of any way to increase the transmission pump volume, or add larger cooling lines.