My 6.5 diesel Banks turbo’ed 1987 V20 Suburban has a 4L80E and 3.73 axles with 315/70 tires. My Compushift transmission control module has a temperature read out. I do not know where the sender is for that temperature. It gets it from the factory 4L80E harness plug.
Living in flat land Texas I see temperatures outside over 100° daily every summer. The 4L80E normally cruises down the highway empty at 70 mph with the torque converter locked at around 170°. Pulling a 10,000 pound trailer in 3rd with the torque converter lock engaged at 60 mph will get the temperature up to 190° or sometimes up to 200°. Never more that a minute or two though.
I thought that was normal and all good. Then I spent 2 weeks driving the truck around the mountains of Colorado last month. I was hitting 200° - 212° on mountain passing going up in 3rd. 185° - 200° going down mountain passes in 2nd. Using the brakes a lot. 200° - 225° on any trail up or down, high or low transfer case. Outside temps were never more than 80°.
Those transmission temperatures just seem awfully high to me. So high that I didn’t do some trails I wanted to accomplish because I was worried about my ability to drive the truck 1200 miles or more back home.
Part of my problem is ignorance. What is the normal operating range of a 4L80E? What is considered hot? I have the transmission lines plumbed first to the radiator and then to the biggest stacked plate cooler I could fit before going back to the transmission. I built it that way thinking it would provide a more steady temperature and not shock the transmission too hot or cold depending on what I was doing and changing outside temperatures. I need to note that anytime the transmission was hot by my standards it never exceeded the engine coolant temperature by more that 5°. I evolved during the trip to higher and higher engine rpm to keep coolant temperature down which seemed to help the transmission temp as well.
Thoughts? Thanks.
Living in flat land Texas I see temperatures outside over 100° daily every summer. The 4L80E normally cruises down the highway empty at 70 mph with the torque converter locked at around 170°. Pulling a 10,000 pound trailer in 3rd with the torque converter lock engaged at 60 mph will get the temperature up to 190° or sometimes up to 200°. Never more that a minute or two though.
I thought that was normal and all good. Then I spent 2 weeks driving the truck around the mountains of Colorado last month. I was hitting 200° - 212° on mountain passing going up in 3rd. 185° - 200° going down mountain passes in 2nd. Using the brakes a lot. 200° - 225° on any trail up or down, high or low transfer case. Outside temps were never more than 80°.
Those transmission temperatures just seem awfully high to me. So high that I didn’t do some trails I wanted to accomplish because I was worried about my ability to drive the truck 1200 miles or more back home.
Part of my problem is ignorance. What is the normal operating range of a 4L80E? What is considered hot? I have the transmission lines plumbed first to the radiator and then to the biggest stacked plate cooler I could fit before going back to the transmission. I built it that way thinking it would provide a more steady temperature and not shock the transmission too hot or cold depending on what I was doing and changing outside temperatures. I need to note that anytime the transmission was hot by my standards it never exceeded the engine coolant temperature by more that 5°. I evolved during the trip to higher and higher engine rpm to keep coolant temperature down which seemed to help the transmission temp as well.
Thoughts? Thanks.
