I checked on the 180 degree fluid temperature in the pan figure. Jim, from ATO Transmissions, says the 48RE transmissions he builds typically run 15-25 degrees cooler than the stock 48RE, mainly because of the extensive use of Torrington thrust bearings instead of thrust washers. With his transmissions, the primary source of heat generation is the front pump, in addition the planetary gears are always under thrust and producing a minimal amount of heat.
Most of the heat is generated by the torque converter when it isn't locked up. The valve body converter feed circuit supplies pressurized fluid to the converter. As soon as the converter is completely full, the fixed vane impeller starts driving fluid through the turbine, after which it goes through the stator (which acts as a torque multiplier) and then the fluid goes to the cooler(s) and back to the transmission. The heat is created primarily by the friction of the fluid striking the vanes of the turbine. Heat can build up quickly when the truck is accelerating a 25K pound load or pulling a long grade.
Which torque converter is used and where the stall speed is set will have a big effect on fluid temperature. If the torque converter is set up with a higher stall speed, it will generate heat faster than if it is set up with a lower stall speed. The lower stall speed results in improved fluid coupling between the impeller and the stator, which improves efficiency as well as generating less heat.
It is always good to have the temperature sensor in the transmission oil pan. The cooler return line to the transmission carries the fluid after it has circulated through all the internal components of the transmission. After the fluid has returned to the pan, the temperature sensor can now show the lubricating temperature. (The lubricating temperature is the temperature of the fluid being supplied to the transmission components). The temperature sensor on the return line before the transmission will not show lubricating temperature, or if the temperature sensor is on the out line before the cooler it will read very high temperatures. If these temperatures are important, simply use a two way toggle switch for temperature out and temperature in. With everything working correctly, the transmission fluid temperature should run between 150 and 180 degrees. If the transmission is worked hard enough, the fluid temperatures will go higher. Never let the temperature exceed 280 degrees on the return side of the cooler.
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