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Discussion Starter #1
hello, I have a 2004 lb7 2500HD crew cab 4x4 duramax with 170,00kms (110,000miles) that is stock except for a bully dog programmer running on economy mode. I bought the truck used so this is my first summer with it. My transmission temps seem very dependent on the outside temp. If the outside temp is 30 deg C (90 deg F) the transmission with heat up to about 95 deg C (203 deg F) in traffic in the city or driving slow and about 90 deg C (195 deg F ) on the highway. However on a recent drive the temp dropped from 30 deg C to about 16 deg C (60 deg F) outside and the transmission followed down to about 65 deg C ( 150 deg F). In the winter the gauage almost does not move at all off 40 deg C. This is all with no pulling a trailer or any significant hills. If is annoying because as the trans temp rises the engine cooling fan kicks in. The actual engine temp always stays right around the middle or falls off to about 1/4 while the fan is on cooling the transmission temps. Is this normal? It seemed to have got a little better after I pressure washed the cooler and removed the aftermarket grill, but the fan still comes on quite a bit in normal driving when it is hot outside. I am almost worried to tow a trailer on a warm day and have the transmission overheat. How can I fix this and lower the transmission temps?
 

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Discussion Starter #3
why does the cooling fan come on so much? I'd think that would be saved for when its actually working hard pulling up a steep hill.. not crusing on the flat highway at 70mph?
 

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The trans temperatures are normal.

The engine cooling fan is controlled by a bi-metal spring sensor in the face of the fan hub. The HEAT through the stack affects the sensor and operates the fan. If the stack-[oil cooler, AC condenser, inner cooler, and radiator] are restricted by leaves, and dirt, the fan will operate more, because the air through them is hotter than normal.

The fan will operate for a little in the morning, until the fluid in the fan hub is warmed, and then will free wheel. Normal operation of a viscosity unit.
 
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