lb7 transmission temps - Chevy and GMC Duramax Diesel Forum
01-04.5 LB7 Duramax Powertrain Discussion of components that are directly involved in the power production and all that is needed to get and keep the truck moving . Engine , Transmission Ect

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Old 09-12-2011, 11:33 AM   eBay Motors  #1 (permalink)
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lb7 transmission temps

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 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. 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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Old 09-12-2011, 11:34 AM   eBay Motors  #2 (permalink)
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100* over outside temp is where the tranny where run
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Old 09-12-2011, 11:35 AM   eBay Motors  #3 (permalink)
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Have you checked the fluid level and made sure it is properly filled?
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Old 09-12-2011, 11:37 AM   eBay Motors  #4 (permalink)
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Tranny temps are usually 100 degrees over ambient. the OE gauge for coolant temp is wrong more than it is right. If you have a scanner capable of reading it, go off that.
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Old 09-12-2011, 12:09 PM   eBay Motors  #5 (permalink)
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fluid is normal... I believe higher than the marks when shut off and right where it should be at idle. Truck shifts and drives fine. If the gauge was out, why does the cooling fan keep coming on to the point that it actually cools down the engine temps? on a wamn day (15-20degC) this is close to what I am seeing, however if the temps get about 25-30 (80-90deg F) outside this is when I see the guage get high.
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