I've noticed that on my 2006 Duramax that I takes quite some time for the transmission temps to come back down. We just got back from a trip through Washington, Oregon, and into Northern California. Does the Allison transmission generate significant amount of heat when the rig and RV are descending a steep grade and the Tow/Haul feature is engaged and working?
The highest temp. was 225, but it was in the mid 90's, so 225 is a reasonable tranny temp when pulling mountain passes.I'm running Amsoil synthetic tranny fluid.
Also, I've read numerous posts that discuss the tranny "locking". How can you tell when it's "locked"? I'm assuming when it gets into 6th gear, is that correct? I don't know of any other way to tell if it's locked or not.
Tow/Haul plus grade braking does generate heat. 225 is not out of line. Normally about 100* above ambient temp.
Just came back from a trip to Payette National Forest with my 14K fifthwheel toy hauler starting in Seattle and going to McCall, Idaho via I90, WA-26, 12, 95 and ID-55 going and ID-55, 95, 12, WA-261, WA-26 and I90 returning. Saw 200* tranny temps between 80-90* ambient pulling/decending grades like White Bird Hill and the Lewiston grade which are between 7 and 8% for a few miles. Nothing that steep on I-5 in Washington/Oregon/north CA.
Your torque converter locks up in all gears above 2nd if in T/H. Running 6th gear at any speed less than about 62 with stock tires is borderline lugging and will build extra heat - coolant, transmission and exhaust temp.
Make sure your fluid is not overfull!
160* on tranny gauge -dipstick should show fluid in the lower "hot" hatched section.
180* on gauge -fluid in the middle of the "hot" hash
When the Tow/Haul button is engaged, your tq converter is locked up, this changes the shift points as well as pushing your fluid through the cooler at a constant rate. Higher temp can also be a result of all coolers, tranny/ a/c and rad, being clogged up with dirt and debris.
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Hope you don't leave it in auto when creeping up hills.With the six speed down shift in manual to 5 or 4 Depends on rpms.
I never use TH.But I also have Efi live with tow tune
2007 chevy 3500 ltz CC LB Duramax
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carpetguy2 wrote: With the six speed down shift in manual to 5 or 4 Depends on rpms.I never use TH.
Why? The Allison is computer programed and quite smart about shifting to the proper gear on its in own. The T/H will save your tranny and should always be used...
If you are towing or hauling, you should be using tow/haul. They put it there for a reason. As far as the tranny staying hot, *I think* what is happening is the coolant temps drop fast (more or less coasting down the hill) causing the engine thermostats to close, more or less cutting off coolant flow in the radiator. The allison has a cooling loop in one of the end tanks of the radiator that does most of the work as far as cooling the tranny, but with coolant flow cut off, it just sits there bathed in very hot coolant (the trapped coolant is about the temp it was as you crested the hill). As soon as you start burning fuel again the tranny temp dropped like a rock - right?
As long as you are above ~48mph it is locked, it unlocks at ~45. In tow/haul it locks and unlocks midway through second.
* This post was
edited 08/02/12 10:17pm by christopherglenn *
Does the GM have the Trans cooler underneath the truck (drivers side) with an electric fan? Verify the fan works and the cooler isn't caked. Buddy has an lbz he bought used with the cooler under the truck, I didn't think that would be stock...
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Thanks for the input, I've been wondering about the "locked" issue for a while now. Nice to know the rest of the story.
The transmission temp did ease down on the flat land, we were coming over this Syskiyou's. I watched it also pulling up out of Biggs, going towards Goldendale. Temps were all within specs, so no issues. I figured that the descent has to generate heat, which can be soaked up by the brakes, or by the transmission (then out through the cooling system), but it has to go somewhere. You can just make energy disappear.
. . .With a 6 year old vehicle you can expect some blockage on the inside & outside of the radiator ( MOSTLY on the airflow / outside of the radiator ); Also AIRFLOW BLOCKAGE has happened to the A/C Condensor & CAC (Charge Air Cooler ); This results in a slower dissapation of heat buildup & also more pronounced temp readings under a load / high heat days. Best solution would be to have a QUALIFIED Radiator Shop Check out system. DO NOT USE a Power Washer as bugs SWELL up when they get wet & are harder to BLOW out when swolen!!!
boogie_4wheel wrote: Does the GM have the Trans cooler underneath the truck (drivers side) with an electric fan? Verify the fan works and the cooler isn't caked. Buddy has an lbz he bought used with the cooler under the truck, I didn't think that would be stock...
The stock cooler is mounted in front of the ac condensor, in the bottom 1/3 of it. I know of no stock electric fan on a duramax pickup other then the fuel cooler, under the drivers butt & in front of the fuel tank.
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