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Discussion Starter · #1 ·
I have a 2500HD, towing package, Duramax LBZ engine with the 6 speed Allison transmission. Last week I had a 33ft 5th wheel (approx. 15,000 loaded) and traveling approx. 70 mph I had the Allison overheat and the fuel air mix cut my power down dramatically several times. It was about 97 degrees F. I lowered the speed to 60-65 and the issues subsided. Has anyone else experienced this? Do they make an upsized transmission cooler?

I'm kind of pissed that I bought the biggest engine /transmission package available and then had other truck/trailer combinations with similar weight ratios shooting by me while my trouble light was on and the power was shut down to 60% or whatever. :mad:
 

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i never have heard of a LBZ overheating in any way,i have a friend that tows heavy(20k to 25k pounds)3 or 4 X's a week with his 07 S/C L/B DRW Chevy LBZ and all of it's on the highway and never had any trouble with overheating..i'm sure they have stuff avalible..have you changed the fuel and external tranny filter lately?
 

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Were you using tow/haul? It shouldn't have mattered though since you were cuising at highway speeds. You might want check the fluid level. There is a guy that has an aftermarket tranny cooler..His user name on here is MikeL and he is an allison guru or expert whatever you want to call it. You don't have a bunch of bugs or dirt in the tranny cooler do you? So, what was the temp of the allison and your engine temp. Did you burn the tranny fluid? If you did truely overheat the allison, change over to some synthetic tranny fluid while you're at it.
 

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Discussion Starter · #5 ·
The unit was running about 225-250 (I think.....I'll look at the gauge when I get home to verify). When it got to 250 (3 times during this trip) the fuel/air mixture would automatically shut the engine down to 1/2 or 3/4 power until the unit cooled down (very bad when you are on a long hill in heavy traffic). I started running at 60-65 and the transmission stayed below the "power cutoff/overheat protection point". I stopped at a carwash and sprayed the tranny cooler coils just in case they were dirty. By the time I had done this the outside temp had dropped to 93F so I don't know if it really helped. I am going to put some Amsoil synthetic into the tranny ASAP but I would also like to increase the tranny cooler size if I can find someone who has had some experience with this.
 

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Well, your tranny could have been over/under filled from the factory. That could have caused your problem. Hopefully it isn't nothing major though.
 

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I had the Allison overheat and the fuel air mix cut my power down dramatically several times. It was about 97 degrees F. I lowered the speed to 60-65 and the issues subsided.
could you hear your fan running a lot? Was the coolant gauge on the rise?

There are some reports of the LBZ having a hard time with some conditions, but better than the 04-05 LLY.
 

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normal operating temp on the six speed is 185 - 220 with a 235 limp reduction to kick in, tranny takes 7.4 quarts of dex 6 with the spin on filter, the only time he said to change the internal filter is if the tranny is rebuilt but i do it anyway. he said they have had trouble w/ the temp gauge being off 10-15 deg too
 

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Discussion Starter · #9 ·
The engine temp was normal throughout this trip. The transmission temp would run slowly up to about 200 and then go into limp mode. If I could slow down to keep it below 200 it would continue to run OK. The transmission temp gauge may be off but I am wondering if I have a bad over-temp sensor (connected with the limp mode but not the dash temp gauge) that is reading hotter than it should thereby shutting me down well before it should. I'm not sure why the gauge sensor wouldn't also control the limp mode, but it might be two separate systems. Any thoughts?
 

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There is no fuel limiting limp mode associated with the transmission, to the best of my knowledge. Your problem is not related to the allison temperature.

What was your EVT, and what year vehicle do you have? You need a signature.
 

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When you put that Amsoil ATF in consider a Mag Hytec transmission pan. It holds more fluid, and is made of finned aluminum. Aluminum dissipates heat faster than steel, and with the extra fluid capacity, can help reduce max operating temps.
 

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Discussion Starter · #14 ·
I took the truck to a dealer yesterday and they said the engine went into limp mode because of a fault in the PCV valve that would heat things up. They said it was somewhat of a design fault that they had been programming around. .............We'll see.
 
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