Hi Guys,
I just got the truck about 6 weeks ago, and I don't know much history on it. 2002 HD Duramax / Allison 193,000 miles I believe it is stock.

Truck seems to have no problems when unloaded.
When I have my trailer attached (9500 # and not aerodynamic at all) I overheat the tranny. I ran 60MPH for 70 miles, and had to pull over because trans temp guage read 265* and the dash said Transmission overheat (or something equivalent). Let the truck sit for about 45 minutes tranny temp was down to 200*, and continued on the trip at 55 MPH with no problems at all (except SES light) for the rest of the trip (60 miles). Temp held a constant 200*.

On the return trip (the next day) I decided to try to take it easy on the trans. and run 55 MPH all the way home. We got about 20 miles down the road, and the temp was at 225* so we pulled off, and unloaded the trailer.

I had to have my Father in law pull the trailer home with his v-10 excursion :o:.

I had Just changed the fluid (drain and fill) with Transynd, but I do not do a complete change.

Sorry for the long post.....Any ideas on where to start?

make sure that it is not over full. having an overfull allison is just as bad as not having enough fluid. it should be no more than half way up the full mark when at operating temp in park while running

Check your fluid level... Overfilling these Ally transmissions will cause the tranny to get hot especially when towing... Do a search and you'll see most folks with overheating trannys are a result of overfilling the tranny

When you changed the fluid, you changed the external filter as well?

Ditto on the fluid level. If you do change the spin on stay with the Allison brand! ;)

Check your fluid level... Overfilling these Ally transmissions will cause the tranny to get hot especially when towing... Do a search and you'll see most folks with overheating trannys are a result of overfilling the tranny

When you changed the fluid, you changed the external filter as well?

Sorry, I should have noted that the fluid level was correct.
Yes, the spin on filter was changed. Also worth mentioning the old filter did not have a magnet. I haven't gotten one for the new filter yet:o:.

Ditto on the fluid level. If you do change the spin on stay with the Allison brand! ;)

The filter I got wasn't Allison brand, but I did get it from our local Allison dealer. The filter that they gave me is an ABP / N10G-29539579.

again when you say it was correct make sure that it is no higher than the middle of the hot marks

again when you say it was correct make sure that it is no higher than the middle of the hot marks

Right! ...and be sure the trans temp is 175-180F when you check it.

I checked the level again last night, but was only able to get up to 150*. Level was in the bottom 1/3 of full hot range.

As this problem only happens while towing, is there a chance 5th gear is slipping under load? Service engine soon light was on for a couple of days, but it went out.

What was your engine temp when the transmission was hot? Was the engine fan runnming? Get one of those infared guns and check the transmission cooling lines. If they are not hot there may be a blockage in the transmission cooler or too much restriction in the transmission filter.
Find a Allison dealer they have the filters at a reasonable price. I got some for less than $10 each. They were Allison filters. Good luck.

What was your engine temp when the transmission was hot? Was the engine fan runnming? Get one of those infared guns and check the transmission cooling lines. If they are not hot there may be a blockage in the transmission cooler or too much restriction in the transmission filter.
Find a Allison dealer they have the filters at a reasonable price. I got some for less than $10 each. They were Allison filters. Good luck.

Thanks for the reply.
Engine temp was under 200* while towing. Good idea about the infared camera, I will try that (I have one at work :D).

Another item. Where you in tow Haul? Tow Haul will help keep the torque converter locked which will help lower the transmission temperature. If the transmission clutches are slipping I doubt the transmission will last long and I would expect the Allison to put you in limp mode if the clutches are slipping enough to cause you to overheat.

Another item. Where you in tow Haul? Tow Haul will help keep the torque converter locked which will help lower the transmission temperature. If the transmission clutches are slipping I doubt the transmission will last long and I would expect the Allison to put you in limp mode if the clutches are slipping enough to cause you to overheat.

yes I was in Tow/Haul mode. Also, I never heard the cooling fans kick on.

You're probably going to be slightly overfull when heated to the proper temp. I'd recommend changing the spin-on without adding any more fluid.

The characteristics of being overfull are a rapid rise in temperature and oil spewing from the vent cap at the top rear of the trans.

You're probably going to be slightly overfull when heated to the proper temp. I'd recommend changing the spin-on without adding any more fluid.

The characteristics of being overfull are a rapid rise in temperature and oil spewing from the vent cap at the top rear of the trans.

ok, thank you. that is exactly what I saw when I pulled over when the temp was @ 265* (fluid running out of the overflow). I had checked the level when changing to Transynd, but I just filled it to the "full cold" mark. It was 7qts.

I sure hope this is the problem.
I sure THOUGHT that I had the level correct. I guess that shows how little I know about this truck.:o:

Thanks for the help guys.

Would this cause some fluid to appear to be leaking from the "seal" between the Allison & the transfer case? Mine has been leaking some fluid for quite some time, lands on the crossmember, and the leak appears in 4-5 spots in a straight line, side to side.

Is 1 1/2 quarts over the full hot mark too much????????

That is what the dealer did for me. Just had the tranny lines replaced and the next trip the tranny temp went to 250. Drained out 1 1/2 quarts to get in line. No more problems since, however the dealer told me there is nothing wrong with the fluid after being that hot. I am going to change it just for peace of mind.

Change Dealer Immediatly !!

Where exactly is the overflow located?

Where exactly is the overflow located?

Breather/vent is the silver cap at the top, driver side, rear of trans. It is located just forward of the rear cover splitline.

Breather/vent is the silver cap at the top, driver side, rear of trans. It is located just forward of the rear cover splitline.

Good morning.
Ran into an interesting overheat problem on an '05 Duramax yesterday.
Customer called me and said he was reaching close to 300F on his trans gauge. he said both cooler lines were cold at the cooler. I had him do a flow test at trans and it had a good streem. He noticed line going to radiator had a slight leak at the crimp in hose. He wiggled it and heard what sounded like a purge. Rubber hose was found to be collapsed. Temps dropped after the purge sound. I have not run into this yet and thought you might like to know.:D

That is interesting. I'll have to see if I can repeat it. Do you know if the support bracket was attached to the engine block under the ex manifold? I've seen some of the early 2006's that had cooler lines mis-routed, but no 05's.

**UPDATE**
This is the first time I have had a chance to tow my trailer since the last overheat problem. Fluid level OK. Transynd Fluid (has been hot once). Tow haul mode. transmission started to overheat 25miles into the trip.

I pulled over, let it cool down, and continued the trip. This time I didn't let the tranny shift into 5th.

The truck did great in 4th. Ran 200* the whole way. Return trip was the same (ok if in 4th)

This is an '02 what is the best way to disable overdrive?

FWIW, I just did a deep pan at the Allison dealer and it dropped the tranny temp another 10 degrees. I have to tow to get mine above 165. The pan and 5 gal fluid (transynd) was $236 and tax.

Doug

Just to update an old post:
My problem turned out to be a sticking solenoid in the valve body (solenoid E). This is the Solenoid that shifts into 5th. I could set the cruise @ 54MPH with the trailer on and in tow haul and it would run forever unless it had to shift after the trans warmed up to ~160*.
Sticking valve caused by torque converter material.

Thanks for letting us know.

DEWFPO

I wish everyone updated their posts with solutions when found, but glad you got it fixed caveman!