2006 Duramax LBZ Sierra HD 2500 Pickup trans cooler hose leaks.

A lesson in KISS? You decide.

I couldn’t ignore it any longer those Leaking Trans Cooler hoses were leaving tracks under my 2006 Sierra.  This is a typical problem, but how to fix it right at least cost, how to ignore the hype of costly after market fixes?

Climbing up under the front, I noticed that the front frame rail passenger side was bare shiny metal, not a bit of rust, although the leak was small, it stripped a bit of paint over time.

If you haven’t looked, the stock trans cooler hoses are made up with pipes and fasteners at each end, the pipes (tubing) have a hose barb that slips inside the 5/8 ID hose, and then a piece of metal is crimped in place over a lip at the beginning of the hose barb, and towards the head of the barb.

stock hose crimps





Above: Here’s one of the stock hoses removed, the crimped on sleeves cut off over the tops of the hose barbs, and pried off

Step one of any fix is research, and of course there’s multiple ways to fix anything right.  But my approach is to do it KISS, and what’s simple has everything to do with your skills and the tools you have on hand.

But first we read the stories of people who went to the dealer for the fix, $500 for new factory hoses installed and they failed again at just over a year later according to some testaments online.

What causes the failure you ask?

I think it’s a materials issue, I’m not sure the hose is held in enough compression to resist leaking at below freezing temperatures, there’s way too many reports of leaks discovered when it is freezing and below. But once it does leak, it‘s possible that the outside of the hose degrades with ATF exposure, it may get spongy and the connection then leaks at above freezing temperatures? I think that is likely the case, but I’m not sure.

Now.. I’ve heard the Dealer knows the old assemblies are a problem, but will that stop them from putting another old one on your truck? I don’t know, one guy said he’s had three sets of bad ones. That’s about $1500 worth?

I invested some time to study after market fixes, some are very expensive at $350 plus for the hoses and ends, and then you do the work. This more expensive solution causes you to cut off the hoses and hose barbs, I’m not sure I like this solution since it costs more money, and you have a slight chance of contaminating the inside of the pipe with a metal burr?  Is that the smart way? Do you really need 3000 PSI hoses and fittings like some offer, and for big money?

I made a trip down to NAPA, what a disappointment, the guy offered me some heater hose, I then went to a second automotive place, and the guy said he could only look up by year make and model… are you kidding me?

Time to get serious, so I go to a place in the Kent Valley called American Hose. http://www.americanhose.com/inventory/index.php

With the help of the knowledgeable counter man, I chose a parker hose branded with these markings: Parker 801-10 WP 2, 1 MPA 300 psi  5/8 1407251736

Yes, even 300 PSI is overkill, but this hose is rated for fuel the man says.., so ATF likely no problem. This is $3.50 a foot, way better price than other stuff people use at $15 and more a foot.  And a quality band type fastener is all you need.

In my case, the first hose I replaced was two clamps at $4 each, and 8 1/8 inches of hose. I’ll watch this hose for a bit, the counter man says no need for constant tension clamps, but I got them if I see a weep anywhere.

Now we get to the KISS part, I had a die grinder ready, with a composite blade mounted, I have a steady hand, and enough experience to keep it steady so not nick the radiator hose. You’ll need this or similar to cut off the crimp, and to make absolutely sure you don’t crush, bend or nick the tube with the composite blade. You need carefully insert a screw driver into the slot you cut, and expand it till you can peel it all back, and break that last tiny bit by the lip at the beginning of the hose barb. Once this is cut off, it’s all easy to fit back together.

Here's the old and the new for your compare

Here’s the old and the new for your compare




Above: The new hose is blue, old hose has the crimped on pipes, and at this joint they leak, first at low temps, and later at any temp according to many.

But maybe you ask, what were the marking on the hose that failed? Here’s all the markings on mine: 502U5F-1 CM, RY, CM 5/8 ID GM626OM DF

Some notes on this fix, there’s a plastic skid pan under my truck that comes off quickly with 15mm socket, this gives plenty of access to cut off the crimps, and do your work under the truck on a creeper, no need to remove pipe ends, just be ready to drain out the ATF in a catch when you remove the stock hoses, plan for about a half pint per hose.

Having read this post might save you a hundred dollars..

George B.

PS, I bet you thought I’d never post again…..




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25 Responses to 2006 Duramax LBZ Sierra HD 2500 Pickup trans cooler hose leaks.

  1. Happy New Year George!
    What a great writeup! I’m especially glad you included the part about sourcing a hose locally… How frustrating it is when the counter person is trained to lookup something by application and the specific job does not.

    There are a few of these trucks around this neck of the woods and I suspect they are not immune to the leaking hose!


    PS – Glad you’re posting again!!!!!!!

    • George B. says:

      Hello Jerry! Always a pleasure to hear from you. It’s funny what we DIYers think of. I am waiting for another cold morning to visit a mall parking lot. To spot trucks, and look for fresh red drips from under the front. It reminds me of a day when I was found in the bottom of a dumpster, a man scolded me and later found out I had permission from his boss. I was searching for the perfect donor part to machine and I found it that day!

  2. Eliot says:

    Happy new year George and the rest of the trade of DIY.


  3. sw lee says:

    Happy New Year George,

    Greeting from the far east tropic.

    Glad to read your posting again.

    • George B. says:

      Lee, it’s always a pleasure to hear from you! You have taught me things your Father taught you. And when we trace that source of knowledge; it goes all the way back to your father as a boy being given that first diesel tractor to drive; the one that no one else wanted. For those that don’t frequent this haunt, our DIYer clan is spread around the world. We need understand where our knowledge comes from; and that said.. ‘many thanks to you’.

  4. Russ D. says:

    Nice write up George.

    Reminds me of what I went thru replacing remote oil filter hoses on a 4×4 S10.
    Same symptoms, leak when cold then leak all the time. Same results at the parts houses, then went to a local place that made up hydraulic hoses and got the supplies.

    It’s disappointing that the percentage of people who work at auto parts stores who actually DIY is dwindling. Too many ‘gotta have the year, make and model’ types.

    I’m thinking more and more the nomenclature of ‘McParts’ is getting to be a proper term.

    BTW, glad you’re posting again.


    • George B. says:

      Russ, I think value engineering is a necessary thing, but if I had to take a wild guess, I’d say the vendor chose a hose with a liner capable of tolerating the ATF, and it was a cost saving over a hose that was fully constructed to tolerate petrol products. It’s almost always a ‘follow the money thing’. I think this is where ‘just in time’ purchases make since in the Auto manufacturing world. In the best model, the part is bought just minutes before it’s put on the Auto, when there’s a defect, a manufacturer ‘could’ force quick corrections to be made. But now days, the Auto manufacturer has Gods to please before they worry about pleasing the consumer.

  5. Robert Ruggiero says:

    Nice write up,only thought screw hose clamps have the tendency to not have equal pressure it will be a tad loose at the worm screw.May never be an issue in this application but I have seen slow leaks because of this.

    • George B. says:

      Robert, you’re a good tech, with a good observation. The clamp I used has a thin stainless sleeve that attempts to equalize the compression. I found a constant tension clamp on line that was initially used for heater hoses, these can be had for a price of 4 for $10 delivered. The Counterman said the combo of the hose and ‘quality’ clamps don’t cause problems. This is the ‘Go To’ shop in valley which is full of hydraulics, and every sort of industrial application. If I have even a weep of ATF, I’ll add to the comments here. No doubt GM used similar hose assemblies elsewhere, and we DIYers need understand how to fix it right for the least money and effort.

  6. Quinn says:

    Happy New Year, George. It’s tough when there doesn’t seem to be anyone who knows the clear answer to the leak problem. And I share your frustration with the dearth of hands-on experience behind the parts counter. But that’s what DIY is all about. Hope your fix keeps the oil where it’s supposed to be.

    • George B. says:

      Quinn, here we might note, it is a trait of the DIYer to want to know, it’s what we think life is all about? Continued learning, for us life will never be boring.

      Are we really one percenters? It is times like when I’m in front of the counter that I think our numbers could be that low.

  7. Joeelectro says:

    Hi George-
    Glad to see you posting again. We miss your insights and also the rants!
    Nice hack on the transmission lines. A better and simpler repair for far less money than new hoses….
    Any chance of the PMG going back into production?

    • George B. says:

      Thanks Joe, I should write a book on the PMG, I have years invested, and years more of thought after production. I don’t think I’m up for it, the PMG is the Gen Mad Max would want, but it’s best at 3KW and below.

  8. russ says:

    Welcome back

  9. JackG says:

    Happy New Year George and all Happy DIY’ers

  10. Claude Lamarre says:

    Hello George. This is my first post ever, anywhere on the net, I am happy to wish you a happy new year and thankful I got your CD a while back (treasure of info for DIY )
    Iwas getting kind of worried (jan 25 2015) I love to read your KISS analysis/solution to whatever strikes your fancy (pushes your button ? ) I read your student/scientist/pragmatist/realist (to my view) analysis of what the situation is and possible solutions which help me strive to be a better DIY by keeping an open mind and
    remembering I will never know it all ! .So l’ets keep learning. thank YOU for the inspiration George. Claude L.

  11. Craig Hooper says:

    The world has seem to go over to a box part fix mentality nobody sells the pieces to fix the part everyone just wants to sell you the whole unit to replace it reminds me of when I was working for a major trucking company I had backed into a dock on the way into the office I noticed a drip trail thought hope thats not me well it was I called the company maintenance department and they want to tow me 120 miles to their company shop and I told them was just a little hole from the hose rubbing on The end of a breather tube it wouldn’t be hard to fix it took a little bit of arguing because nobody thinks the driver knows anything but they finnally gave me of the name of a shop in the little town I was in and I took it over there and told them what was wrong and they didn’t believe me either because for some reason everybody thinks the truck drivers are idiots but I really lucked out because the shop had a press to do hydraulic fittings so he cut it at the hole and put a fitting of each and and then coupler between the two it was fixed alot better than it would have been as the metal fttings he put on we’re now at the wear point.
    I have always wondered how much I saved myself on this one my big concern was downtime as I knew it would probably take a day and a half for the shop to even look at it once they towed it there so there’s probably two days that I wouldn’t of gotten any work at least

    And then there’s that Mechanics bill I know I saved them alot on parts I still remember the bill because the transmission fluid was so expensive I couldn’t believe it $35 on fittings $120 on labor and something like $563 in transmission fluid it was like $35 a pint But to get a semi in and out of the shop for under 1000 is quite a feat

    • George B. says:

      I know nothing about rolling shops on wheels, but it does seem like trucker/mechanics might make more money getting trucks back on the road than driving them, and as far as $35 a pint goes, the best synthetics are less than $5 at Wal Mart, calling Uber to take you there and back might be an option 🙂 Craig, I always appreciate your input, you’ve shared some valuable info, and saved me some money in the past..

  12. Randall says:

    Good to see your still there George.
    I had feared the worst…the wild fires of last year.
    Thanks for all your contributions.


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