First time poster, long time lurker. Trying to troubleshoot my Hummer H3 Alpha with aftermarket aluminum radiator and external transmission cooler. Replaced transmission 6 months ago due to dreaded strawberry milkshake mixing of trans fluid and antifreeze. At that point I decided to separate the trans cooler from radiator. The trans cooler I installed, which may be the problem, It is my first time doing this, which is probably obvious from my choice of cooler. It ran fine for 6 months of mainly city driving with a few 200 mile runs at highway speeds. Went on a trip from Dallas to Chicago and at about 800 miles in the fitting with single worm clamp popped off the hose barb and drained all fluid within a few minutes. I managed to pull off immediately to minimize trans damage, got a tow and a shop replaced a part of the hose that was, according to them, a bad connection. They ran two new hoses to the external cooler, eliminating any splices and I was off and running again..no damage to trans. Then about 300 miles later, it happened again. same hose popped off where the single worm drive clamp was. Another tow and another shop flushed system, tested pressure in the line and said it was within specs. They added an additional worm clamp, so two total and thought that would work. 20 miles down the road (highway speeds) from there and again, it pops off. Towed back to same shop and all they can say is I should go back to stock radiator and use integrated cooler. Would rather not do that.

So current status is there has been no noticeable trans damage from this, shifts and drives fine and of course I don't trust the setup as it is. So I am asking for any thoughts/advice on what may be causing the problem...could it be as simple as just using a crappy cooler? I don't understand why it lasted so long and now fails more quickly so I am curious about transmission pressure in general. I have read through the posts here about external coolers and people seem to have great success with it so I want to work it out but could there be something else going on causing this?

Appreciate any feedback. Thanks!

 

Welcome to Hummer Forum! Couple of things come to mind:

1. When you first installed the hoses onto the cooler, I'm guessing the hoses and the cooler itself were dry (not coated with fluid), which is why the setup lasted the longest at first (~800 miles). Now that it has popped off multiple times, I'd be willing to bet the fitting is much more coated with transmission fluid (slicker). I'm thinking this is making it easier to slide the hose on/off, which is exacerbating your problem (going from ~800 miles, now to ~20 miles before the fitting pops off).

2. How big is the rubber hose in comparison to the metal fitting on the transmission cooler? In a perfect world, the hose should be fairly snug as it is without any clamps installed (takes a small amount of resistance to push the hose on/pull it off the cooler). If the inner diameter of the rubber hose you're using is significantly larger than the transmission cooler fitting, and you're relying on the hose clamp to tighten/hold the hose in place, then you're likely not getting enough clamping pressure on the transmission cooler fitting itself, and I would consider changing the hose size and using something a little more snug.

3. How tight are you tightening the worm gear clamps? If you are simply tightening with a screwdriver and calling it good I would try tightening with a socket & ratchet instead (you'd be surprised how much more clamping force you can get this way). That said, at the same time, be careful not to over-tighten or you could risk damaging the hose, or worst case strip out the worm clamp gear; if you strip out the gear, get a new clamp immediately.

4. Not all worm gear clamps are created equal: lot of info out there online about which brands are better than others, but I'd consider buying ones that are higher quality than what came with your cooler. In most cases, I would say just find something that works, but if your vehicle has a history of the fittings coming off, especially for something as critical as a transmission cooler, I'd recommend finding something higher quality. I definitely would recommend 2x clamps per hose fitting (4x total).

Let us know what happens; hopefully it's something relatively simple.

 

Thanks for the feedback! The hose was very hard to get on there so it was tight without a clamp, and yes it was dry so good point on that. Do you happen to know how much pressure is supposed to be there? Could there be something else causing excessive pressure?

 

I am looking at getting a stacked plate cooler for this. Derale Hyper-Cool Extreme Remote Fluid Cooler with fan looks good but have not heard anything about them. The tru-cool seems to be a good choice as well. I live in Dallas area so it does get hot in summer.

 

I couldn't tell you the exact amount of pressure needed, but I would at a minimum get high quality hose clamps and tighten with a socket/ratchet. I normally bias towards not over-tightening, but in your case I would take the risk and tighten more than usual (tighten to what you normally would, then go even a little further). If you strip out one of the clamps, then throw it away and put another one on.

If you tighten them with a ratchet, and the hoses still end up coming off, then I am honestly not sure what would be causing the problem.

If you do end up looking at another transmission cooler, since you're bypassing the stock cooler, and you live in a hot climate, make sure the cooler you get has enough cooling power in and by itself to cool your transmission; some coolers (the smaller/cheaper ones) are designed to be installed inline with the stock (radiator) cooler and only provide "additional" cooling. Installing this type of cooler by itself would (in theory) provide less cooling power than if you only had the stock radiator cooler installed.

20,000-40,000 BTUs is the recommended amount for most heavy duty trucks; since you live in a hot climate, I would bias more towards the 30,000+ range. The Derale Hyper-Cool Extreme Remote Fluid Cooler certainly looks like it would meet that requirement. The AN fittings will definitely help prevent the hose lines from popping off as well.

 

Perfect. Thanks for the advice. I will get a new cooler and report back here with results.

 

Oh a bit more info on my situation. I failed to mention from the start that I used a Superchips Flashpaq F5 to allow for my 35's and hopefully get better gas mileage. I tuned to the gas saving setting 2 tanks of gas before the trip where the problem started in city with no problems. Not sure if this info matters or not. Should I go back to stock tune?

 

You were lucky to get what you did out of it before the hose demons reared their ugly head. Worm gear clamps suck for that application and the hose barbs on your cooler suck for that application. In marine applications, a long barb is always double clamped, each going the opposite direction. Upgrade your clamps to something designed for pressurized transmission hoses that have a full band.

Like these at a minimum.


I did my T Cooler with SS Braided Hose and 6AN threaded connections, never going to fail at any time.


You hand held tuner changes are not related to your hose failure caused by low budget connections.

 

Thanks doc! nice setup...going to do the same here with new cooler.

 

Replaced crappy cooler with remote cooler from Derale: Details here
On the trans lines close to the radiator I replaced the hose barb part on the hard line with a compression fitting to 6an. 6an hose to cooler with same connection. No more clamps and going strong. Thanks for all the help!