The Dreaded H3 Tranny Cooler / Radiator Issue

[Bigunit]

This past Friday, Cotilo's '08 H3 Lux rig had the the tranny cooler inside the radiator give out. If/when this happens, you will get anti-freeze in your tranny and the tranny will be fried real fast. If the repair is not covered by warranty (B & B or the GM extended premier plan) you are looking at a new radiator, hoses, seals, gaskets & transmission needing to be replaced at an estimated cost of $2,000-4,500 - and possibly needing a new engine if the antifreeze got sucked into the engine and damaged the engine. She had it towed from her work to the GM dealer/HUMMER service facility

I'm not sure how you can catch this before it happens but if it does give out, you won't get any warning lights or codes and are looking at a major repair bill. Your tranny will start to slip and then quicky after that, the tranny will give out. Cotilo's '08 H3 Lux only has 55k mi. - has been dealer serviced from day 1 with all factory scheduled maintenance. The GM regional rep is coming to town tomorrow to assess and confirm the damage. Glad she had the GM extended warranty with $100 deductible. So far, the tranny and radiator need to be replaced. Waiting to see what they say about the engine.

 

[3Hummers]

Ouch. 85K on the 08 Alpha and no issue like that. B2B expires at 95K.

 

[alrock]

Glad you caught it before she drove it too far. Ironic that the pavement princess H3 has this issue but the off road H3s have been fine.

 

[amrg]

Is there a proper way to avoid this for those people already out of warranty?

 

[Scarsman]

Bypassing it and installing an aftermarket tranny cooler is your safest route. Plus you get better cooling for both your tranny and your engine.

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[ReconH3]

Bypassing it and installing an aftermarket tranny cooler is your safest route. Plus you get better cooling for both your tranny and your engine.

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That's how I have it. I don't use the factory radiator for the tranny fluid at all.


"Ex Umbris Venimus"

 

[06 H3]

Sorry to hear that BU, luckily you have the warranty!

Recon do you have a write up on it? I wanna avoid this lol

 

[Expendable]

Never knew the H3 has a problem with a cooler similar to the H1's Vampire problem.

 

[MaxPF]

Is there a proper way to avoid this for those people already out of warranty?

This is 100% guaranteed to avoid this and other auto trans problems:

If you must have the slushbox, then go with what Scarsman said: put an external cooler on and do not use the in-radiator cooler at all.

Another option is to prophylactically replace the radiator....

 

[amrg]

Im interested if there is any thread showing how someone has done this. Perhaps I can get to do it once Im out of warranty.

 

[soct]

Does anyone make a solid aluminum radiator. I would like to replace the plastic hybrid piece before it goes out.

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[cbetts]

I never understood the concept of putting engine heat back into the tranny. Best to just do what MaxPF said and ditch the built-in tranny cooler and only run an external cooler.

 

[ArtHummer]

So, from reading the symptoms... If the transmission is slipping. First turn off the engine and check the level of antifreeze. If the level is low and you see some oil contaminates, then you are screwed. Call the tow truck.

 

[alrock]

I believe Bebe has an external trans cooler, kflips might and TheBroken did as well.

Ron Davis makes a drop in solid aluminum radiator for the H3, but it does have the integrated trans cooler. Hmm, since Bebe runs this she may not have an external trans cooler right now, I'm not sure.

 

[Schwarttzy]

Man I think I'm going to replace my radiator for a solid aluminum one sooner than I thought after reading that, but wow that Ron Davis website sucks.

 

[chaos254]

What external cooler is everyone running? Anyone have a write up for doing this? After reading this I want to get this done soon because I definitely can't afford that kind of issue

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[MaxPF]

I never understood the concept of putting engine heat back into the tranny. Best to just do what MaxPF said and ditch the built-in tranny cooler and only run an external cooler.

The idea is to rapidly warm up the trans fluid and hold it at a stable temperature. The problem is that modern engines run hot for emissions reasons, so your minimum trans fluid temp without an external cooler is going to be your engine temp - temp drop across the radiator (usually around 10 degrees), so figure 200 degrees. This is awful hot for ATF - 160-180 is much better. External coolers add cost, and manufacturers love cost-cutting, so unless the vehicle will cause excessive trans warranty issues without an external cooler the OE is not going to include one.

A good example of GM's cost-cutting is the ZF 6 speed transmission used behind Duramax trucks (until they discontinued it - the Allison ought to be good enough for everyone, right? :hjob. ZF designed the transmission with an internal oil pump which circulates the fluid through an external cooler (OD operation in any transmission generates a lot of heat), and both GM and Ford used the ZF 6 in their diesel trucks. Ford used the pump and external cooler, while GM cheaped out, eliminated the external cooler loop, and specified synthetic lube instead. Want to guess which manufacturer has heat-related ZF trans problems when their trucks are used at or near max GCWR?

 

[ALPHA of JONESY]

Man I think I'm going to replace my radiator for a solid aluminum one sooner than I thought after reading that, but wow that Ron Davis website sucks.

You got that right. I email them some time ago and they quoted me around $1000 for the H3 Radiator. OUCH

 

[soct]

Anyone else make one. A thousand for a radiator is a lot more then I want to spend. Also I would like to see write up on a trans cooler as well.

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[MuDnYrI]

I installed the Tru-Cool MAX transmission Cooler.
Here is the Part number 4739-1 and does NOT include the external thermal bypass for colder climates.
This is the Cooler that most people replace with. I did this Mod a few years ago. Best $150. I ever spent!

 

[06 H3]

The idea is to rapidly warm up the trans fluid and hold it at a stable temperature. The problem is that modern engines run hot for emissions reasons, so your minimum trans fluid temp without an external cooler is going to be your engine temp - temp drop across the radiator (usually around 10 degrees), so figure 200 degrees. This is awful hot for ATF - 160-180 is much better. External coolers add cost, and manufacturers love cost-cutting, so unless the vehicle will cause excessive trans warranty issues without an external cooler the OE is not going to include one.

you think heat is a major contributor to trans failing at an early life compared to other trans? Mine runs 220+ in the summer.

 

[MaxPF]

You got that right. I email them some time ago and they quoted me around $1000 for the H3 Radiator. OUCH

And you will be lucky if it lasts 4 years. Neither of Todd's RD radiators made it that long

Seriously, stick with the stock type radiator.

you think heat is a major contributor to trans failing at an early life compared to other trans? Mine runs 220+ in the summer.

Yup. 220 is way too hot for a prolonged period. Get yourself a good external cooler. Also, lose the crappy Dex VI and put in an Allison TES-295 spec fluid (Transynd, Mobil Delvac Synthetic ATF (NOT MOBIL 1!!!!)).

 

[06 H3]

That's nothing maxPF! Lol climbing hills I would go up to 240 in the summer and had to stop to let it get back down to its "normal" 220. I have 103k on my original trans. I'm sure it's at the end of its life...

 

[alrock]

I'm not too worried about trans #2 in my truck. It's got a 100K warranty and Greg, you'll probably be putting in a 4L80E eventually anyway.

 

[MaxPF]

That's nothing maxPF! Lol climbing hills I would go up to 240 in the summer and had to stop to let it get back down to its "normal" 220. I have 103k on my original trans. I'm sure it's at the end of its life...

Maybe. Again, good fluids make a big difference. A lot of heat-related issues are breakdown of the fluid and it's add-pack.

I'm not too worried about trans #2 in my truck. It's got a 100K warranty and Greg, you'll probably be putting in a 4L80E eventually anyway.

You won't be putting a 4L80E behind the I5.