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Radiator (internal) transmission cooler bypass?

DFW Spartan

Well-Known Member
Messages
125
Location
Dallas, TX
So one of the first things I was told to do when I bought my T was to install an external transmission cooler, and bypass the internal one in the radiator, due to it commonly failing and taking out the transmission in the process. So it’s been two years now, and I still haven’t gotten around to it. However, after recently reading about several H3/H3T owners with relatively low miles (80K) having their internal transmission coolers recently fail, it’s back on my radar.

On one of the social media H3 groups, a member indicated that most of the trans cooler failures were with the original radiators that came in our trucks (quality issue GM didn’t own up to and issue a recall for), and that later OEM radiators don’t seem to exhibit that same issue. Does anyone know if there’s any truth to that? Multiple automobile manufactures run trans coolers in the radiator (liquid more efficient cooling agent than air), and in fact most manufactures of external trans coolers recommend that you run them in parallel with the internal cooler. I’m just wondering why you hear about the H3/H3T failing so often.

For you folks running aluminum CSF radiators, are you utilizing the internal transmission cooler as designed, or are you also bypassing it with an external trans cooler? I haven’t heard of an aluminum CSF radiator failing for this, but I guess that could be because there are less of them in service.

When I took ownership of my T at 63K miles, the radiator looked relatively new. However I doubt the original owner would have already replaced the radiator at that mileage. I’m currently at 74K miles, and want to get out ahead of anything catastrophic. I’m debating on whether to 1) buy a new OEM radiator for a manual transmission (no internal trans cooler, more radiator cooling surface) and adding an external cooler with thermal bypass, 2) buying a new OEM radiator and running an external trans cooler in parallel with the internal cooler (under the assumption that it was a quality control issue with the original radiator), or 3) buying a CSF radiator and running an external trans cooler in parallel with the internal trans cooler.

There’s something to be said for peace of mind though. For you folks that are running an external trans cooler and bypassing the one in the radiator, any issues with your current set-ups?

Thank you in advance for any and all feedback.
 

Bowser-II

Well-Known Member
Messages
268
Location
Hagerstown, Maryland
The radiator can crack at any moment, just bypass for now and replace it only when necessary.

I run a larger radiator for towing and swapped out for a manual radiator.





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Alpha X

Well-Known Member
Messages
409
Location
The Motor City
My internal cooler failed a few months ago. It was a new AC Delco radiator I had purchased from a Chevy dealer that failed. It was only a few months old. I haven’t posted much about my experience, but I was going to put together a thread. Long story short I installed another new radiator from a H3 manual transmission truck, which does not have an internal cooler. I flushed the trans really well. Flushed the engine really well. Installed a Hayden 676 external trans cooler in the upper passenger side area in front of the radiator. The trans has been working fine so far. I would encourage everyone to bypass the internal cooler so the $250 rad doesn’t ruin a $2500 trans.
 
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Dana60H3

Active Member
Messages
43
Location
San Bernardino CA
In my 2008 Alpha I have ran the CSF radiator for the last year and use the internal cooler. I haven’t had any problems with it. Done some good wheeling with it and haven’t had any issue with cracking or leaking.


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alrock

El Diablo
Staff member
Messages
10,442
Location
Scottsdale
I have option #1 (OEM manual trans, full bypass) and I've had no cooling issues here in AZ even with our heat, but I admit I do not have a temp gauge on the transmission. Current transmission has about 63,000 miles on it and fluid has been changed once or twice and has not exhibited any issues. If you go this route, remember to upsize the external cooler to make up for the loss of the internal cooler.

I don't the the internal trans cooler failures are frequent by any means but it's just that the consequences can be so catastrophic. Like you said, it may be for more for peace of mind than actual necessity.
 

EndeavoredH3

Well-Known Member
Messages
371
Location
Arizona
My setup for the transmission cooler runs in series with the OEM cooler in the Radiator. I did this because of the cold temps we see in the winter here in Flagstaff, Arizona.

I tested my setup mid July in 110 degree heat (it’s a dry heat) and ran it up and down the I-17 at the heat of the day and never rose above 200 F.

But since Arizona decided to only have one week of fall and immediately go into winter, my setup is currently biting me in the ass. The transmission temp will not rise above ~120 F. So I will need to add a 180F bypass so that the fluid rises up to operating temperature.

I have pics and part numbers if your interested.
 

txpetroguy

Member
Messages
7
Location
DFW
I just installed a Derale 13613 Series cooler with a 25792 Fluid Control Thermostat bypassing the factory radiator cooler. The thermostat fully opens at 180 but so far the transmission hasn't gotten over 162. At highway speeds, my water temp stays at 178-182 while the trans is at 162. During my morning drive at 40 degrees, the engine reached it's operating temp in about 5 mins of stop and go driving where as the trans took about 10 minutes to reach 160. I'll have to wait until Texas decides to warm back up to see how it cools in the heat.
 

DFW Spartan

Well-Known Member
Messages
125
Location
Dallas, TX
I appreciate the feedback. I ended up doing quite a bit of reading last weekend and came across several of your threads on the topic in the Tech and Build sections. While I’d like a CSF all-aluminum radiator, I also need new tires next month, so a $500 radiator isn’t in the cards right now. So for the time being, it looks like I’ll be adding an external trans cooler and bypassing the OEM radiator. I live in Texas, but make snowboarding trips to both Colorado and New Mexico, so I’ll be adding a thermal (low temperature) bypass. I purchased a transmission filter and gasket, and will be dropping the pan when I install the new cooler. I also ordered an OBDLink MX OBD-II adaptor last weekend, so I can start monitoring engine performance and temps. If I end up needing more cooling, I’ll pony up and buy a CSF aluminum radiator later when I have more funds, and run the external trans cooler in parallel.

I’ve noticed some manufacturers rate their coolers by GVW and some by BTU, which makes it little more difficult to get an apples to apples comparison of size to cooling efficiency. Most trans coolers, with the exception of the Tru-Cool Max, are designed and rated to run in parallel with the existing trans cooler. Because I’m bypassing the trans cooler in the radiator, and air doesn’t cool transmission fluid as efficiently as the fluid in the radiator, I’ll need to go with a larger trans cooler. So I guess that’s where I’m at now, trying to figure out how much cooling capacity I need, how much space I have to fit it in, and which cooler will fill that footprint most efficiently.

I’m currently running 35’s. I’ve installed Rocky Road Sliders, a Gobi Stealth Rack, and a new brush guard. In the future, I plan on adding more weight in the form of a winch and UCP. Weekends, I’m usually loaded up with recovery gear, camping equipment, mountain biking gear, etc. Considering all the extra weight, how large (GVW and/or BTU rating) of a cooler would you recommend I go with? I’m currently looking at units from Derale, Hayden, Tru-Cool and B&M. I haven’t had a chance to pull the grill yet to see how much space I have and mounting options. I hope to get to that this weekend or next.
 

alrock

El Diablo
Staff member
Messages
10,442
Location
Scottsdale
This is the one that I installed, which was essentially a couple of steps larger than the recommended inline cooler. Long Tru-Cool LPD Automatic Transmission Oil Cooler 4589 24,000 GVW. Note that I've essentially got the same build as you with a winch bumper installed. Reloader likely undersized his first cooler so he bought a second one of the same, stacked them, and ran them in series to get his cooling.

Please be sure to look at videos and instructions on how to mount this properly for best cooling. In short, you don't want air pockets so you have to pick inlet and outlet carefully. A used H3 I looked at a while ago had a trans cooler bypassing the radiator and it was incorrectly installed and would thus be less efficient.

It sounds like you've done some good research and have a good plan in hand.

On a side note, if your radiator hasn't failed, and you are being careful with funds, why even go the length of replacing the radiator at this time? Bypass the radiator, put caps on the radiator trans fittings (do not loosen or remove those fittings!) and let it be. If you like the CSF don't spend $100 or $200 on another radiator now. Keep the $ in the bank until you pull the trigger on what you want. I ran the same radiator for several years until I stumbled across a deal for OEM radiator w/o the trans cooler.
 

JPaul

Well-Known Member
Messages
2,400
Location
Way up north, UT
Pretty sure that's the same cooler I used. I bypassed my internal cooler as well. Fully loaded and towing a trailer the temps never have gotten above 200F. Driving around town they stay around 180F max, usually more toward 140-160F.

I didn't put a bypass in yet but even with cold weather it does OK with not getting too cold.

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DFW Spartan

Well-Known Member
Messages
125
Location
Dallas, TX
alrock and JPaul – I appreciate your inputs. Knowing this unit handles the transmision cooling requirements of our rigs, with all the additional weight we’ve got bolted on and can handle towing, is great. It takes the guess work out of the equation. Thank you.

Since my original post, I forgot mention that I decided not to replace the current radiator, just bypass the internal trans cooler for the external one. If/when it fails in the future, I’ll decide what to replace it with at that time. I plan on blowing any residual trans fluid out of the old cooler with low pressure air, and plugging the inlet/outlets like Firesquirt did in his write-up. Alrock, I went back and read your “Transmission Cooler Thread Number 3 – install with pictures” thread in the Tech section. Per your recommendation, I’ll be removing the crimps and rubber hoses from the trans lines, and connecting the new lines from the external cooler directly to the existing trans lines with factory barbs, thereby eliminating another known weak/leak point.

With regards to mounting direction of the trans cooler, a couple manufacturers indicate that their coolers can be mounted in any direction, and there are many folks on the inter-web with trans cooler how-to installation instructions doing just that. However, my understanding is that there are only two efficient ways to mount a trans cooler. Method 1 - Vertically, with the inlet (hot line coming from the transmission) at the bottom, and outlet (cool - return line going back to the transmission) at the top. Method 2 - Horizontally, with the inlet/outlet lines to be facing upwards, so the fluid fills the entire cooler before being pushed out the return line. Is that correct, or is my understanding off?
 

DFW Spartan

Well-Known Member
Messages
125
Location
Dallas, TX
I just installed a Derale 13613 Series cooler with a 25792 Fluid Control Thermostat bypassing the factory radiator cooler. The thermostat fully opens at 180 but so far the transmission hasn't gotten over 162. At highway speeds, my water temp stays at 178-182 while the trans is at 162. During my morning drive at 40 degrees, the engine reached it's operating temp in about 5 mins of stop and go driving where as the trans took about 10 minutes to reach 160. I'll have to wait until Texas decides to warm back up to see how it cools in the heat.

I was originally looking at the Derale 13613 or 13403 (10000 Series). Any chance to you have pics of your install?
 

DFW Spartan

Well-Known Member
Messages
125
Location
Dallas, TX
My setup for the transmission cooler runs in series with the OEM cooler in the Radiator. I did this because of the cold temps we see in the winter here in Flagstaff, Arizona.

I tested my setup mid July in 110 degree heat (it’s a dry heat) and ran it up and down the I-17 at the heat of the day and never rose above 200 F.

But since Arizona decided to only have one week of fall and immediately go into winter, my setup is currently biting me in the ass. The transmission temp will not rise above ~120 F. So I will need to add a 180F bypass so that the fluid rises up to operating temperature.

I have pics and part numbers if your interested.

Endeavored - Can you forward me part numbers and pics of your install?
 

alrock

El Diablo
Staff member
Messages
10,442
Location
Scottsdale
With regards to mounting direction of the trans cooler, a couple manufacturers indicate that their coolers can be mounted in any direction, and there are many folks on the inter-web with trans cooler how-to installation instructions doing just that. However, my understanding is that there are only two efficient ways to mount a trans cooler. Method 1 - Vertically, with the inlet (hot line coming from the transmission) at the bottom, and outlet (cool - return line going back to the transmission) at the top. Method 2 - Horizontally, with the inlet/outlet lines to be facing upwards, so the fluid fills the entire cooler before being pushed out the return line. Is that correct, or is my understanding off?
I agree with the sites that recommend these two mounting methods. I used method 1.
 

DFW Spartan

Well-Known Member
Messages
125
Location
Dallas, TX
This is the one that I installed, which was essentially a couple of steps larger than the recommended inline cooler. Long Tru-Cool LPD Automatic Transmission Oil Cooler 4589 24,000 GVW. Note that I've essentially got the same build as you with a winch bumper installed. Reloader likely undersized his first cooler so he bought a second one of the same, stacked them, and ran them in series to get his cooling.

Went ahead and ordered the Long Tru-Cool LPD 4589 trans cooler, and Derale 13011 thermostat today. Thanks for yawl's inputs.

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EndeavoredH3

Well-Known Member
Messages
371
Location
Arizona
Endeavored - Can you forward me part numbers and pics of your install?

Sorry for the semi-late response, hectic week/weekend. The part number for the cooler is LNG-4454, it is a long Tru-cool cooler and is rated for 18000 GVW. For me everything included in the kit was good enough for the install besides buying some more hose at autozone. Below are my install pics. For how I ran the cooler(Transmission Outlet Line -> OEM rad cooler inlet -> OEM rad cooler outlet -> Bottom inlet of Aux cooler -> Upper Outlet of Aux cooler -> Transmission Return line). I know that you're aiming for eliminating the radiator trans cooler but all information is useful information :horns:. Scanguage picture shows the hottest temp I achieved while towing a small fisherman boat up the I-17.



IMG_8787 copy.jpgIMG_8788 copy.jpgIMG_8794 copy.jpg

In the Photo below, on the "to trans" line I cut off the barb on each side and flared each end. (Alrock opened the crimp on the hose and used the factory flared ends). So from the OEM cooler it runs to the aux cooler and then the aux cooler to the transmission.

IMG_8781.jpg

 

Alpha X

Well-Known Member
Messages
409
Location
The Motor City
When cutting the crimp off the transmission lines, be careful. The crimped metal is maybe 1.0mm thick. If you cut too deep, you'll nick the trans line. You don't need to cut all the way through the rubber hose. It will pull off when the metal crimp is cut. I used a dremel tool with a small cutoff disc and it made pretty easy work of it. I'd post a picture but my photos are always too big to post here.
 

JPaul

Well-Known Member
Messages
2,400
Location
Way up north, UT
Yep, the crimped metal on the hoses is aluminum so no need to get carried away with cutting it. Even a pair of side cutters is sufficient.

I just came back from Colorado towing a couple thousand pounds worth of trailer and restaurant equipment along with my wife and 3 daughters and the back full of my fridge and recovery gear and our luggage, along with some other items my mom gave me. We took I70 back and anyone that has driven that knows it has plenty of steep passes to climb. Highest the transmission temperature got was maybe 205F. Granted it was fairly cool out, probably in the 60's, but that's still pretty good especially considering most of those climbs I was maintaining the speed limit of 65mph.

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DFW Spartan

Well-Known Member
Messages
125
Location
Dallas, TX
This is the one that I installed, which was essentially a couple of steps larger than the recommended inline cooler. Long Tru-Cool LPD Automatic Transmission Oil Cooler 4589 24,000 GVW. Note that I've essentially got the same build as you with a winch bumper installed. Reloader likely undersized his first cooler so he bought a second one of the same, stacked them, and ran them in series to get his cooling.

Please be sure to look at videos and instructions on how to mount this properly for best cooling. In short, you don't want air pockets so you have to pick inlet and outlet carefully. A used H3 I looked at a while ago had a trans cooler bypassing the radiator and it was incorrectly installed and would thus be less efficient.

It sounds like you've done some good research and have a good plan in hand.

On a side note, if your radiator hasn't failed, and you are being careful with funds, why even go the length of replacing the radiator at this time? Bypass the radiator, put caps on the radiator trans fittings (do not loosen or remove those fittings!) and let it be. If you like the CSF don't spend $100 or $200 on another radiator now. Keep the $ in the bank until you pull the trigger on what you want. I ran the same radiator for several years until I stumbled across a deal for OEM radiator w/o the trans cooler.

So I finally got around to installing the Long Tru-Cool 4589 LDP Auto Trans Cooler I bought, along with a Derale thermostat (#13011). I was of the understanding the ID of the stock trans lines is 3/8". Since the thermostat had 3/8" NPT ports, I ran all 3/8" ID trans hoses. I know the 4589 trans cooler fitting is 11/32", but I was advised that 1/32" difference in a low pressure transmission system shouldn't be an issue. Well, since the install, the inlet hose (from the trans --> thermostat --> trans cooler) has failed (split) me twice right before going into the trans cooler. The first time I chalked it up to a faulty hose. Now that it's happened a second time, I'm thinking that the 1/32" ID difference is an issue, and the pressure build up is causing the hose to split. I have my trans cooler installed with the inlet/outlet facing up to prevent air pockets. I used 3/8" x 3/8" 90 degree elbow hose barb fittings, designed for auto/transmission use, at the bends to prevent any sort of kinking in the lines. Unless I have a faulty trans cooler or thermostat, the 3/8" line to 11/32" trans cooler inlet/outlet ID size is the only thing I can think of that would be causing pressure build up, and the hose to split at that location. You guys running the Tru-Cool 4589 trans cooler, did you use 11/32" or 3/8" ID hose? I've attached a couple pictures of my setup for reference. Any feedback on what might be going on here would be appreciated. Note: Inlet to trans cooler from transmission is drivers side in the pic.

ac83f60a1ac4b64ce83b898faa878458.jpg

0900e6a92dc2454d0376a1933e4798a8.jpg


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Jeepwalker

Well-Known Member
Messages
857
Location
WI
The beauty of the factory system is it's simplicity. Now there are 3 additional points of weakness:

1) A lot of rubber hose that are prone to burst or leakage: Or maybe you plan to go back and bend steel lines with flaired or brazed ends when time permits. Seen a number of leaks in my day. Course most of those were older hoses.
2) A bypass that can fail (hopefully it fails 'open')
3) Airflow impediment.

Not cutting down your work or efforts, just pointing it out. I get what you're trying to achieve. Thanks for raising the awareness and sharing alternative ideas. If you don't run into overheating issues, that will be great. If your AC doesn't perform as well, try moving the cooler. In Dallas, you need the condenser to be able to reject heat as efficiently as possible. Just a little reduced condenser efficiency can have a big impact on your cooling. It's not linear. (I work in HVAC).
 
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alrock

El Diablo
Staff member
Messages
10,442
Location
Scottsdale
Looking back at my notes, the ID of the trans lines is 3/8 so I doubt that your hose size selection is the issue. Is there a chafing spot on the hoses where it may have split? Are the hoses that you are using transmission line hoses? Maybe another brand would do better. I'm guessing here, I don't have a good answer for you.
 

alrock

El Diablo
Staff member
Messages
10,442
Location
Scottsdale
The beauty of the factory system is it's simplicity. Now there are 3 additional points of weakness:

1) A lot of rubber hose that are prone to burst or leakage: Or maybe you plan to go back and bend steel lines with flaired or brazed ends when time permits. Seen a number of leaks in my day. Course most of those were older hoses.
2) A bypass that can fail (hopefully it fails 'open')
3) Airflow impediment.

Not cutting down your work or efforts, just pointing it out. I get what you're trying to achieve. Thanks for raising the awareness and sharing alternative ideas. If you don't run into overheating issues, that will be great. If your AC doesn't perform as well, try moving the cooler. In Dallas, you need the condenser to be able to reject heat as efficiently as possible. Just a little reduced condenser efficiency can have a big impact on your cooling. It's not linear. (I work in HVAC).
The main thing many owners are trying to achieve is to avoid the consequences of what happens if the trans cooler fails. If an external one fails, you lose trans fluid. If an internal one fails, you mix trans fluid and coolant and you lose your transmission. Unfortunately, it's happened to too many owners so it's not just a theoretical problem to avoid.

I do agree that mods beget other mods or failure points so each one has to be chosen carefully. When I chose my external trans cooler, I tried to oversize it to make up for the loss in efficiency in having it contained within the radiator. Granted, I didn't pull up careful calculations for this but it's been working well so far for several years and many miles.
 
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