Tranny cooler installation
 

Replacement transmission cooler:

If you?ve done any research on the forums you know the stock transmission cooling setup is less than ideal. The transmission fluid flows through the inside of the radiator and an external transmission cooler. Over time, the tubing in the radiator fails and transmission fluid mixes with coolant, and once it finds its way back to the tranny, kiss it goodbye. My plan was like many others: bypass the radiator completely and install a bigger, more efficient external cooler.

I bought my cooler from here. I got the one without the bypass since I live in Kalifornia and don?t have to deal with extreme cold: http://www.oregonperformancetransmis...Code=LNG-47391

There is really only one place the cooler can go and it is going to be a tight squeeze.

Re: Tranny cooler installation
 

Step 1: remove the old cooler. I unbolted it and the cut the lines with a tubing cutter. The line that runs to the driver?s side was cut far out on that end to reduce the amount of hose I would need for the new cooler:



To make my life easier, I removed the airbox tube between the throttle body and filter. I also removed the passenger side fender liner.

Re: Tranny cooler installation
 

Step 2: Break apart the line that runs inside the radiator. I had to use my sawzall because I couldn’t get the tubing cutter to spin due to space restrictions. The circles are for the black tube at the top and the silver tube at the bottom.



Here’s where I cut the lower one. Just turn it up to keep the fluid from running out:



The other end of the cut will run to the cooler. The black tranny line you see runs straight to the driver’s side of the stock cooler and was cut in Step 1:



No pictures of the cut at the top, but it should be straight forward. I connected the two radiator cuts together with some of the hose that came with the new cooler. This step is not really necessary, but others had done it and it provides a clean installation.

Re: Tranny cooler installation
 

Step 3: Prep the new cooler by installing the NPTxbarb fittings:



Next, route the tubing to the new cooler location. The tube on the passenger side came from the lower cut shown in Step 2 and the tube on the driver?s side is connected to the end of the tubing that was cut in Step 1:

Re: Tranny cooler installation
 

Step 4: Pop the cooler in place and secure it to the body. I had it pushed all the way over until it hit the mount for the power steering cooler. I used a sheet metal screw on the driver?s side because the cooler bracket fit flush, but I had to use one of the included straps on the passenger side:

Re: Tranny cooler installation
 

Step 5: Close the hood and realize it won?t close! :lame: The cooler had to slide over towards the driver?s side by ? an inch or so. So I had to ?trim? the ps cooler bracket (thank you Mr. Dremel) to make it work. Fortunately, I didn?t have to redrill the hole on the driver?s side ? the bracket has 3 holes so I just used the one on the left instead of the one in the middle. For the passenger side, I added another hole and tweaked the bracket (it is what was hitting the hood):





Lastly, run the engine (after putting the airbox back together) and check for leaks.

Re: Tranny cooler installation
 

Nice wright up...

Dude I warned in one of the recent threads the very issue you had. The hood not closing due to tight fit. Luckily I caught mine before things were bolted down. Sorry you didn't see it :(

For the power steering I just relocated the bottom mount (swung bottom towards driver side) and used a nut and bolt that came with the Trans cooler to secure it.

Re: Tranny cooler installation
 

I saw your post, but everything looked like it lined up perfectly. It wasn't off much so it was no big deal to fix. You can see where the hood was hitting if you look to the lower right of the last picture. Just above the bolt you'll see two small parallel scratches. It was really modifying the bracket that fixed it more than sliding the whole cooler towards the driver's side.

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I just ordered a Trans cooler from Flex-o-lite (4120) Overall dimensions of 7 1/2" x 20" x 3/4". It appears to be very close to the same dimensions as the Unit you are all using but it cost me $53 shipped from summit. Not as thick not as wide and not as tall... but I don't tow anything with my H2... I just dont want to have coolant mix with the trans fluid... I will install it this weekend and let you know if it works. I have noted my currant trans temps and will see if there is any difference.

New to the Forum by the way... just bought my 03 H2 this week... So far I love it!!! have been trolling around here to get some Ideas and came across the stock trans cooler issue. I work at a GM dealership and the Techs there never heard of that issue... but they are going to pass it along to their H2 customers.

Re: Tranny cooler installation
 

^that's a good point, anything aftermarket I'm sure will work better than the tiny radiator integrated cooler. IMO it would be much much easier to buy a little smaller of a cooler and not worry about moving brackets, drilling holes, hood clearance etc.

Re: Tranny cooler installation
 

Egan, what year is your H2? My '05 didn't ship from the factory with an external tranny cooler.

Also when I installed my cooler I removed the tranny lines from the radiator (you just remove a retaining clip and they come right out) instead of cutting them. I then plugged the holes in the radiator with brass plugs instead of joining the upper and lower cut connections with a hose. Even neater still.

Re: Tranny cooler installation
 

2005

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I got my Flex-O-lite 4120 Trans cooler installed today... Very easy to do but I must stress how important it is to Flare the lines that are going to the trans cooler. it is very easy to do and the Flare tool is only $10 at your local autozone. Also when you run your lines make sure that any line (rubber or metal) that touches anything metal... make sure that you cover it with something. I just cut open some 3/8 rubber line and put it over the line that comes in contact and chaffe against anything.

Trans temps after an hour of driving in city and highway are below what they were since I got the H2. This cooler is rated for 20,000 lbs GVRW the H2 weighs in at 8000 lbs give or take so that means with this cooler you could tow an additional 12k I do not plan on doing that so I think I am set. I will however get the bypass because here in Wisconsin we get some cold temps.

Here are the completed pics of the FAL 4120 that I got for $53 shipped from summit and comes with everything needed for the install. Minus the tube cutter and Flaring tool.

Re: Tranny cooler installation
 

looks good, nice work. I was waiting to see someone use the zips that go through the radator/condenser to secure the ext cooler.

Re: Tranny cooler installation
 

I will be installing a tranny cooler soon. I had a couple questions before I placed the order. I live in Massachusetts, would you recommend the bypass? What exactly is the benifit of the bypass? Even if you live in a vey cold climate is there a downside not having the bypass?

I was looking into purchasing the Flex-a-lite 4120, how has this cooler been working out?

Re: Tranny cooler installation
 

I can't speak for the the Flex-a-lite 4120 as I purchased the Tru-Cool Max cooler. I live at 9000ft. elevation in the Colorado Rockies (yeah, it gets real cold here on occasion!), so I ordered my cooler with the bypass option. The bypass is supposed to work in the same way the coolant thermostat in your engine works, i.e. it wont open to allow free flow of tranny fluid until the tranny has reached operating temperature.

However... I had nothing but problems with the bypass on my cooler. Tranny usually ran way too hot, so much so I thought the bypass unit was defective so I ordered a replacement. The replacement bypass unit wasn't any different and the tranny temps were still way too high even in cold weather so I re-plumbed my cooler without the bypass and never looked back.

Yes on really cold days it takes much longer for the tranny to "warm up" but in my case I never take my H2 on short trips so it doesn't really matter to me. What does matter to me is I wheel my "Deuce" hard on trails in Moab often in hot weather conditions so I need maximum flow of tranny fluid through the cooler and that isn't going to happen with the restriction the bypass unit places in the circuit.

Just my $.02

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I pulled the car in the garage this weekend to have a look at the bypass procedure before I purchased everything. I have a 2005 H2 and noticed that I already have a stock external tranny cooler. Is there any reason not to just bypass the radiator and still use the stock tranny cooler?

Re: Tranny cooler installation
 

It's that thing in Step 1 above (post #2).

Re: Tranny cooler installation
 

Correct. What is the cooler in Step 1 above, which is attached to the two vertical brackets? I believe the power steering cooler is to the right of this cooler. Also behind this cooler is another cooler then the radiator. What are they all for?

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Re: Tranny cooler installation
 

Well done Egan, and I stand corrected, there definitely was/is an OEM external tranny cooler:

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It's a wonder any air gets to the radiator.

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so why has no one just bypassed the in radiator portion and just used the OEM tranny cooler? Is it not efficient enough on its own without the radiator portion??

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Thanks for all the help. I am at a standstill right now. I was thinking of the aftermarket transmission cooler. Now it looks like it may be possible to utilize the stock transmission cooler and just bypass the radiator all together. This seems like the simplest solution to fix any potential fluid mixing issue. Does the radiator add any additional cooling for the transmission fluid which would pose a problem if bypassing with the stock cooler? As Lojac mentioned is this less efficient which would require a larger aftermarker cooler?

On a side note I do not take my H2 off road and very rarely, if ever, tow anything significant for long periods of time. I really just want to fix a potential issue with fluid mixture so I know my transmission is safe in the long run.

Re: Tranny cooler installation
 

I've been on this and all the other Hummer forums for several years now and I've never read a post or a thread where anyone has bypassed the radiator portion of the tranny cooling circuit while keeping the stock cooler. I myself would not feel comfortable doing it, just looking at the stock cooler it looks pretty small.

You could always go ahead and do this and become the first "beta tester"! :D

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Normally I would jump at the shot to give this a try. However I was trying to get this all done before I head on a road trip. Don't really want to beta test anything being a thousand miles away from home.

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Off topic but...

To the guy whose H2 is in the picture a commong problem with early H2's was the hood straps rotting out because of the factory "sleeve" over the wire, which was corrected but cutting the sleeves off so that the metal cables could dry properly.



And I'm very intrigued on using the stock cooler, my 03 is still under warranty and I don't want a reason for them to deny fixes so I'm waiting til it is almost up, which it is now getting to the point that it is almost up...

Re: Tranny cooler installation
 

I spoke with a local transmission shop about the issue I am having utilizing the stock cooler and bypassing the radiator. For what it's worth he mentioned the radiator is typically used to regulate the coolant temperature before it returns to the transmission.

Re: Tranny cooler installation
 

That would tell me that the factory cooler is more than likely sufficient as is.

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I would imagine so especially if you rarely offroad or tow anything. I've been meaning to add an aftermarket cooler but I think I'll bypass the in radiator and see how the temps run.

The real test will be this summer here in AZ but again I don't forsee any issues using just the external.

I'll try and take pics when I start this project if no one beats me to it.

Re: Tranny cooler installation
 

so i am looking to add an external cooler to my 2003 H2.

here is a pic of my front end. it looks identical to the pic of the 2005 H2 with a external cooler ( OEM)

do we know for a fact this is an external Tranny cooler?

im not worried about bypassing the radiator and going to this cooler, as i am more concerned that if this is indeed for the tranny, i want to pull it out completely and install a bigger cooler right where it is located at and using the brackets in place to mount to.

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I am considering doing this also. Would I see any benefits by just replacing the stock cooler with a larger one and not bypass the transmission or do you get better cooling by bypassing the the radiator?

Re: Tranny cooler installation
 

The whole point of this is to bypass the radiator to eliminate the chance of coolant mixing with tranny fluid and destroying your transmission. The external cooler is an added benefit for better cooling.

Re: Tranny cooler installation
 

Thank you! Now I understand.

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so what level do you guys keep your tranny fluid at now with the cooler?

i had my cooler installed now for about 2 weeks, and this baby keeps the fluid cold.. well under 100 degrees.

so if the fluid is kept cold, it never expands.

right now, i have it just above the cold line.. like 1/4 a quart above.

im also chasing a leak somewhere in it, but can locate it due to the fluid slopping around for a little bit. so i power washed the whole area, and wiped down the lines in hopes i can track it. since i didnt cap off the internal rad lines, im guessing that excess leaked out, but i did have to add fluid.. so who knows.

but i am curious at what levels you guys run it at.

thanks

Re: Tranny cooler installation
 

I just keep mine at the "full when hot mark" when the truck is running at it's at it's hottest (about 140? - 150? for me).

Re: Tranny cooler installation
 

As I quickly approach the need I do this myself, I've been thinking; obviously what's there is flawed and must be fixed, however I looked into why it went the way it did, while in sure many have long since figured it out, I just felt reason to state what I found
The factory unit allows the teams to heat up faster when cold, it's just as important for the transmission to be heated to a level as it is to cool it.
The factory unit also cools by use of liquid which inheritaly (sp) cools better than air

So by using just the stock external you lose the heating properties and a certain amount of cooling

Regardless of this, the system must be altered

Re: Tranny cooler installation
 

im not sure that it is important for the tranny be heated to a certian level for operation. now if we are talking well below zero degrees, thats another issue.

i live in Minnesota, it is freezing or below freezing nearly half the year here. hell, we are expecting 8 inches of snow by tomorrow.. APRIL 11th !!!!
my tranny works and had always worked without issues when it is cold.

with my cooler installed.. i have seen the temp go up to about 120 degrees, but that is the max. 90% of the time though the needle doesnt move. it just sits right at the 100 degree mark.

by natural friction, the fluid/tranny will heat itself up to its rated viscosity. any additional heat besides that, that is the heat that needs to go.

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Anyone tried stock yet?

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120 just seems way too cold for the transmission