DIY Trans Cooler for ~$300

I just installed a trans cooler on a customer's 2021 and wanted to share the process. I've seen kits recommended, but never the part numbers (granted I've never searched for that).

There's really only three parts you need:

1. OEM transmission thermostat (part #32970-34030)
2. A transmission cooler of your choice
3. Some rubber oil lines

I got my transmission thermostat off eBay for $140



For the transmission cooler I used a Tru-Cool 11x10x1.5 (per the customer's request) which was $94 from Kartek. There's some advantages to this cooler from a mounting perspective I'll get into later. But frankly, any old cooler will work and most coolers come with some zip tie mounting that lets you clamp it to the radiator if you want to do that. I've done that on my old trucks and they were fine.



And then I used some 3/8" hose and grabbed some 90deg brass fittings.


Onto the installation. The 2021 (and presumably earlier years) have a brick that takes the place of the thermostat from earlier trucks. There are three bolts you undo that sandwich both the coolant heating puck and the brick to the side of the transmission. Undoing these bolts does NOT spill coolant, but ATF will come out (not sure how much, I already had the transmission drained). The new transmission thermostat is a direct replacement and uses O-rings (as does the original puck) so no messing with gaskets and stuff. Very easy and seamless swap out.



Here's a picture of it installed and some hoses run to it, you can see the heating puck on the bottom. Anyone can swap this out in a couple minutes if you know how to use a ratchet.



Moving on to the cooler. Once the grille is removed (kind of a pain in the ass, you can figure out how to do that elsewhere) I pulled the passenger side air duct panel and that opens up a lot of mounting options. Purely out of coincidence, the passenger side mounting holes on the cooler perfectly line up with the holes on the body. I did have to cut a slot to clear one bolt midway up that you can see (I just cut two lines and then folded that piece forward).

On the driver's side, the bottom lines up pretty well with the bottom A/C condenser support bracket. I made a little bracket in a Z shape to tie into that, though there's a lot of ways you could go about that. Between the bottom mounts and a little support on the bottom driver's side, the whole cooler is sturdy enough I didn't bother mounting the top driver's side.



As I said earlier, there's lots of mounting options and it's dependent on the cooler. This way is very robust and easy and nearly free.


All in:

$240 + $94 + $30 = ~$365 for the whole setup, and you could run a lot cheaper or more expensive cooler if you wanted.

Trans temps after this were locked in at 190-200 while running a supercharger. I also left the thermostat pinned open, but that's a conversation for another thread.

 

Very interesting approach. Thanks for writing it up.

I am still on the fence about adding a cooler but th cost of this method makes it attractive.

 

Nice work, and good budget friendly option. Bought the Veepeak Bluetooth OBD2 thingy and use OBD Fusion app to monitor trans temp in my 2019 w/no cooler. Pan temps run 219-230 degrees depending on load. Put the 2019 up for sale and transferred the OBD2 thingy over to my 2000 w/factory cooler. Temps run 175-185 degrees. I've never even seen 200 degrees on it. If I were keeping the 2019, I would probably add a cooler this way to lower the temps some.

 

I installed a blower on another 2021 a few weeks ago, that thing would gladly run at 240deg which was insane. And that was tuning the transmission and adjusting torque converter lock up to try and keep it as cool as possible.

Something I hadn't realized was people said the transmission on 2019+ used engine coolant to cool it down. There is no coolant that flows into the transmission to cool it, the only heat exchange is the coolant puck that's bolted to the side of the transmission (and used to heat the fluid to operating temp on older trucks). Effectively the transmission has no cooling whatsoever in stock form, unless you count a little two inch span where the coolant buck is bolted to the side.

 

Thanks for posting this. Lots of options to get the transmission cooled. This is a money saver!

 

Pucks are proving to be very utilitarian around vehicles

 

@snivilous You only ran rubber lines? What’s up with the hard lines everyone runs then?

 

The hard lines makes it so you don't have to deal with rubbing and heat issues. Good routing and shielding will alleviate those concerns.

 

To add to what @Mdl said, the stock system uses rubber lines at the flex interfaces. In the stock configuration you have thermostat -> rubber -> hard line -> rubber -> cooler. This just replaces the hard line (and presumably an absolute pain to install) with rubber the whole way. Cheaper and easy to route.

 

I actually really like the rubber way vs the hard line. Was it pretty easy to run those in/out lines from the thermostat to the radiator?

I’m assuming it’s only 2 hose running from the thermostat to the radiator?

 

Correct, and very easy to run. I zip tied them in a couple places along the way. Mainly keep them away from the CVs, tie rod, and exhaust. On this truck there were even a couple brackets where the rubber/hardline would normally go through so I ran the rubber through those spots. It was really straight forward, and I used maybe 15ft of hose between the two sides altogether.

 

Now we’re talking… if it was on your truck, would you just run the 15ft of rubber hoses or run the hard lines?

 

Oh rubber hose hands down. I did on this truck the exact way I would do my own truck. On my personal truck I have the oil lines to the filter swapped out from hard lines to rubber lines since it was easier to do that when I installed the supercharger, and there's a LOT of stuff the rubber lines can get caught on over there. But some zip ties or P-clips go a long way to keeping everything where you want.

With that said, nothing wrong with hard lines, you can look up the part number and order them.

 

I may go your route with rubber lines. I have all the part numbers, just debating which one would be easier.

 

Do the rubber lines, and if you don't like it then order the hard lines and swap it out. If the rubber is really bad, then just put a small loop between the nipples on the thermostat until you get the hard lines. Best case you save money and effort from the hard lines, worst case you go another week without a trans cooler.

 

If you go the hose route you can get some shielding/wrap/braid or whatever to give piece of mind if any spots look like it may rub.

 

Nice job! I’m currently collecting parts to add a cooler to my sequoia, which is completely devoid of one like ‘19+ tundras. Looking at my transmission temps driving down the freeway last week without a trailer was appalling. My plan is virtually identical.

On a related note, what is your opinion (or maybe general consensus) on cooler placement for those who have the cooler integrated in to the AC condenser - add the cooler BEFORE or AFTER the AC condenser? I’m thinking before simply to relive give some relief to the AC system on hot days at low speeds and high loads. My AC will warm up a few degrees sitting in traffic on a hot hot day, especially after working the motor or transmission hard. But after the AC condenser would probably provide better cooling for the transmission?

 

Nice!

Man, that eBay thermostat is cheaper than I found mine for back in 2020 when I pieced my kit together.

I’m going to help my neighbor install a cooler on his ‘20 Limited. We’ll probably go this route.

 

I've mostly seen the addition of a trans cooler goes after the ac condenser. I thought I read that the outlet line from ac to trans cooler needs to be under 4 inches or it doesn't cool as well. Forgot which thread gen3 maybe?

 

Any suggestions on the 3/8 hoses? I actually have a

$58 Hayden 679 Universal 11” Rapid-Cool Add-On Transmission Cooler to Enhance Cooling (not for direct replacement of the factory unit)

Hayden 679 cooler that’s waiting for install.

Now I can get the Stillen CAI and also get a trans cooler going.

 

Just purchased this for $132 on eBay.

@snivilous If you don’t mind, could you shoot a few photos of how you ran the rubber lines on the bottom? Just want to get a visual. Or unless if it’s on your build page.

Thanks!

 

I do not sadly, and don't have access to the truck anymore since I was doing the install for someone else.

You'll get it figured out, there's lots of room and places to run the lines. I ran them down parallel to the power steering lines and then over and zip tied to the dip stick tube and then back to the thermostat. Everything is pretty easy to reach from the back, through the engine bay, and reaching up through the CV/Tie rod area.

 

@snivilous Are the Napa hoses sufficient? Or should I go with Gates?

 

I would use anything as long as it's not vacuum line. I don't think brand matters, just something rated for oil is the main thing. Mine came from napa just out of convenience.

 

I checked to see how long it’ll be from the radiator to the thermostat and we’re sitting about 5-6’ total in length. I know you mentioned using <15ft of line.

The Hayden cooler came with Gates hose, but unfortunately not long enough. I’ll probably just pick up 15ft from Napa this upcoming weekend.

Now what I’m wondering is if Napa is actually selling 3/8x25ft for $6.49… or if this is a description error…

 

Has to be per foot, hose is like gold.

 

Wild.

 

Right?! I was about to say I must have been played for the fool paying $3 or $4 a foot from Jegs online (had some other things to order so I tossed in some line).

 

Yea this reminds me to buy some hose off Amazon, I went into napa the other day to buy 10ft of a bunch of sizes so at least I'd have spare laying around and ended up with a $150 bill!