DIY Aux Transmission Cooler

[TeCKis300]

As the stock 200-series already has an aux tranny cooler, perhaps this is better described as installing an aux aux cooler. The stock cooler is solid. I imagine this is niche for the heaviest of rigs or those that do more aggressive off-road running that really loads up the torque converter. From my monitoring, continuous high engine outputs is what largely drives heat into the tranny.

This is a follow-on to this planning thread:

Tranny Cooler Upgrade Planning

Also PWR make a twin cooler kit, it’s pricey and I’m searching for pics, but the details are here: https://shop.pwr.com.au/extreme-transmission-oil-cooler-kit-toyota-landcru Of course if the transmission was designed properly the torque converter would be locked much earlier, eliminating the...

forum.ih8mud.com

I've gone the path of adding an additional tranny cooler inline and sequential to the stock tranny cooler. To better support cooling when motivating 15,620lbs combined weight when towing an 8k Airstream. Instead of replacing the engineered stock aux cooler, I felt it better to retain the stock cooler as a known performance quantity. As not all coolers are created equal, it was hard to know if replacing it would result in x% cooling relative to stock, or possibly worse. By adding another cooler, I was guaranteed some percentage improvement over stock, and that's what I got. It was also important that I don't add so much cooling that cold weather performance could suffer causing the thermostat to over-cycle.

An important consideration was not impacting engine radiator performance, by over shrouding frontal area. Keeping the install simple and robust. Also to leverage active airflow for things like low speed crawling in sand, where the stock tranny aux cooler is outside of the radiator fan airflow.

The cooler circuit is now setup as

transmission > radiator > OE aux cooler > aftermarket aux cooler > back to tranny

 

[TeCKis300]

Parts List​

Hayden 4.5"x15"x1.5" cooler (2-row, picture is not accurate) Amazon product ASIN B000HE6ULMAmazon product ASIN B0BGCGBM78https://www.amazon.com/dp/B075VGSFMX
https://www.amazon.com/Beduan-Stainless-Splicer-Coupler-Fitting/dp/B07P2DLBPC

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amazon.com

https://www.amazon.com/STEELSOFT-Adjustable-Stainless-Sprinkler-Irrigation/dp/B0C4V66ZPL
https://www.amazon.com/gp/product/B007WMF0Q8

Optional larger Hayden 6"x15"x1.5" cooler (3-row)
https://www.amazon.com/Hayden-Automotive-1234-Heavy-Cooler/dp/B000HE8VPU

Prep​

1. Remove engine covers
2. Remove grill, by taking off single screw, plastic clips at side, releasing tabs all around, possibly a wire harness, and take off grill
3. Remove shroud off factory tranny cooler (this may be touch with the bumper in place on LX. Possibly impossible on LC?

Cooler mounting​

The 15" tall cooler fits just about within the upper and lower radiator bracket. Using the provided brackets, locate the upper to the bolt that use to hold the horn. Only need a small 2" section to support the support the upper. For the lower, drill a small hole and mount with an extra bolt and nut. This allows the new cooler to be easily floated and positioned with it's provided rubber mounts

For mine as I have an HWM, had to locate everything up by 1" so had to grind a bit of the upper factory bracket for clearance. But you get the idea.

​

Plumbing​

• Add NPT barbs fittings to Hayden cooler with sealant. Make sure to use another wrench to counter when tightening fittings
• Optionally spray paint cooler black (the fins are raw aluminum finish)

Taking the line off factory cooler nipple. You want the return line which is the lower one.

• Add a section of new transmission line off the factory cooler to go to the top of the aftermarket cooler.
• Add a section of new transmission line from lower exit of new aftermarket cooler, returning to a barb union coupler tied back to the factory return line

 

[TeCKis300]

Results​

On average, I'm seeing 5-20°F degree temp drops compared to previous towing temps.

It's hard to nail down exactly as there's so many variables like weather, route, and grade. I don't have a good sense of non-laden temps as I'm only usually monitoring when towing. This particular trip was in early summer with temps in the 90s.

Towing on the level, pan and torque converter temps hover in the 190s. Not that much lower and maybe about 5 degrees lower at cruise versus prior.

Torque converter temps are pretty dynamic, but there is definitely a bigger difference in pan temps staying lower and be able to sink heat in passing and grades with less or slower rise. Faster fall. Previously, when downshifting to 2nd in steep grades for engine braking, I could reliably see torque converter temps spike right to 230°F. Now I'm seeing that in the 210°F.

One of the main reasons for more trans cooling was for brutal long grades where I could reliability trip the torque converter lockup logic at 266°F torque converter temp and 203°F engine coolant. Once tripped, the transmission will aggressively lockup 4th, 3rd, and even 2nd gear. This greatly reduces heat produced in the torque converter at which point it tracks close to pan temps. Problem is the pan temps will continue to climb and I can get it over 250°F at which point I let up hovering around 4k engine RPM, giving into some mechanical sympathy. I've never tripped the 302°F threshold and credit to the robust OEM cooling as moving 15k+ lbs on 35s is some work.

With the additional cooler, I can still trip the lockup logic if I'm super aggressive with basically the gas to the floor and engine screaming near redline for 5-10 minutes at a time. Notice the computed HP and TQ at 413hp and 390 lb-ft (OBD a bit optimistic)...it's basically engine output that drives heat in the transmission and I'm flogging it at max output. I was sure I could trip the lockup logic as I've been able to do that even when it's 40°F in winter. So I was pretty sure no amount of extra aux tranny cooling can prevent that.

Where it earns its keep is that pan temps do seem moderated staying pulled down more. It doesn't feel like it will continue to march into higher temps even when caning it for extended periods. I did just touch 240°F and ran out of hill (Grapevine CA). Still would like to test it in the Sierra's in later summer, but it already feels more resilient.

 

[bloc]

And here I was thinking the stock aux cooler shrouding extended all the way to the condensor/radiator to ensure cooling fan airflow even at low speeds.. which is clearly not the case.

Good stuff. I'm interested in seeing the before/after numbers.

 

[doru]

Painting the cooler... Best is to use specially designed paint for heat exchangers. Ceraqote is one of the brands.

Looking to see the numbers.

Interesting Toyota designed the ATF cooling as both fluid to air and fluid to fluid. The first is efective for driving at speed the second for crawl.

Unlike other Toyota vehicles the ATF cooler in the radiator is cooled by the engine coolant not by air.

I'll post some radiator dissection pictures.

 

[TeCKis300]

Write-up done.

I imagine this is a niche application as the factory cooling seems robust. Perhaps only the heaviest of rigs or those that run aggressively off-road in sand or loose surfaces that loads up the torque converter and tranny.

Painting the cooler... Best is to use specially designed paint for heat exchangers. Ceraqote is one of the brands.

Looking to see the numbers.

Interesting Toyota designed the ATF cooling as both fluid to air and fluid to fluid. The first is efective for driving at speed the second for crawl.

Unlike other Toyota vehicles the ATF cooler in the radiator is cooled by the engine coolant not by air.

I'll post some radiator dissection pictures.

Good point on the paint. I gave mine a super light coat on the front side just to take the shininess away

I hadn't known there were diff types of ATF radiator setups. Looking forward to pics.

 

[linuxgod]

Why wouldn’t we put the new aux cooler before the radiator cooler? Seems like that would still pull temps down, and it would ensure the radiator still warms the fluid when it’s really cold out.

Note I’ve never seen my coolant temp exceed 203F. No matter how hot my a/t temps or engine oil temp get or the ambient intake temp, it’s always in the 196F-203F range.

 

[sleepycruiser]

Thanks for the write up. Seems pretty simple. I did something similar on my GX470 when I had it and the temp drops while towing were noticeable. I’ll likely do this as well and post up my thoughts afterwards…although I don’t have anything to test the trans temps…unless a BlueDriver will do it?

 

[Fisher23]

Nice !

I did that same kind of mod on my Dodge Ram diesel. Ran 2 OEM in series.

As for the comments on why put in in series .. in cold weather the rad just uses the thermostat to control the cooling. Makes no diff.

 

[TeCKis300]

Why wouldn’t we put the new aux cooler before the radiator cooler? Seems like that would still pull temps down, and it would ensure the radiator still warms the fluid when it’s really cold out.

Note I’ve never seen my coolant temp exceed 203F. No matter how hot my a/t temps or engine oil temp get or the ambient intake temp, it’s always in the 196F-203F range.

I did look into the ordering quite a bit. The consensus seems that by locating a cooler before the radiator, wouldn't see much added cooling for the tranny. It would be helping the engine/radiator which as you point out is pretty stable.

 

[daneo]

Is there a noticeable driving feeling difference when the trans is running in the “tripped” mode with lockup in lower gears?

 

[TeCKis300]

Is there a noticeable driving feeling difference when the trans is running in the “tripped” mode with lockup in lower gears?

Not really. I think I can hear the shifts being a bit more crisp, but no real feel difference. My other car is a manual so I'm reasonably attuned, but at high RPM, it feels pretty direct either way.

 

[doru]

Here are the pics...

The ATF cooler inside the radiator is completely contained in the bottom plastic tank of the radiator. That means it is only cooled by the engine coolant. So this is a liquid-to-liquid heat exchanger. Not necessarily a cooler as it can be a warmer when the engine is at temperature higher than the transmission, very likely in the winter and when transmission is not doing much work/speed. Here is a picture of the bottom tank after cutting the radiator in half (red color is from the cutting blade coating, not much coolant was left).

It's size is much smaller than the auxiliary factory cooler placed RH in front of the radiator. That is fine because a fluid-to-fluid heat exchanger is much more efficient than an air-to-fluid cooler.

The 2023 LX FSM is offering two maintenance procedures for engine cooling depending on whether the truck is equipped with the aux cooler or not. So it looks like there are 200 trucks out there that do not have the aux cooler, using only the cooler inside the radiator. It would be interesting to see which 200 are those.

 

[TeCKis300]

Here are the pics...

The ATF cooler inside the radiator is completely contained in the bottom plastic tank of the radiator. That means it is only cooled by the engine coolant. So this is a liquid-to-liquid heat exchanger. Not necessarily a cooler as it can be a warmer when the engine is at temperature higher than the transmission, very likely in the winter and when transmission is not doing much work/speed. Here is a picture of the bottom tank after cutting the radiator in half (red color is from the cutting blade coating, not much coolant was left).
View attachment 3382626
It's size is much smaller than the auxiliary factory cooler placed RH in front of the radiator. That is fine because a fluid-to-fluid heat exchanger is much more efficient than an air-to-fluid cooler.
View attachment 3382629
View attachment 3382631


The 2023 LX FSM is offering two maintenance procedures for engine cooling depending on whether the truck is equipped with the aux cooler or not. So it looks like there are 200 trucks out there that do not have the aux cooler, using only the cooler inside the radiator. It would be interesting to see which 200 are those.

Very very cool pics.

That's a crap ton of surface area. In a liquid-to-liquid exchanger, would practically guarantee that transmission fluid would be warmed or cooled to that of the engine coolant when passing through. The coolant temp is super stable and almost always at 196F-203F range as @linuxgod points out. So even way overheated trans fluid should be coming out at close to 203F in the worst situations.

So the only way to cool the tranny peak temps is to lower its pan temps. Cooling the tranny fluid coming out of the radiator to a lower value will do that which is why it's recommended the put the aux coolers after that radiator.

 

[Fisher23]

Where is the OEM aux cooler located? and anyone have the part # for it?

 

[TeCKis300]

Where is the OEM aux cooler located? and anyone have the part # for it?

 

[linuxgod]

Very very cool pics.

That's a crap ton of surface area. In a liquid-to-liquid exchanger, would practically guarantee that transmission fluid would be warmed or cooled to that of the engine coolant when passing through. The coolant temp is super stable and almost always at 196F-203F range as @linuxgod points out. So even way overheated trans fluid should be coming out at close to 203F in the worst situations.

So the only way to cool the tranny peak temps is to lower its pan temps. Cooling the tranny fluid coming out of the radiator to a lower value will do that which is why it's recommended the put the aux coolers after that radiator.

Well the trans fluid would get cooled down to 200F potentially but it might be hotter if it can’t exchange enough heat in the time it passes through the radiator. Consider if the radiator is 200F but the atf fluid passes through at 50,000 feet per second, there’s no way it would cool much. Obviously that’s a ridiculous extreme but the point is still that your atf fluid won’t necessarily get down to coolant temps

 

[TeCKis300]

Well the trans fluid would get cooled down to 200F potentially but it might be hotter if it can’t exchange enough heat in the time it passes through the radiator. Consider if the radiator is 200F but the atf fluid passes through at 50,000 feet per second, there’s no way it would cool much. Obviously that’s a ridiculous extreme but the point is still that your atf fluid won’t necessarily get down to coolant temps

1000%. Just saying with the size of that liquid-liquid cooler, it has a high likelihood to be pretty close to engine temp.

 

[bloc]

Also, the lower tank of the transmission isn’t necessarily at 200 even if the engine/cooling system is very good at keeping the block temp there. The upper tank will trend hotter, the lower tank cooler, as coolant flows through it and the fan and/or ambient airflow do the job of removing BTUs.

How much lower will depend heavily on conditions. But my point is the lower tank will generally be under 200f, helping the ability to remove heat from the ATF. Even if this isn’t fully adequate for some use cases.

It seems to me part of the issue may be that even with the ability to transfer a huge amount of heat, nothing is actually forcing the water through the fins of the cooler within the tank. Fluid dynamics would have it mostly flow around the cooler.. with some incidental flow through.. not the bulk of it though.

 

[MUDZLLA]

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