Tranny Cooler Upgrade Planning (1 Viewer)

[TeCKis300]

Not sure I've seen this done and could use some help brainstorming for an upgraded candidate transmission cooler.

I'm towing outside of design parameters at 15,620 lbs total weight (GCWR rated 14,920 lbs). While the stock system is coping, tranny temps are getting elevated (266°F+) in extreme grades on the freeway that it's probably a good idea to upgrade the transmission cooler. See post #2 about tripping tranny temp protections. Engine radiator temps are reasonably steady going from low 190°F to 203°F when on grades and holding 4k+ RPM for 30 minutes at a time.

Our stock tranny cooler measures 7 1/16"W x 13"H x 1 1/4"D. Or 114.7 cu in of radiator volume.

A natural donor could be the Tundra 5.7L that shares similar architecture, and is rated higher at for 16,000 lbs GCWR. It's tranny cooler measures 6 9/16"W x 17 15/16"H x 1 1/4"D; 147.1 cu in. radiator volume. Or 22% larger than our tranny cooler.

Question - any recommendations as to how much larger I should aim for? Any particular coolers or recommended brands?

Thanks to measurements and pics from @MTKID

Tundra 5.7L tranny cooler measurements

The tranny cooler is on the passenger side and is shrouded to ensure airflow.

 

[TeCKis300]

Cross posting from another thread that has details of tranny lockup logic once the first high temp thresholds of 266°F torque converter temp and 203F engine coolant are exceeded. As hard as I've pushed the car, fortunately have never seen the 302°F warning threshold.

Got to see the torque converter handling of heavy loads in action on a recent tow trip. Laden with 6 people and a 27' Airstream for a long 10-day trip, CAT scaled at 15,620 lbs. Ambient was 90F+ in areas. Combined with some big grades in the west, I was curious how the torque converter manages heat. For context, I'm on 35s, re-geared with 4.3s, effectively factory gearing.

View attachment 3136778

From discussion in another thread, here's the factory logic. I crossed the 266F ATF and 203F coolant threshold. Note there's two ATF temps, one in pan and one at the torque converter.


Climbing a long 14-mile grade at ~6% and keeping 60-70MPH speeds. Meaning downshifts from 4 to 3, and even to 2. (5.7L is a beast holding fwy speeds on grades with almost +10k lbs load).
1) Transmission temp at both pan and torque converter when locked at cruise is typically ~195F. Coolant ~198F.
2) Once the torque converter unlocks hitting the grade to get a bit more gearing, the torque converter temp spikes to ~225F
3) On grade torque converter stays unlocked. Torque converter temp will continue a steep climb, to 240, 250, 260F+. While pan temp absorbs the heat climbing steadily. Coolant stays mostly steady and may climb very slowly a few degrees.
4) Trip threshold of 266F torque converter temp and 203F engine coolant
5) Trans ECU now aggressively will lockup torque converter. Locking 3rd, even 2nd. Torque converter temp drops aggressively tracking closer to pan temps. And both will very slowly climb in unison if grade continues. Or can steady up around 230-240F and is manageable if letting up a bit.

Highest temp snip on my OBD Fusion dashboard. Crossed threshold shortly after.
View attachment 3136773

Here's torque converter lockup in second gear at 60MPH (indicated by blue horseshoe around 2)
View attachment 3136771

 

[daneo]

Have you reached out to Wholesale Automatic in AU? Wholesale Automatic Transmissions - https://automatictransmission.com.au/
The owner, Rod, has a 79 and owns (owned?) a URJ Lexus LX570. They build transmission coolers for just about everything and could get you a kit for your LX.

LX570 5.7L V8 with 6 Speed Auto

Choose from a range of great products that suit this specific vehicle.

automatictransmission.com.au

 

[04UZJ100]

Isn’t the cooler on a 100 larger than the 200? May be an OEM option.

You can also bypass the actual radiator loop as that essentially limits cooling capability. You’re circulating 266F fluid across 190-200F coolant. Not much of a delta-T there.

I have never considered the coolant radiator supplemental cooling.

 

[bloc]

You can also bypass the actual radiator loop as that essentially limits cooling capability. You’re circulating 266F fluid across 190-200F coolant. Not much of a delta-T there.

I’m not totally sure but isn’t the bottom tank the cold one in our setup? Wouldn’t that make the temps there significantly less than the water temp within the block?

Even if it isn’t much of a delta this one being fluid to fluid there is tremendous capacity to remove BTUs, and it’s pretty constant, independent of vehicle ground speed for instance. Though teckis has said temps tend to go up at higher speeds on our rigs.

 

[Moby]

Have you reached out to Wholesale Automatic in AU? Wholesale Automatic Transmissions - https://automatictransmission.com.au/
The owner, Rod, has a 79 and owns (owned?) a URJ Lexus LX570. They build transmission coolers for just about everything and could get you a kit for your LX.

LX570 5.7L V8 with 6 Speed Auto

Choose from a range of great products that suit this specific vehicle.

automatictransmission.com.au

I wonder if upgrading the VB is worth considering as well. More holding power/less slippage/less heat. I loved the Wholesale VB that I put in my A440 (before the H55 swap). I'm really hoping they eventually do a VB for the 8 speed.

I ran an additional cooler in series with the OEM in radiator cooler in the A440 as well. It would bypass the cooler when the temp was cold and let it flow past the trigger point. I don't think I'd deal with that hassle though, I'd get one of those Wholesale coolers if they are factory fit.

 

[TeCKis300]

Looks like @Mago had installed one awhile ago for reference.

Transmission Cooler (Radiator) Upgrade

Been over a year now since I installed a larger transmission cooler with a thermostat and a cooling fan. Since I've had it running without trouble, thought I'd post it here.. could be useful for those towing or getting stuck in hot climates. Used to overheat transmission oil. Now, even with...

forum.ih8mud.com

Thinking out loud, random thoughts and trade space
- Keep the radiator loop in play. As I intend to visit cold weather destinations and maybe Alaska one day. So as factory as possible with some supplementation
- Still debating whether to replace or add to the factory tranny cooler
- KISS and cheap
- OEM radiator if possible as IMO, they are built to another standard than what's commonly found in the aftermarket. Though there's some good aftermarket brands out there too
- Minimize stacking/shrouding and impacting the engine radiator performance. Don't necessarily want to trade better tranny cooling for worse engine cooling as the engine is getting a workout too. There must be a strategy to Toyota mounting the tranny cooler on the far passenger side, with possibly hotter radiator fluid entering from that side.
- Thinking there may be an opportunity to locate a second tranny cooler plumbed sequentially after the stock cooler. Place it over the condenser fan so it can have partial active cooling.

Isn’t the cooler on a 100 larger than the 200? May be an OEM option.

You can also bypass the actual radiator loop as that essentially limits cooling capability. You’re circulating 266F fluid across 190-200F coolant. Not much of a delta-T there.

I have never considered the coolant radiator supplemental cooling.

It does appear to be rather large. Couldn't find any firm dimensions, but will continue to look.

 

[TeCKis300]

lol. That’s gotta be my least favorite photo. All my work junk spread out in front of it. But I’ve got nothing better currently

Haha, gotcha. Replaced the photo with one from my own stash. I still think your photo is awesome!

 

[Boston Mangler]

Not familiar with the routing of the trans lines in a 200, but if they'd fit, what about what of those finned, inline coolers like many race trucks/cars have

They come in 100s of different shapes and sizes and been used in the race world for decades.

In many cases they actually add a little fluid capacity also.

Also a lot more stout and less chance of damage from road/trail debris than the stock style.

I am talking about ADDING one, not replacing stock with one

Just an Example:

 

[mallspecLX]

Just more food for thought - I just installed this kit into a 2019 tundra. Toyota deleted the transmission cooler for the 19 through 20 model years. I tow an 8k lb travel trailer and have never seen temps go above 200 with this kit, the hear exchanger is big.

The other thing to consider is toyota has seemingly decided that 250 degree transmission temps are ok for the Asin 6 speed - and the tundra forums are mixed as to whether this is true. What i can tell you is i haven't seen evidence of increased transmission failures in these later model year tundras despite the cooler delete

 

[mallspecLX]

Sorry forgot link

Genuine Cooling Systems

Genuine Cooling Systems sells custom transmission cooler kits for the Toyota Tundra that bolt directly onto factory mounting points on your truck.

genuinecoolingsystems.com

 

[TeCKis300]

Not familiar with the routing of the trans lines in a 200, but if they'd fit, what about what of those finned, inline coolers like many race trucks/cars have

They come in 100s of different shapes and sizes and been used in the race world for decades.

In many cases they actually add a little fluid capacity also.

Also a lot more stout and less chance of damage from road/trail debris than the stock style.

I am talking about ADDING one, not replacing stock with one

Just an Example:

View attachment 3313479

We're on the same page and definitely have been looking at this unit for all the reasons you mentioned. The added fluid volume can help too as ultimately, it's about maintaining fluid life between change intervals.

Trying to wrap my head around packaging. not having taken apart things to measure where I'd locate it yet.

If I've studied this correctly, the flow is hot tranny fluid > bottom of engine radiator with a crossover pipe entering at the drivers side > exiting passenger and going to air-to-air tranny cooler > back to transmission.

Just more food for thought - I just installed this kit into a 2019 tundra. Toyota deleted the transmission cooler for the 19 through 20 model years. I tow an 8k lb travel trailer and have never seen temps go above 200 with this kit, the hear exchanger is big.

The other thing to consider is toyota has seemingly decided that 250 degree transmission temps are ok for the Asin 6 speed - and the tundra forums are mixed as to whether this is true. What i can tell you is i haven't seen evidence of increased transmission failures in these later model year tundras despite the cooler delete

Spot on. I do ask myself if there's a problem worth solving here. I could as easily increase fluid change intervals as another strategy for tranny life. Or back-off on power when climbing grades to mitigate continued increasing tranny temps.

That said, I do use my LX hard on both sand/silt baja style and towing. Blame it on the Raptors I hang out with. If I'm being truthful, I'm a speed junkie and backing off on throttle is not my style. I also tend to visit mountainous areas towing as that's reprieve from the heat in the southwest. I can readily get into tranny lockup logic on milder grades at 80*F. It's the 115*F towing extended 7-8 degree grades that make me think I should do something.

 

[bjowett]

I’ve been throwing this around….

Use an atf cooler from a Nissan Frontier/Xterra, it’s decently sized (13.5 x 8.5” x 1.25”) and has a built in thermostat/bypass. Run it in series as the last cooler in the loop. Given that the thermostat it uses is of appropriate temp(?), it will only come on line when needed. There are a couple of placement options, off to the side and dump the outlet into the wheel well, or in front of the radiator where the fan can cool it during slow speed maneuvers. Both have positives and negatives.

 

[Boston Mangler]

We're on the same page and definitely have been looking at this unit for all the reasons you mentioned. The added fluid volume can help too as ultimately, it's about maintaining fluid life between change intervals.

Trying to wrap my head around packaging. not having taken apart things to measure where I'd locate it yet.

The beauty of them is there’s literally 100s of different shapes and sizes

 

[linuxgod]

Unless you find a similar size radiator with similar mounting available which is deeper, I would look to add another radiator somewhere. My hunch says one of those finned coolers mounted to the frame just behind your winch might be nice. You could also buy a $50 Dorman cooler and try to mount it on the back side of the radiator in the engine bay (if there's space) so that the heat of the extra ATF cooler isn't then getting dumped onto the main radiator as I'm pretty sure the engine coolant temps are designed to be much lower.

Definitely subscribing to this thread as I've had similar thoughts with my truck. I've maxed mine out at 248-249F on a steep climb, but so I've not hit any of the limits officially, but it just feels wrong to run so hot. In fairness I think some of my heat is because with the metal bumper I don't have the same air scoop anymore that you have, so I think airflow is a bit reduced (which possibly explains why with the bumper but before re-gearing I seemed to run about 5F hotter than stock, though now after regearing when towing I handily run ~215F).

I am surprised the path is trans -> radiator -> ATF cooler and not trans -> ATF cooler -> radiator. I thought Toyota's idea was "cool as much as possible and then if the fluid is too cool we use the radiator to get it back to the preferred operating temp". I'm surprised it's the opposite.

 

[bloc]

I wouldn’t want a heat exchanger downstream of the radiator at all.. the surrounding temps will reduce any cooling ability.

Also the stock flow path makes sense to me, personally. We need to keep in mind it is still a cooler, even if it can’t cool the fluid to ambient air temps. We don’t want the fluid that cool. But the fluid:fluid format of the in-radiator cooler means a metric s***-ton of BTUs can be reliably moved from the ATF into a system with tremendous ability to transfer that heat to the surrounding air, facilitated by the large radiator core and cooling fan. The one problem I see here is ATF temp is most likely to be elevated when the engine cooling system is already being stressed and ability to remove heat is reduced. Another hypothetical problem is mixing of fluids with devastating consequences for the transmission if the core fails but Toyota did a good job designing this system.

IMO the air:fluid cooler is icing on the cake and a good target to further improve total system cooling.

 

[AnyMal]

Im not an expert by any stretch of the imagination but wouldn’t replacing for new put you back roughly where you want? I thought that these lose efficiency over time and use?

Also any options to fin the transmission pan itself underneath and route more airflow?

All that spitballing being said, subscribed for general curiosity, I neither tow nor leave pavement .

 

[linuxgod]

I think bjowett might've been looking at a larger pan at one point. the question is how low do you want your pan to sit?

I vaguely thought about putting a cooler under the vehicle somewhere if there's not enough space up front but I think the protection from impacts would be poor. right now the grill largely protects the cooler, but if it gets punctured by a stray rock and leaks your transmission won't last very long

I don't think our factory coolers really lose performance unless you never change your fluid. Even then I wouldn't expect much difference as your fluid gets filtered (unlike coolant) and is less corrosive or prone to causing rust (unlike coolant).

 

[bloc]

Correct, they don’t lose efficiency from normal use. Any routine reduction of the stock coolers would just be from buildup on the fins which can be addressed by careful cleaning.

 

[hdj105]

I think bjowett might've been looking at a larger pan at one point. the question is how low do you want your pan to sit?

Greetings from AU, there is a deeper pan available here, no experience with it or how much clearance is lost, but adds 3 litres:
Toyota LandCruiser 200, Lexus LX570 and Tundra 6 Speed AB60 Deep Cast Transmission Pan - https://automatictransmission.com.au/shop/toyota-landcruiser-200-lexus-lx570-and-tundra-6-speed-ab60-deep-cast-transmission-pan/