2013 Transmission cooling upgrade, thermostat, big rad, or fan?

I have a 2013 Tacoma with the factory external cooler.

As I understand it, there is a transmission thermostat on my year truck?
Does the ATF still flow through the engine radiator before going into the aux cooler in this year?

Recently I started off roading more in the mountains, and started doing very steep low speed climbs (probably a thousand feet a mile). After getting to the top of these climbs I noticed my transmission temps were hitting 205F !! Too high for my comfort levels, I would like maximum fluid life.
I have never seem it hit this high before, Highest I've ever seen is high 180s when going 70 up a couple mountain passes in 4th (locked). I guess the low speed (lack of airflow) really defeats the aux cooler.
I suppose the best thing would be to jump directly to installing a larger radiator with its own fan, but I want to explore some simpler options first.

If my year of truck does have a thermostat, does anyone make an aftermarket one that fully opens at a lower temperature than stock? I heard the stock one starts opening at 190, and fully above 200?

I also figure I could strap an electric fan to the existing aux cooler to give airflow while climbing steep grades at low speed. This is the easiest solution, but the aux cooler is such a small surface area I am unsure if this would be worth it.

For upgrading the whole cooler entirely, What do people recommend for fully replacing the aux cooler? Do people run electric fans on manual switches, or somehow hook it into a temperature sensor somewhere?

 

I do not believe the A750 trans has a cooler line thermostat, I'm pretty sure fluid flows through the cooler(s) at all times.

The engine thermostat opens at around 180-185 (at least my 14 does), I would leave that alone otherwise you may set DTC's.

If you need better cooling at lower speeds I'd go with an auxilary electric fan out front and possibly a larger trans cooler.

There's a writeup about trans coolers here and about the A750 in general here.

 

I added an aftermarket cooler in-line with the OEM aux cooler.

 

On the 2nd gen taco our 5 speed (which is also found on 1st gen tundras and others) def Does not have a thermostat. (1st gen tundras did)

Put a bigger auxiliary cooler on it and put an inline thermostat (derale makes one that opens at 160*f) keep it routed through the rad.

 

What do you think of bypassing the engine radiator loop, and relying on a ~130F thermostat to regular temperatures in the winter? This could give maximum cooling (without the problems of dumping engine heat into the atf) without overcooling the transmission. I'd imagine a transmission that has no external cooler (when thermostat is closed) would still heat up to decent operating temperatures in cold conditions. (My temp in the winter sits right at 134)

I think the existing aux cooler could also be more effective with this design?

 

Found this thermostat: https://www.improvedracing.com/compact-high-flow-engine-transmission-oil-cooler-thermostat.html

They have a 145F thermostat that would seem to work perfectly. I could disconnect the engine radiator lines, attach them to this thermostat as a first step. Then add a larger radiator with a fan later down the line.

 

Just make sure your thermostat is not blocking cooler line flow when it's closed.

 

Yep, the one I found above is just a U turn when cold and flow through the other side when hot. It says 5 GPM, can't find any numbers on the flow rate of the A750, but I assume thats enough.

 

I would not bypass the engine coolant heating up the trans fluid when cold. If you “wait” for the trans fluid to heat up on its own, you’re relying on fluid way below the range it was designed for.

I would put in a bigger trans cooler.

For your situation of 1000ft/mile, low speed, you’re likely better served by an electric fan and maybe an upgraded alternator.

Do you have the factory tow package? Those came with a bigger alternator and a trans cooler.

 

Yeah, I do have the tow package.

Isn't transmission fluid way below the range its designed for on a cold start anyways? Both the engine and transmission are close to ambient temperature, so the transmission fluid is going to be cold until the engines thermostat opens and begins heating up the transmission. Plus the transmission does its own heating with the torque converter. The difference being a few minutes maybe?

 

I'm running a

$52 Hayden 678 Universal Rapid-Cool 9.5” x 11” Add-On Transmission Cooler – Not for Direct Replacement of the OE Cooler

Hayden 678 in place of the factory trans cooler on my '13, been on there for almost 60K miles and no issues. Trans fluid stays nice & cool even when towing.

 

Honestly that does sound hot but was it that one hill, one time? How many times a year you doing that hike in the truck?

 

Sorry I should have clarified, this was just one example. I hit these hills at least once a week during the summer. Gotta climb to get the good views. This summer I am doing the climbs practically everyday. I try to take it slow, 1st or 2nd and keep it slow to keep minimum load on the torque converter. So far on a day below 80, I can keep the trans under 180 if I'm under 5mph.

My goal is to be able to push 20-30mph up a 20ish% grade for maybe an hour or two. Just a goal though.