How to lower your trans temps

I decided that I would like to investigate ways that I can lower my trans temps to add more safety buffer region during hard use. So, I thought of some ideas and set up an experiment to compare their efficacies.

Test procedure: Drive a loop of road that consists of 4 miles at 45mph, 3.5 miles at 60mph, numbers recorded while passing by a land marker at the end of the combined 7.5 miles, then travel 5 more miles to return home. All attempts were made between midnight and one to avoid traffic and have more repeatability of the weather. Ambient temp was always between 70-75 F. No additional load other than just the vehicle.

The measurements taken at the land marker usually didn’t change more than 0.1 F for a mile before or a mile after, so its convincing that everything fully reached temp. Heat soak of the engine didn’t seem to be a factor for the transmission. The first three runs were not from a cold start, and this can be seen in the different intake temperatures. I had driven the same road on days prior and noticed the same temperatures. I used one of those Amazon obd2 scanner to make measurements.



*None of the numbers presented here are concerning temps, but the experiment is more controllable under low stress conditions. This is also cooler than what I see just driving around on the daily, so I’m not concerned about over-doing it.


ATF oil change:

I did a pan drain and fill of near 3 qts.


Ducting to A/T Cooler:

The factory cooler location is mostly obscured by the bumper. This is a 3d printed duct I made that connects the grille opening to the AT cooler.








A/T line insulation:

They’re right next to the catalytic converter. I believe this is the only section that would benefit from it. The remainder of the hard lines are pretty close to fresh air.



Product I used from amazon:

$10 Heat Shroud Aluminized Sleeving Heat Shield fuel line wire heat sleeve 3/4" I.D. x 3FT with 10 Pcs 7.8" Stainless Steel Cable Metal Zip Ties

https://www.amazon.com/gp/product/B093CXPCVH?ie=UTF8


Things I learned:

Once your transmission is fully heat soaked, it is much harder to cool down. The fastest way to get your trans temp down seems to be to drive above 45mph without stopping. Every time I pulled off to stop it went up 30 deg as I went through my residential area, and letting it sit takes hours to drop significantly in temp. I imagine that insulating the lines will help as I suspect that exhaust heating the trans is a large factor at low speeds. Switching to neutral builds more heat than just letting off the gas.

In order of importance:

1. Regular ATF maintenance

2. Insulate the lines

3. Ducting

 

Great first post and welcome to TW.

 

This is very cool and interesting take on aiding trans temps! Thanks for doing the work to get to the point to make this great thread post!

 

I've always been curious how much our ac and general cooling temps would be affected but some ducting. Found it weird 4runners come with it but tacomas don't have any real ducting.

This lends some credit to that thought

 

Great post.

Was each method done on its own, or were they combined? I'm especially interested in the heat shield. I think I need to upgrade my transmission cooler either way.

 

Impressive improvements, especially liked the testing.

 

@WormSquirts, The table rows show in chronological order what I did. So #6 is stock + duct on + trans service (grille back on), #7 is really all of the previous methods combined with heat shield in addition (with factory grill still on). I wonder if the trans lines were routed by the exhaust intentionally to get to operating temp faster because there's a heatshield on the passenger side catalytic converter but not the drivers side. I will probably remove it for the winter. I would really like to try a before and after comparison with the heat shield in hot weather for a longer harder drive but it hasn't been convenient for me to do currently. Maybe I'll post back in a month with that.

Another thing I have noticed is that it runs cooler at 60 mph than 80mph. I think there's a lot you can gain while retaining the OEM cooler, especially because many after market ones are tube and fin which are much lower in efficiency. If you have a lot of miles you may even find a lot of benefit in just removing the OEM one and shooting solvent through it to clean out any gunk blockages. I'm convinced switching to amsoil atf was by far the best first step.

 

For Tacoma ATF fluid, what temp is too high and for how long?

 

I would change what you're doing if you're pushing over 200. Generally oil turns acidic twice as fast for an 18F increase in temperature. There's plenty of opinions you can find about drain intervals on this site or in the manual.

 

I just push big 37s with a lot of extra weight and spend a lot of time in 4low, so I definitely hit the limit of the current cooling system

 

my 3rd Gen rests at 184-194, not sure what is accurate, but I’ve heard the ATF fluid can hit 240-250. I’ve hit 210-220 multiple times

 

@SpeySquatch, I've read the gen 3 trans are intended to run a bit hotter than gen 2. Gen 3 also has a thermostat as standard to avoid overcooling when not needed, so is likely part of why.

 

I pin my thermostat when I tow and it makes 184 when resting vs the norm 194. It has the tow package, but I’m starting to think it is somewhat worthless if 10 degrees is all the change it makes…just means sooner fluid changes. What you said makes sense

 

There are various temp/life charts for trans temps...
The main thing I learned by asking the tech dept at Mobil Oil... tran temp life expectancy are based on constantly running at the stated temp. They specifically emphasized that moderate spikes do not have a notable impact on the lifespan of the tranny fluid.

The above being said I noted my 2021 often had a pan temp, at highway speeds, of 195'ish. With a cooler at 190'ish. Either way I would estimate a shorter lifespan of approx 50k-60k.

 

this was going uphill after a day of fishing not towing anything with the TC at 214 (not in ECT) and the other on the freeway doing 80 for about 30 miles. When I pin my thermostat I see about 10 degrees cooler from the tow pkg cooler

 

If that

The TC temp will climb fairly quick when going uphill, even without towing. It will also go down fairly quick if the pan temp is not too elevated, which was a big reason I got a cooler... to help keep the pan temp down when going up long inclines.

Also, when 5th or 6th does the unlock (partial shift) like when up a very slight incline, the TC temp starts to climb very fast. If you drop to 4th it will go down fairly quick.

 

problem is. Can’t get down to 4th towing my trailer up the grades which is why a TC lock in 3rd would be a cool ECT option.

what do you mean by cooler? I have the little tow cooler that came with the TRD tow package. Is what you are mentioning bigger or something?

 

In my 2015 I, like many others, supplemented my factory ATF cooler with a larger cooler as the one provided stock was generally considered to be a bit too small if towing often. On my 2021, Toyota only uses the radiator to cool the ATF. I added an additional Tru-Flow cooler.

On some moderately steep hills, I find shifting into 3rd or 2nd (prior to when the auto function would do so) to be beneficial. The TC temp will still climb, but I find that it climbs to 215-220'ish and holds more steady there and I can run at a lower rpm (usually about 3k-4k) when climbing.

 

Welcome to TW, ive added 2 aftermarket coolers and currently in the process of adding a 10inch fan as well. I don't usually see temps above 200 with current setup even while in 4lo offroad but adding the fan will certainly help not even getting close. When its about *75-*80 outside my trans stays around *150-*180 depending on city or HWY. Make sure you have your system flowing upstream instead of down as it helps with cooling more.

 

Here's an old trick. Set up a set of misters to spray water onto the tranny cooler and radiator. It's fed from a used windshield washer bottle and pump. Knocks temps right down. They probably have kits these days.