How to lower your trans temps

I see this has some interest so I'll try to improve some of the info on the original post to make it easier to use as a reference. I didn't test every possible combo, but each combo can be isolated from the original table, so here's one that displays that more clearly. I included the removal of the factory cooler for two reasons, some people may not have it to begin with, and so you can compare its size to some aftermarket ones that you may be looking at installing. Keep in mind that the factory location doesn't get a lot of air, so if you buy an aftermarket one and give it direct airflow that's more like comparing to my factory one with a duct.

They make heat shield that doesn't Velcro together, but you'd have to disconnect the lines to slide it over. It holds up great as far as I've used it and I think there are a lot of situations where you guys might find it to be good value. For example being on a trail at low speed where there's not much airflow, or if you just want a bit extra without much effort. Where I live it gets from -15 to 115, so I took it off for the winter. The left side catalytic converter has a heat shield over it and the right side doesn't from the factory, so I think Toyota intended that to help warmup similar to the water radiator pass through. You could leave it on year round if you're from AZ or something and don't mind.

I've tweaked a bit more since the original post, particularly for cold weather use but also some other cooling details, maybe if people are curious I could post more and do some comparisons when it gets hot.

 

Yup, its those slow days on the trail under heavy load when I imagine this would really shine. Definitely added to my summer list!

Also interesting that several others have noted pan temps about 100*F above ambient. I've noticed that on longer interstate drives ever since I programmed my SGII to read the ATF temps. Pretty handy metric to keep an eye on things.

 

Hey I know it’s been awhile since you made this post but hopefully you still get notifications. What size heat shield did you use on the lines? Did you just use the metal zip ties they provided? If so, how is it all holding up?

 

Hi xLOGREx, I used 3/4" for the lines where they pass by the catalytic converter and the size fits nicely. The metal zip ties they provide are nice and seem really durable. I have since changed the whole configuration as most of the original post was to investigate what's what before deciding on what I want to do long term that satisfies as many goals as I can. I've removed the heat shield on the trans lines by the catalytic converter because that spot actually helps the transmission initially get up to temp.

Maybe I can post photos of what I've done later but here's the summary

• Replaced the trans cooler with a larger one and no fancy ducting
• Added an external thermostat inline with the cooler in the front bumper area (this one: https://www.improvedracing.com/high-flow-engine-transmission-oil-cooler-thermostat.html)
• No heat shielding next to the catalytic converter to aid warm up
• Heat shielding on the rubber lines of the non hot side of the thermostat track to aid warm up

I like the setup I have now quite a bit, I've lived with it over a winter and summer now and the tranny gets to 100F over ambient in a few minutes in the winter and even towing hills in the summer it almost never gets over 175F. Funny thing is that the only time I've gotten it seriously hot since doing this was going up a pretty steep crawl/climb where I was struggling for grip and picking up wheels at times and this would have been the situation where heat shielding next to the catalytic converter would have really helped.

 

Thanks for the detailed reply! That would be great to see pictures.

I can’t believe you don’t get over 175F while towing. My truck didn’t come with a tow package and I used to tow a tiny 5x8 enclosed trailer and had seen my temps get up to 260F! Ever since then I’ve been crazy about getting those temps down, starting with a heavy duty mishimoto trans cooler with a fan.

I recently started towing a 19’ 3300# dry travel trailer and my temps weren’t too bad at 200-210F average and ~230F on steep climbs. I’ve been trying to look into ways to improve that and one thing I was going to try was pinning the thermostat when towing.

Every bit helps, I’m still thinking about insulating the lines by the cats like you originally did. The cooling lines still go through the radiator so that helps get the trans temp up right? Just a little slower I’d imagine.

 

From what I've read 3rd gen trannies are designed to run hotter than 2nd gen anyway and I believe they come from the factory with a thermostat with a temp range of higher than 175. Part of why I think mine stays pretty well at that temp is that I tried to look carefully for a nice and powerful cooler and ended up choosing this one in the long and skinny size (link) and mounted it down by the long and skinny grill section down by the license plate.

$315 Setrab 53-10744-01 ProLine SLM Range Oil Cooler 250mm HDR-to-HDR, 10 Row, M22 Ports

https://www.amazon.com/Setrab-53-10748-01-ProLine-SLM-Range-Cooler/dp/B07C62X855?keywords=ProLine+SLM&sr=8-1&ufe=app_do%3Aamzn1.fos.c3015c4a-46bb-44b9-81a4-dc28e6d374b3&th=1

Mishimoto makes some nice stuff but generally I think many of their generic products aren't very well designed but that's just me. One thing to remember is what type of climate you live in too and how much of your driving is short trips. If you never get cold weather then that side of it might just not matter to you

 

Oh yeah that makes a ton of sense, I didn’t even realize this was a 2nd gen thread lol! I’ll have to see if the trans lines run next to the cats on the 3rd gen and if they do I’ll wrap them up.

I’ve been pretty happy with my cooler, after a hard climb, when I level back out, I can drop 20 degrees in less than a minute it seems!

 

What is measuring your temps? Is this a scan tool, or...? I like the ducting idea, and it does improve airflow. I ducted the intercooler on the supercharger of my Miata and it helped the IAT's substantially.
How about just installing a larger trans cooler? Slightly more fluid volume to circulate; that in itself probably wouldn't affect operating temps much, but a larger cooling area certainly would, and temp increases from heavy pulling load would rise more slowly and drop more quickly as the load is relaxed.

I pull several different trailers, a 5x8 enclosed trailer, a 18' flatbed with a tractor and other equipment, and a 6x10 dump trailer. The dump trailer puts the greatest towing load on my truck. It's rated for 5200 pounds of load and weighs 1820 lbs empty, so fully loaded weighs 7200 pounds. That is more than my truck is rated to tow (I do have the factory tow package), and most times I keep the gross trailer weight to no more than 6500, the listed limit of my truck (2011 SR5 DCSB 4x4 automatic). Occasionally, when I haul mulch, the loading guy gets a bit "enthusiastic" and I get more than asked for. The trailer's volume equates to just over 5 cubic yards when loaded level with the top, mulch weighs in the neighborhood of 900 lb per cubic yard. However, piled up I can haul 6 cubic yards, putting the gross weight at around 7220, and much of the time, that's what I get. I haul locally, and usually stay at 45-50 mph. My trans temps in this summer heat stay around 175-185 F, measured by a Scangauge II, which shows me both the trans and torque converter temps.If I get on a long, or steep hill, my temps have gone as high as 220 on the torque converter and about 215 on the trans. TC temps rise and fall depending on the transmission shifting and how hard I accelerate with a load (which I don't do) and how long the load lasts. Mainly, it's not as stable a temp as the trans. When I drive the trans temps over 200-210, I drive around a little and allow it to drop before I stop and shut down, so the hot fluid has a chance to cool a little and doesn't 'cook' in the trans. I'm using Toyota fluid, did a full exchange about 15K ago, and my truck has about 126K miles. Engine temps haven't been an issue at all, it has never made it to 200 in any situation.

Towing at my truck's limit has been a bit of a concern, I want this truck to last and I try not to abuse it. It's my DD as well as my work truck. The heavy loads haven't been a huge issue for braking, as the flatbed and dump trailer both have brakes on both axles, and I watch ahead and brake soon and gradually. I'm considering exchanging the stock trans cooler for one about 20% larger, I feel that would work for me to keep my unloaded trans temps a bit lower, and the loaded ones would stabilize even more quickly and not rise quite so high.