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Old 09-13-2020, 09:10 AM   #1
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Transmission Temperatures?


Anyone monitoring their auto transmission fluid (ATF) temperatures?

I have a 2019 Tundra that has no auxiliary ATF cooler which pretty much standard for HD use which I consider dragging a 7000 lb AS through the desert to be!

Hauling a 22 Sport with a Tacoma I was getting 180° max in desert conditions. Tundra driving on rolling hills, 75° ambient temps, NOT towing I'm getting 220° to 235°. As low as 200° on flats.....

I wasn't so concerned and have not monitored while towing but will be doing that later this week and find out.

Curious about what other makes and models may be running at. I'm confident most other makers have some sort of ATF cooler and Toyota did till 2019....

I'll be installing a kit assembled from genuine Toyota parts from pre-2019 models in the coming weeks....


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Old 09-13-2020, 09:22 AM   #2
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2014 Tacoma and BCX

My ultra gauge reports pan temps at 175-185 at highway speeds in fourth gear on the flats and rolling hills. Converter temps are temporarily higher when climbing hills. Temps are considerable higher when pulling thru hills at 25-45 miles hr, sometimes as high at 205. Ambient temps 80-95. Pan temp rises quickly when pulling in fifth gear unless the highway is absolutely flat or going downhill. My Taco has a tow pkg with a trans cooler. Engine temps 199-202.
Wow just read my post, sounds like I need a hobby!
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Old 09-13-2020, 10:07 AM   #3
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Typically integral transmission coolers that provide their cooling via being by the vehicles antifreeze/water radiator do a poor job in cooling due to the transmission being subjected to temperatures that are affected by the rise and fall of the water temperature. In addition the water/antifreeze temperatures are also negatively affected because the air conditioner radiator usually sits in front of the water/antifreeze radiator which means that heat from that front radiator preheats water/antifreeze mixture.

Some vehicles have their transmissions attached to a separate radiator that sits slightly below the water/antifreeze. My van's towing package came with an external cooler that sits in front of the air conditioner radiator thus getting the best air flow to cool the tramsmission fluid.

Prior to my current vehicle I always added auxiliary coolers on my tow vehicles. The current crop of external coolers have special valves that automatically shut off the fluid flow during initial engine run time cold weather.

I used Hayden coolers on all my vehicles. They make good stuff.

The optimal temperature range for transmission fluid is 175 to 220 degrees. Above that, for every 20 degrees bad things happen, starting with formation of varnish at 240 degrees, followed by seals hardening, plates slipping, seals and clutches burn out, carbon is formed, and, ultimately, failure. I just got back from a visit in the Branson area and ran into some heavy traffic on the highway leading to Branson. My radiator water temp was almost 240 on some of the long slow pulls as traffic was traveling at 20 mph or less. Was happy to have that external cooler rather than an integral one.

Towing in OD for some transmissions can generate additional heat The way towing in overdrive can cause damage is when the torque converter keeps locking and unlocking like when going up hills with a large load. Unlocked it starts generating excessive heat, which in turn can burn the transmission fluid and cook your transmission. My transmission is sized to allow towing in OD, but I in hilly terrains where there could be a lot of shifting or on long hills, will manually pull the transmission out of OD to minimize the shifting. Typically the manual that comes with your tow vehicle will provide information if towing in OD is advisable.

A sign if overheating is occurring is by the color change of your transmission fluid. Typically it is pink and will turn darker as the fluid gets overheated. If it brown in color, it's lost most of its lubricating capabilities.

In towing I have never fried a transmission even though early in my experience I was towing with passenger cars or vehicles that had internal radiator transmission coolers. I attribute that to the use of external cooler.

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Old 09-13-2020, 10:36 AM   #4
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Most often the trucks computer will take steps if the transmission, among other systems, is about to cause damage. No doubt there is an idiot light and most likely the system will throttle down if it senses damaging temperatures. I'd suggest two things: check the temperature manually with a infrared heat gun to make sure you are getting real readings. And I'd go on over to the Tundra group and read up on what they have posted about towing and transmission temperatures.
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Old 09-13-2020, 10:53 AM   #5
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^ That pretty much says it all. There are some transmissions designed to run at 200-220 and have fluid that does not experience issues til 250 or so but for most including the Tundra 240 is the magic number to stay below with 170-180 being ideal.

My Ram Diesel runs at 176 towing or not. Steep grades at speed it will clime to 180 or so. On winding, rolling roads at 35-45 mph while towing it will heat up to 200 max
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Old 09-13-2020, 12:08 PM   #6
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Toyota totally removed the cooler and left just the heat exchanger that cycles radiator fluid through a small "tuna fish can" sized unit. This was also part of the system that had some sort of ATF cooler. Tundras went through several designs before eliminating it altogether.

I have NO FINANCIAL STAKE in the following link but an enterprising young man has taken it upon himself to design an ATF cooler based on pre-2019 Tundras and had custom brackets made for a Hayden filter that mounts in front of the AC condenser. He's added detailed instructions and ships complete for maybe $100 more than you could possibly buy the parts yourself. No telling how long he will make theses BUT he also provides part numbers for all needed and you can take it upon yourself to fashion one as well. Here's a link to a thread and a LONG discussion about it:

I've gone ahead and bought one despite the expense and I ALWAYS upgraded ATF coolers even before I towed a 7000 lb AS!

I'm still baffled as to Toyota's removal of it! Even IF the transmission can do fine at 240° it WILL do better at 200° as it's still dependent upon the ATF fluid. I figure it would have cost Toyota very little in parts that they already have designed and most of us would not have noticed even a $1000 sticker price increase with a HD ATF cooler installed....

My delivery sticker as do ALL Tundra stickers clearly states "auxiliary ATF cooler". Numerous attempts to figure what is going on have been met with prolonged run arounds with uninformed CS managers of one level or another....

Still LOVE my Tundra and plan on keeping for the long haul which is why I have chosen to install the ATF cooler system.

I have one more tow sans cooler and will report before and after temps in a couple weeks.


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Old 09-13-2020, 12:57 PM   #7
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My Silverado 8 speed (maxtow) runs at 175 to 185* solo. Towing it runs at 185 to 198*. Twice, in the Rockies, during long steep pulls, I have seen 205*

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Old 09-13-2020, 01:26 PM   #8
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I'll just wish you well on your transmission temps.

Just got home from towing my 2007 Classic 30' Slide Out with my 2005 Dodge Ram 5.9L Cummins with a cast iron 6 speed manual trans and it just does it's job. 211K miles worth so far for trans only fluid changes.
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Old 09-13-2020, 06:22 PM   #9
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I run a 2002 Ford 7.3 Diesel W/80HP towing tune / 4r100 transmission with 297K original miles. I have a real tranny temp gauge as the instrument panel one is useless. The transmission runs 180-190 normally and I've seen 210 heading up over grades on hot days. If it hits 220 I find the nearest place to pull off and let it cool (I have a 1700 RPM tune that helps cool everything including the occupants of the vehicle when it's hot). It takes about 10-15 minutes at high idle to cool down to 200. I've never let it hit 230. - Brad
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Old 09-13-2020, 07:24 PM   #10
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Recent trip from Colorado Springs to Bozeman and back in a 2019 NV pulling a 27' GT - according to our Scangauge II, transmission temperature varied between 170 and 180. On long upgrades and downgrades, it would wander up to about 190.
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Old 09-14-2020, 09:21 AM   #11
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Thanks everyone!

I think it's crazy Toyota removed the ATF cooler.. Even IF it can tolerate 240° why design it to run up against max temp?! They actually program the idiot light for hot transmission at 302°! That's so far beyond red zone to be laughable!

A guy on a Tundra forum designed an auxiliary ATF cooler from existing Toyota parts and a Hayden cooler in a few hours. I'm baffled how Toyota would not just do this and charge us the premium! I paid $890 for the kit the guy made. He went the extra mile and had custom powder coated brackets fabricated and full instructions. I would not have blinked if my Tundra was $890 more and it could have been less.

Oddly this has ALWAYS been Toyota's Achilles Heel. They can NOT design nor adapt a design for a simple ATF cooler! They had issues with "pink milkshakes" where coolant would mix with ATF. They tried running it through the AC condenser.....It's a simple solution you could pay the intern to design.

Stunning how they can craft an otherwise bullet proof truck yet stumble in the darkness for literally decades about an ATF cooler!!!

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Old 09-14-2020, 10:21 AM   #12
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My 2019 Ford Expedition runs at 190-195 just tooling around town.

Towing, it is above 200.

Once, towing up a steep entrance to a mountain campground, it got up to 230.

I don't believe the Expedition has a transmission cooler, even though it came with a heavy-duty trailer package.

Seems designed to run "hot" and be OK.
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Old 09-14-2020, 10:38 AM   #13
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My Ford seems thermostat-regulated to 195dF. It does run hotter pulling my 25' AS in Summer heat, but I've not seem it go above 220dF.

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Old 09-14-2020, 11:42 AM   #14
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I had replaced the factory cooler with an aftermarket cooler. I shed about 15 degrees towing.

This is kind of a broad stroke, but it's a good *guide*.

A good oil to air cooler I would not be without. I would not rely on radiator to do much transmission cooling on it's own. If you drive in mountainous areas, you learn pretty quick that the trans can heat up fast and meet or exceed 200 degrees.

I also added a deep trans pan.

There are folks that would argue that running this setup in the northern climates will bring your tranny to a short life. I'm going on 15 years and 40-50k towing with my 3rd party cooler (without temp bypass), deep pan and fully synthetic trans fluid that has a low pour temp of -64F.

The goal is to keep the trans at or ideally below 200 degrees. Yes, the vehicles do have limp mode, but IMHO, by the time it gets there, you may have already shaved some life out of your tranny.

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Old 09-14-2020, 11:51 AM   #15
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Things change. Both the particular recommended fluid and the normal operating ranges are different for newer multi-speed automatic transmissions. They use lower-viscosity fluids than older designs and run them at higher temperatures so they offer even less friction, ostensibly for operational efficiency. They're also supposedly lifetime fluids, which seems counter-intuitive... run it hotter and never change it? Normal operating temperature on the GM+Ford 10-speed is over 200F.
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Old 09-14-2020, 12:04 PM   #16
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Here is a fluid you can believe you can use in the newer lower visc trannies (of course make sure it carries your specific manufac specs before using).

If I read it correctly, it has a low pour point of -85F?!

I also do not subscribe to the never changing the fluid out. 200F is not terrible, but I would have to look a the cooler GM is putting in. GM was putting in some really HD tranny coolers up till about 2000, then went to this little thing that prob saved them .45/vehicle. To me getting that 15 degrees back was well worth the price of admission, and it mostly bolted right into place. Only had to fabricate one cross mount (due to much bigger than stock).

I am a bit OC, but every spring, I pull out about 2 gallons and put 2 fresh gallons in, this way I always have relatively new fluid. I think waiting 75k to 100k to change fluid is not a great idea. I know too many people that realize after about 40-50k that the fluid starts to look bad, go and do a trans fluid change and more times than not, the trans fails (happened to me too way back in the day 100 or so years ago).
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Old 09-14-2020, 12:27 PM   #17
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We have a 2013 Ram 1500 with the 5.7 litre Hemi and tow package. The instrument cluster has a detailed display of vehicle parameters (tire pressure, coolant and oil temperature, oil pressure, etc.). After about 83,000 km. of towing, transmission temperature usually runs from about 83C (181F) to 87C (189F) when climbing long hills. I was once concerned when it climbed to 92C (198F) in stop and go traffic in rush hour on I-15 around San Bernardino. I remember reading here somewhere that constant shifting would increase the transmission temperature. As soon as the traffic lightened, climbing up to the El Cajon pass, the temperature dropped back to 87C.
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Old 09-20-2020, 08:47 PM   #18
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So I got an auxiliary ATF cooler installed today.

Driving in 100° Tucson desert 85mph up slight incline (not towing) I was getting 179° max.

Great improvement!

If any Tundra owners are concerned I HIGHLY recommend adding the cooler! A guy sells a kit on tundra forums which is mostly authentic Toyota parts and a HD Hayden cooler. Expensive but complete and takes a couple hours to install.

Attached is my ATF at ~15,000 miles. I topped it off before I took a trip with AS back around May and it was clear pink, not quite like the new on the left but way closer to that! So this cloudy stinking mess of ATF is from towing some long grades in SW summer....

Some indication this may be normal but I'm sending in to Blackstone Labs for analysis so will have a better idea of ATF health in a few weeks.

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Old 09-20-2020, 08:57 PM   #19
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Does your wife know you have her good pitcher and measuring cup?��
My Ford 10 speed gets so-so mileage until it warms up to 190 F. It seldom gets above 205 F even when towing on grades.
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Old 09-20-2020, 10:08 PM   #20
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Interesting thread. I checked my trany temps on a trip to Colorado from Kansas last week. I averaged close to 212 on the way out to Colorado in a headwind in tow mode and downhill averaged 206 degress. Never saw much different, even downhill in tow mode which downshifted as low as third gear (10 speed trany/ecoboost V6). Outbound ambient temps were in the 80's, return were in the high 60's.
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