ATF Cooler and Towing Questions

Last weekend I towed our new pop-up tent trailer which has a max weight of just under 4k lbs (picture attached) - well enough below the max towing capacity of the truck. It was a short trip, only about 30 miles with a difference in elevation of about 200ft. On the way to the campground (descending), the transmission temp got to about 185degF, with an ambient temp of about 85degF. On the return trip (ascending) the transmission temp reached 195degF, with an ambient temp of about 80degF. It looks like I have an ATF cooler on the truck. If I'm not mistaken it sits next to the horn and is about the size of an envelope. I'm relatively new to towing, and I haven't been able to find much online as far as the "nominal" temp range for the transmission while towing. I would assume that, as it's an OEM cooler, Toyota would have installed a unit rated to handle anything within the load capabilities of the vehicle - am I mistaken or just overly cautious? I'm having the transmission flushed this Friday, as it's been about 70k mi since I had it done. Just wondering if I need to consider "upgrading" the ATF cooler at the same time and, if so, what to upgrade it to. Any help/advice is appreciated.

Thanks!

 

the transmission cooler in this truck is controlled by a thermostat that is set to 180 degrees. You can pin the thermostat open and possibly see some lower temps.

 

195 isn't terrible but you don't really wana push it past that, transmission fluid deteriorates rapidly at temps much over 200 degrees.
Towing that much it would be a good idea to tow in 4th instead of overdrive to reduce stress on the torque converter clutch.
Alot of info about towing, coolers, and the A750 transmission in general in the threads below.

https://www.tacomaworld.com/threads...th-pics-for-second-gen-4-liter-trucks.289913/
https://www.tacomaworld.com/threads...l-toyotas-write-up-with-many-pictures.526283/
https://www.tacomaworld.com/threads/the-tacoma-towing-bible.4031/

 

Transmission temps vary by manufacturer. Tacoma keeps things pretty cool and based on what I've read under 200 degrees is pretty normal. My F150 stays at 200-205 even when not towing and 230 isn't considered too hot.

In the real world 4000 lbs is a sensible amount for a Tacoma to be towing. When you see the 6500 max tow rating listed that is under ideal conditions. At sea level, on level ground, and with only a skinny driver in the truck. Start adding passengers and cargo to the truck. Pull it at altitude or on inclines and the amount you can reasonably tow is reduced. Pull it up to Northern AZ around Flagstaff at 7000' and you'll be glad you don't have anything heavier.

 

That’s where my concern is. We’ll likely pull it up to Munds Park in a couple months and I just want to make sure I’m not going to burn up the trans trying to pull it up I-17.

 

https://www.tacomaworld.com/threads...l-toyotas-write-up-with-many-pictures.526283/

 

Accurate for the 2nd gen Tundra, not for the Tacoma

 

You'll be fine. I have put 7 cross-country trips on this guy in 5 years, it has set up camp in 22 states so far. So it's been pulled over a few hills. Granted its only a couple hundred pounds lighter than it's high wall cousin, but I have never had an issue with it.

 

This image is pulled from the Tundra forum but the same ATF is used on the Tacoma so it's a fairly safe assumption that the fluid safe operating range is the same with the upper limit of 221. Reaching 195 isn't anything to be concerned about.

https://www.tundras.com/threads/5-7l-transmission-cooler-kits.60550/page-40#post-2506785

 

@nd4spdbh thank you for calling out my mistake, I forgot where I was. My apologies and good looking out.

Edit: PLEASE NOTE I am driving a 3rd Gen so your experience may differ as the 3rd gens have a thermostat whereas the 2nd Gens do not. Apologies for the misinformation and any resulting confusion.

I tow 3500 lbs of overland trailer with a stock '21 TRD Sport AT and 185-195 is where the truck likes to sit (TP1 and TP2) on long hauls at freeway speeds. Even in the Rockies at 10 degrees F it hovered around 190-195 due to the thermostat as others have mentioned. 260 is the number you need to watch out for as the fluid will break down at that point and anything above will cause immediate catastrophic damage.

Check out this post in my build thread for some useful links at the bottom. I'm documenting a few of the common questions that come up on the towing forum and my experience towing with my Taco. You'll find useful links to the towing bible and a few other posts (not mine) at the bottom. I'm going with a Setrab 9 Series Cooler with dual fans under the bed when I move to Texas in the summer. I'll have pics and an install thread.

Edit: @EatSleepTacos 's post above mentions normal operating range of a Tundra. The key word there is "operating". It is normal to see temperatures up to 221F during normal operation. That does not mean the fluid goes bad at 221, it means the truck operates at those temperatures.

 

I flushed the trans and installed a larger cooler in series with the factory cooler. I tow and drive on beaches frequently so it’s just nice to know the trans can cool itself in those conditions

 

Thats what I've seen when towing with a factory tow package as well. I think my trans was slightly cooler at the same ambient temp. But I also have the csf 4runner radiator so that might contribute.

 

Both statements INCORRECT FOR THE 2nd GEN TACOMA.

2nd gens DO NOT HAVE A THERMOSTAT on the trans.



OP the closer to 175*f you can keep it the better. Under 205 is fine as long as you adhere to doing the trans fluid every 60k miles or so (manufacture recommended). Your pop up trailer while at the upper limit of comfortable weight to tow has the advantage of a low profile and less wind resistance vs a box trailer. As long as you keep the transmission from hunting in between 4th and 5th as well as hunting in and out of torque converter lockup in those gears you will be fine.

Easiest thing to do would be to just pop it in 4th and call it good (this keeps rpms up, transmission from hunting and thus torque converter locked up more often - which will keep temps WAY down). Keep an eye on trans temps and note: the temp you want to monitor is the pan temp not the torque converter output temp (the later will fluctuate drastically).

Now if you find on a more hilly trip you are up consistently around the 205-220 mark for PAN then yes, get a bigger cooler, but with some common sense and just awareness of what your truck is doing shifting wise you shouldnt have a problem stock.

Also, dont be afraid to use D(5th) gear if you are on a flat stretch and you can achieve 5th gear with the torque converter locked.

130k miles on my truck, bone stock trans cooler setup, multiple trips out to the dunes, various off roading slow moving trails, heavier loaded down towing (worst of which was a 4klb bigger tear drop trailer up a 4kft grade into 30mph winds) and trans temps have never gotten consistently to the point of me wanting to go to a bigger cooler.

 

I see you have one of the mobile black tank "totes" what are your thoughts? Our HW has a 12 gal black tank and we didn't even come close to filling it over the course of the 3 day trip. Also, we had the AC running all day and temps inside still got to 88degF at one point. We ordered a set of "Popup Gizmos" to "insulate" the bunk-ends and dinette slider, and are looking at getting a few rolls of reflectix to insulate the windows and under the mattresses. Any other recommendations to keep the heat down?

 

Mine doesnt have a gray/black tank, so the rolling honeypot is a necessity. I do find it very handy at some campgrounds, in that you don't have to move the trailer to empty it - it makes packing up easier. It was particularly handy at the Great Smokies NP last November. The RV dump was a good 5 miles from camp, and we were going to be pulling out in the opposite direction. It was just easier to drive the tote to the dump while the better half started folding up the dinette and taking down the linens.

That one is a 21 gallon, I have never even come close to filling it. Most weekends for us will generate 5-7 gallons of gray water, I dont think I've generated 20 in a whole week.

-

The Gizmos and reflectix are big on my to-do list this year. These things are blistering in the summer. I also use a couple of these guys to use as bunk fans:

$40 xasla 10000mAh Portable Rechargeable Clip on Fan, 8" Battery Operated Fan, 24 Hours Work Time, 4 Speeds Personal Fan, Ideal for Outdoor Camping Golf Cart Home Office Blue

https://www.amazon.com/10000mAh-Por...93?keywords=opolar+fan&qid=1648568845&sr=8-18

Those plus a small desk fan on the dinette helps that hot pocket of air reach the A/C. Once in a while I'll use the bunk curtains to close off a section and that sort-of helps keep the rest of the trailer cool(ish) during the worst of the day.

 

Does anyone here happen to know at what temperature the transmission ATF warning lamp is triggered on the cluster?

**Update: Found it right here in the Forum: 302 degrees.

https://www.tacomaworld.com/threads/transmission-max-temp-toyota-answers.279990/#:~:text=If you are towing with your vehicle, the,indicates a malfunction in the auto transmission system.

I'm considering putting a larger aux transmission cooler my truck. The current one appears to be the same width as one I had on another vehicle but was taller by 2/3rd's than the stock one. It was made by Tekonsha.

 

IF i was going to go with a bigger cooler id simply remove the stock aux cooler all together, and put one of these in its place (and keep the stock line routing - that is keep the run through the radiator)

https://www.haydenauto.com/en/produ...oil-coolers/patented-internal-by-pass-coolers

Either the 697 or 698 depending on how i wanted things to be and what the measuring tape tells me would fit better. Oriented on its side so that fluid comes in the bottom and out the top (to make it to where air doesnt get trapped and full cooler gets used).

The neat thing about these ones is they have a build in thermal bypass. When its cold the bypass is open and fluid mostly circumvents the rest of the cooler, when it heats up the bypass closes and fluid flows through the whole cooler. Less points of failure vs adding on a second cooler in tandem with the original aux, no worry of overcooling, and no need for an external inline thermostat.

 

Hayden is an excellent brand as well; same stacked-plate design which provides much more surface area than tube-and-fin designs. Re: Cooling capacity or over-cooling in the winter: things change, and it has been a while, but when I asked a transmission mechanic back then about which size I should install he said simply: "For anywhere other than the tundra, or around the Arctic Circle areas of the world: The largest one that will fit". He was of the opinion that it was nearly impossible to over-cool a transmission, especially if the factory radiator cooler remained in place; and if you were somewhere were it was an issue, you had bigger worries to deal with than a cold transmission. Made sense to me. YMMV

 

Sorta related to the topic at hand, someone reported that heat shield around the lines coming off of the transmission next to that cats had a big impact on reducing temps.

https://www.tacomaworld.com/threads/how-to-lower-your-trans-temps.736156/

$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/dp/B093CXPCVH?ie=UTF8

 

I might have to look into those. I have a regular, non-bypass Hayden cooler that I installed on my truck. It's an awesome cooler, dropped temps like crazy even on hot days, and it almost feels like the temps are TOO low most of the time (typ. hover between 130-150). That bypass would be super useful.

Also, can confirm, there is no thermostat for the trans cooler/trans lines.