Auto. Transmission Temperature Parameters When Towing

We're looking forward to towing our deck boat with our new to us 2016 Tacoma SR5 this summer. The Taco has 35,000 miles on the clock. Since my wife will be pulling the boat a good share of the time I'm inclined to get a ScanGuage II or something equivalent for her to monitor the trans. fluid temps. I've used a SGII for several years on a Ford F-250 and the SBII meets our needs quite well but I'm curious as to whether there is a better system than the SGII available these days.

The other question is what are the acceptable trans. fluid temperature parameters. Our boat isn't large enough (less than 5,000 lbs.) to be too taxing for the Taco, which has the factory tow package. Obviously we don't want to get into a situation where damage could result from excessive heat in the fluid. Is there an aftermarket cooler system available that can be installed for peace of mind?

 

If you have the tow package, you should have a factory cooler. Even though it's a bit anemic. Ive seen temps as high as 240* with no load, which imo, is too high. I added a mishimoto cooler with a fan in lieu of the factory cooler.

 

My only frame of reference is our 2009 F-250. We tow a 28' 5th wheel camper that weighs approximately 8000 lbs. and on a 95° F day the highest temp. I've ever seen the TFT in the F-250 is 188° F. If the TFT of our Tacoma goes to 200°+ it will get my undivided attention, for sure.

 

In my experience, you can pretty much guarantee it, even unloaded.

 

Is there any guidelines from Toyota as what temp. transmission damage begins to take place?

 

Depends on what philosophy you want to adopt. There's nothing official from toyoter afaik, but you can look up oil degradation temps, it seems pretty unanimous. If u wanna truly enter the rabbit hole, go to the Google, and type "transmission temperature gearcruncher". That should get you started. Then you'll learn new terms, new functions of toyta and lead to more Google search queries.

 

The 3rd gen AT has a thermostat that opens at 190 for the Transmission fluid to the cooler. You can pin it open. I did this and run it like this all the time. Temps hover around 165 now. Before they were 190-205 constantly. These are Unloaded temps.

 

Even in cold ambient temps unloaded I see 200 occasionally. Even with a large aftermarket cooler. I don’t pin the tstat and still run the fluid through the tank inside the radiator. I’m hoping that the temps stay reasonable towing this summer. Scanguage is great.

 

Here is what you need to know with trans Temps.

Tranmission has a thermostat for a reason, colder trans fluid isn't beneficial once you get below a certain point. Instead the trans can't reach operating temp. The issues are very apparent in higher mileage transmissions, sluggish shifting, harder shifting and so on.

No reason you can't pin in during the warm months, towing etc. But if you get actual winters, unpin it during the winter. I spent much of my auto tech career in a transmission shop. Heat is the worst, but not letting it get near temp can cause early wear issues.

 

You seem to know a few things but I got to ask...
Why did you buy a little truck to tow a load near it's limit? F250 is a great tow vehicle, it's built to tow. Even though Tacoma has a tow package it's really not built to tow more than a utility trail or ski doos.
Sure, a few people here successfully tow a small travel trailer with the Tacoma but there are much better options out there. The Tacoma is a good truck and it does lots of things well. But towing near the limit is not one of them. I did it many times and eventually traded to a 1/2 ton.

 

T stat pinned open. This is my unloaded morning commute. 50 degrees outside this morning in CA so really mild not cold. 5.5 mi commute. 11 min drive very short. I let the truck warm up for 5-10min in the morning before taking off. I’d say she gets up to safe operating temps very well and quickly in my area with the T stat pinned.

 

Have you compared oil temp to AT temp on your scangauge? I find that the pan temp is usually within 2 degrees of oil temp. I think the reservoir in the radiator does this. So given your AT fluid is going through this reservoir I can’t understand why so many are posting such low AT temps? Is the oil temp also low?

 

I understand what you are saying but our Tacoma is certified to tow 6800 lbs. I will be towing a trailer that is at least a ton under the Tacoma's tow weight certification and has little to no wind resistance. Possibly I am expecting way too much from the truck but I would not comprehend those numbers to be "near it's limit". We towed the trailer unit in question many, many miles with a 2006 Ford Ranger 4X4 extended cab with tow package and with no engine oil or trans. fluid cooler modifications. The Ranger was certified to tow 5500 lbs. and it handled it flawlessly until we sold it with 150,000 miles on it. Personally we consider the Tacoma to be a better engineered and more durable vehicle than the Ranger and the purchase price would certainly indicate that to be true. Possibly I'm mistaken.

 

That chart is based on transmission fluid at that temp for one hour.

from bobistheoilguy website

Those charts are somewhat misleading because they illustrate oil life at a constant temp.... BUT.... your actual trans temp is never constant. The basic rule is that it's time at temp that kills the oil, so based on temps alone, it's very difficult to plot in such a black and white fashion when the temps are constantly changing. The temp numbers change seasonally as well as by load, driving style, etc. I can monitor trans temp on my Ford truck in three places (cooler oil pan and valve body) and have had gauge setups on a couple of other trucks over the past 20 years as well. The cooler out line can be 225 while the converter is unlocked but the pan is still at 160F. The converter locks up and the cooler out line drops to 180. It takes a while to heat the trans up, too, so on short hops, you may never even reach 140F. If you had a computer that could plot all the high spots as you drove, I image you could predict fluid life by that but other wise, IMO, those charts are a rough guideline at best. Given the minimal filtration most trannies have, I worry more about that. Most tranny fluids will (or should) be condemned for it's contaminant load long before it would be condemned for oxidation. That statement is backed up by some 25 year long studies on trans fluids by a couple of engineers named Eleftherakis and Khalil (google them).

 

i have before i started pinning the Trans T stat. I'm trying to remember, but i could've swore that the Oil and AT temps were very similair within a few degree's of eachother often. I'll check it on my short commute and post up on the drive home tonight and again on a much longer drive this weekend. The above image is no where near fully operating temps just to show that it does still warm up fairly reasonably in my area atleast with the T stat open.

The reason i started pinning the T open is because i tow a small snowmobile trailer up into the sierra's every weekend weight approx 1300lbs loaded. I was seeing temps climb up into 220 range on some grades. Last week I did the exact same tow, but with the T stat pinned and never saw my Temps go over 170. It makes a very big difference in cooling the fluid in my opinion.

 

I towed our travel trailer last summer and highest I saw was 228 at TQ for about 30 seconds. Trailer is 5100 lbs. outside temp was 85.

 

Since we've only owned our Tacoma for a month I'm somewhat inexperienced regarding some of the nuances of it. Is there a downside to pinning the trans. Tstat open and is it particularly difficult from a knowhow standpoint?

 

https://www.tacomaworld.com/threads...ith-many-pictures.526283/page-7#post-25091163 Check this out. Lots of info for you!

 

Nice! I noticed my Trans temps really like to start climbing if I have to kick down to 3rd gear on a grade but stay cooler if I lug it in 4th. I'm running 5.29 gears and Tow a TT in the Summer months. mines only about 3800lbs fully loaded, but I'm going to start Keeping the T stat pinned so i can compare temps to what i was seeing. I did one tow last year SUPER loaded down with 2 dual sports, generator and lots of gear in the bed and a fully loaded trailer. I saw it hit 235 for about 15 seconds going up a windy slow grade but once i got it back up to 4th gear it cooled down quick.

 

like others have stated it, the downside is the AT not getting up to operating Temp as fast. Here in CA temps are very mild even in winter. Although up in the Sierra’s can reach down into the teens at times. If you live in a cold environment snow etc. I’d say don’t leave it all the time or let it warm up a bunch every cold start. It’s not that hard to pin it before each tow if you wanted to just do that, but I’m gonna leave mine pinned for now and just remember to warm it up for 5min each cold start.