Questions on S mode and Towing

I had a 2016 with an auto I bought to tow my boat. After reading posts on here I towed in S5. As I remember, I finally read the manual and combined with real world experience became skeptical of the claims of not towing in D. In this world of computer controlled engines and transmissions, I’m skeptical that Toyota would put a transmission in a pickup that would grenade due to being driven in D while towing.

One question in my mind is why they didn’t program the transmission to automatically downshift during long descents. They chose to leave that up to the driver.

 

Them hills are calling….

 

You know, what I can’t confirm if it doesn’t downshift or not, I’m always premeditating and doing it manually.

I think it does though, I remember there’s one certain hill I used to drive down in D (never towed down it) and it would always kick down a gear and I would have to go to S mode and force it back to 6th.

Is this a confirmed thing no downshift? I’m gonna have to try this next time out…

 

I tow with my scan gauge to monitor temps, and in my experience tow in s mode keeps the trans temp much lower by limiting the number of shifts taking place. The trans really builds heat if its "gear hunting" on hills and can exceed 200 degrees, the danger zone for atf, quite quickly. Towing in s mode and just picking a gear to stay in keeps it much closer to 170/180 degrees.

 

Thank you all for the feedback and information. I will experiment with these suggestions and relay my experiences back to the thread. Based on what I’ve read I think I will play it safe and use S mode and see how the truck feels in either S4 or S5 once it’s under weight and likely have ECT on. If I hit any hills/descents I’ll keep it in the S4 range or lower if needed.

 

I looked all over for specs on Toyota transmission heat range and found very beyond FUD being sold by sellers of transmission fluid and transmission coolers. Technology has changed. Is it possible that your assumptions of good transmission temps are an anachronism?

 

Tons of great info here. Push that ECT button whilst in Sport mode and let your mind wander to your destination.

 

It downshifts if you slow down as I remember, but not while descending and not enough to cause significant engine braking. ECT seemed a little more aggressive in my memory.

 

200 is not danger zone, that’s only like 10 degrees over when the thermostat opens at 190.

Today I drove over a mountain pass with wife and dog in the car and trans temps hit 219 degees. This was driving ECT on in s4 (not towing) at 45 mph following traffic (ie not racing). I did gain 2,600ft in 7 miles so it was an extreme climb.

Cruising in D at 60mph on flat tc trans oil temp sits at 187/190 degrees.

 

Ahh okay, that makes sense!

 

Transmission fluid breaks down much quicker when you get passed 200 degrees, this is a well know fact, it won't destroy your tranny but fluid life is effected. @gearcruncher has alot to say about it. Transmission fluid is not indestructible and the fact that toyota says you don't even need to change it shows they care more about replacing trannies, then they do about accurate data on trans tamps.

 

Its pretty well established that transmission fluid breaks down very quickly once it gets above 200 degrees, the thermostat opening at 180 degrees is to improve gas mileage, not to preserve the life of the fluid.

 

Great info here all. Wish more people understood engine braking via the transmission. Steep grades where I live. Rule of thumb for fully loaded semi drivers. The gear you went up in is the gear you go down in. Applies to towing with regular trucks as well to some degree. I love S mode. I use it in the city and while going through steep mountain highway passes. I even use engine braking going down steep grades fully loaded with just the entire family and all our gear in the back. No trailer. In the city I mainly chug along in D. However if I get annoyed and need to drive more aggressively I'll use S mode to keep the RPM'S up to move more quickly.

 

I’ve read a lot about transmission fluid degradation due to heat, but near zilch about Toyota replacing transmissions.

 

I changed my post, thermostat opens at 190. Why would Toyota run the risk of ruining the quality of the oil by allowing temps to run well above 200? And even on top of that then remove the dedicated trans cooler to allow temps to run potentially even higher?

 

Maybe their engineers know more than us.

 

They care more about mpg numbers than they do about transmission life, they wouldn't have made a "sealed" non serviceable transmission if they cared about transmission life. MPGs sell cars, not the transmission fluid life.

 

You seem to be ignoring Toyota’s highly prized reputation for quality.

 

You think the taco has good mpg rating?

Hilux with a turbo diesel has good mpg ratings.

I’ll try and find out if they use the same trans…