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Discussion Starter · #1 · (Edited)
The last 4 days I recorded a series of logs while towing my 7000lb TT using OBD Fusion but I'm having trouble finding them. The logs created appear to be locations, not ATF1 (sump), ATF2 (converter), air temp and coolant temp as I thought I was recording.

Anyway, here are my observations;

75 degree air temp.
Coolant temp never rose above 190, it mostly held at 185.
Tow/Haul on at all times when towing

Test 1 = Drive mode, Cruise set to 68, would shift between 4th and 5th. ATF sump and converter temps held between 210-215 consistently.

Test 2 - S mode 4th gear (my fav), cruise set to 68. ATF and converter hardly moved from 210.

Test 3 - Drive mode, MANUAL throttle control, held speed at 68, same ATF temps as above.

Test 4 - Drive mode, tried to hold low RPM as so many do allowing speed to drop on hills while trying to hold back downshifts. ATF sump held around 210-215 but ATF converter jumped to 260. Once the lugging stopped or it downshifted, the temp went down. Clearly, this mode of operation is the worst option.


Regular driving, not towing; Interstate travel @ 80mph ATF temps of 150-180 are common. City driving, 190-205 are common.

I encourage people to try this on their own. The app is cheap and seemingly accurate until proven otherwise.
 

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Observations:

Your interstate travel ATF temperatures towing 7K are about the same as mine loaded lightly. Your ATF temperatures in regular interstate driving are way lower than mine.

Your coolant temperature towing 7K seems about 10 deg cooler than mine loaded lightly.

Clearly your setup is doing a better job of cooling than mine. Things I may try:

1) Put an aluminum heat shield between the passenger-side exhaust pipe and the coolant-to-ATF heat exchanger. (On my rig they are separated by about a 3/4" air gap with no heat shield.)
2) Install auxiliary ATF cooler.

A side note: Of course its a great idea to have tow/haul on as a default when towing. You're probably aware of this, but when using S mode, tow/haul doesn't do anything different:

During tow/haul control, the ECM controls the engine output, transmission shift schedule and shift timing
to ensure drivability when a trailer is towed. The tow/haul control includes a throttle control, shift schedule
control, wide open throttle shift timing control and AI-SHIFT control.
 The conditions required for tow/haul control to operate are as follows:
- Shift position: D position (Tow/haul control does not operate in the S position).
- TOW/HAUL pattern select switch: ON
 The TOW/HAUL indicator light is used to inform the driver that tow/haul control is operating.
 

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Discussion Starter · #5 ·
Observations:

Your coolant temperature towing 7K seems about 10 deg cooler than mine loaded lightly.


A side note: Of course its a great idea to have tow/haul on as a default when towing. You're probably aware of this, but when using S mode, tow/haul doesn't do anything different:
Might be my air temp was lower? While I do not know my ATF temps during my trip out West with temps as high as 121, I do know my coolant was running 210 consistently while towing. The highest recorded (and I was not running the Torque app at the time very often cause I really wanted to see ATF temps and it was not working...so I turned it off most of the trip)

I know the manual says Tow/Haul doesn't do anything in S mode, but I only use it when on the Interstate at a constant speed and RPM. I use drive mode for all other periods. (And may be its in my head, but throttle response with T/H on and D vs S sure feels the same!)
 

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Might be my air temp was lower? While I do not know my ATF temps during my trip out West with temps as high as 121, I do know my coolant was running 210 consistently while towing. The highest recorded (and I was not running the Torque app at the time very often cause I really wanted to see ATF temps and it was not working...so I turned it off most of the trip)

I know the manual says Tow/Haul doesn't do anything in S mode, but I only use it when on the Interstate at a constant speed and RPM. I use drive mode for all other periods. (And may be its in my head, but throttle response with T/H on and D vs S sure feels the same!)
Good points. My test was at a higher outside temperature, 85 or maybe even 90 if I remember correctly.

I think we are on the same page. I like D with tow/haul for better shift points when accelerating up the onramp and merging into traffic, then S mode while cruising.
 

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Observations:

Your interstate travel ATF temperatures towing 7K are about the same as mine loaded lightly. Your ATF temperatures in regular interstate driving are way lower than mine.

Your coolant temperature towing 7K seems about 10 deg cooler than mine loaded lightly.

Clearly your setup is doing a better job of cooling than mine. Things I may try:

1) Put an aluminum heat shield between the passenger-side exhaust pipe and the coolant-to-ATF heat exchanger. (On my rig they are separated by about a 3/4" air gap with no heat shield.)
2) Install auxiliary ATF cooler.

A side note: Of course its a great idea to have tow/haul on as a default when towing. You're probably aware of this, but when using S mode, tow/haul doesn't do anything different:
Pretty sure this is model-year dependent. My 2016 manual doesn't mention S vs. D when TOW/HAUL is activated, and the truck absolutely feels like TOW/HAUL is working in S-mode. I also thought I read in a Toyota document that it works in both modes, could have been on a forum I guess.
 

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Pretty sure this is model-year dependent. My 2016 manual doesn't mention S vs. D when TOW/HAUL is activated, and the truck absolutely feels like TOW/HAUL is working in S-mode. I also thought I read in a Toyota document that it works in both modes, could have been on a forum I guess.
That may be the case. The quote I gave was, I believe, from a 2007 document when the 6-speed transmission first went into production. Since tow/haul mode operation seems to be implemented purely through software, it is possible that the software was upgraded some time later to implement tow/haul operation while in S-mode.

Here is a good way to tell if tow/haul is operational. On my truck when I'm lugging up a hill in D-6, I hit the tow/haul button to force a downshift. The transmission instantly downshifts to D-5 when the tow/haul light comes on. I need to try activating tow/haul when lugging up a hill in S-6 and see whether or not it results in a downshift. Might be interesting to compile results of this test by model and year.
 
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