Effect of gear selection on ATF temperature

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ROOKIE
High Range 4WD
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Real Name: PAUL
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Effect of gear selection on ATF temperature

Post by ROOKIE »

Hello All.

I thought I would share with you the results of some testing I have done in my 2012 Hilux 4.0 V6. (Please note, that I am a complete desk jockey and am open to any corrections, this was just done for personal education)

After much google-foo I eventually found some custom PID’s that work on Torque Pro that measures the ATF temperature in the Toyota A750F gearbox. This gearbox has 2 temp sensors, one in the pan and one in the torque converter. This auto gearbox locks its torque converter in 4th and 5th.

I wanted to find out how my driving style was affecting the temperature of the ATF when climbing a hill.

The test methodology was to drive the same route, with a different gear selected. As I live in Durban, the hill selected was Fields Hill that rises 200m in 3.6km. There is a speed limit of 80km/h on the hill with average speed cameras in operation. That would be useful as I would be traveling at pretty much the same speed as every one else. At the top of the hill I could exit the M13, and join it again heading back down the hill to the start of the test run.

Run1 – gearbox in D.

The first run I left the vehicle in D, keeping the speed at 80km/h.

At the bottom of the hill the vehicle was in 5th- torque converter locked and the temps at the start of the run was in the low 60’s .

Note on screen grabs. Gearbox Pan temp is top left, followed by torque converter and finally engine coolant temp.
Run 1 Before.png
As I started to climb the hill, the torque converter unlocked, but the gearbox remained in 5th. So I had torque converter slip.

At the top of the hill, the torque converter temp has climbed to a high of 63 deg to 95 deg and it had taken me 3 minutes to drive the route.
Run 1 after.png

Run 2 – 4th.

At the start of the test run, I moved the gearbox from D to 4 on the selector. The gearbox selected 4th and the torque converter locked up.

At the start of the run, the temps were now in the mid 70’s.
Run 2 before.png
Interestingly, at the top of the run, the temps were cooler, despite the engine coolant temp increasing.
Run 2 after.png
This shows the effect of a locked torque converter.

For interest I did another run for 3rd gear

Run 3 - 3rd.

Same process, but this time I moved the selector from D to 3 at the start of the run. The gearbox selected 3rd with no torque converter lock up.

Temps at the start of the run were again near the mod 70’s.
Run 3 before.png
At the end of the run the torque converter temp was in the mid 80’s.
Run 3 after .png
It is interesting that the temps are lower than run 1 despite no torque converter lock up. To my thinking this is either due to, less gearbox load due to higher engine revolutions (the engine is working harder so the gearbox does not need to OR, it is due to higher fluid flow rates (engine coolant and ATF fluid) due to higher engine revolutions).

My takeaways from this are:-

My driving style is not conducive to long term ATF / gearbox health. While the ATF temp never got dangerously hot, one must consider that I was alone, in an empty Hilux in cool ambient temperatures on tar. I suspect that driving my fully laden Hilux from De Hoop to Kokerboom Kloof, through sand in 42 deg temps the ATF got significantly warmer.

The 4.0 V6 develops enough power and torque to keep the gearbox in higher gears with torque converter slip in a quest for economy, at the expense of ATF temperature. MY driving style is such that supports that. I rarely accelerate heavily so at most when accelerating or climbing a hill, the torque converter just unlocks and the gearbox stays in a higher gear. On longer climbs, I should manually select 4th.

Gearbox temperatures only decrease when the torque converter is locked up, and that only occurs under load. When descending fields hill, with the engine running against compression in 4th, torque converter unlocked, the gearbox temperatures actually increased.

When the torque converter locks up, temperatures decrease rapidly. For example, at the end of run 1, temps were in the mid 90's, within 15 seconds of torque converter lockup, gearbox temperatures were in the min 80's and falling.

However, it must be noted, that once you have added heat to the fluid, it takes a long time for the fluid in the pan to cool down.

I trust you find these ramblings of interest.

Paul.
09 4.0 V6 Auto 4x4.
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dalkill
LR4WD, Lockers, Crawler Gears
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Re: Effect of gear selection on ATF temperature

Post by dalkill »

thanks Paul.

i have somewhere on the forum commented on my gear selection with the manual D4D, running up the hill on Sir Lowry Pass... also a fair bit of a climb on tar.

Also 80kph average speed camera.. i found in 5th the revs just touching 1500rpm which is where boost just waking up.. and i feel bakkie not in comfort zone. So i rather shift to 4th , with bit higher revs, but engine and gearbox just seems happier for it.

I often see people driving with economy in mind, and hear them change gear at like 1000rpm. To me it just seems to soon to end up at 60kph in 5th. I feel like the gearbox taking strain. DOn't know why.. but your temp figures supports my theory.
2016 2.4GD6 SR D/C 4x4 (Oct 2022 - current) (Buraaq VI)
2007 d4d 3.0 D/C 4x4 (Mar 2016 - July 2022) (Buraaq V)
2003 Isuzu KB300 D/C 4x4 (May 2015 - Feb 2016) aka Buraaq IV
2000 hilux DC 2.7 4x4 (Jul 2011 - Sep 2012) aka Buraaq III
1999 RXI 20v (Nov 2009 - Jul 2011) aka Quicksilver
1990 hilux DC 2.2 4x4 (Jun 2008 - Jul 2011) aka Buraaq II
1997 corolla 160i GLE (Feb 2007 - Sep 2009) aka Green Goblin
1990 GLI twincam (still my fav rolla) (Oct 2005 - Mar 2007) aka Wit Blitz
Golf GTI 2.0 (temp insanity for 2months) (Jun 2005 - Aug 2005) aka A mistake
1993 hilux SC 2.2 4x4 (April 2003 - Sept 2005) aka Buraaq

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