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Monitoring ATF temps on Sydney-Melbourne drive

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  • Monitoring ATF temps on Sydney-Melbourne drive

    OBD2 CAN data

    OBD2 bluetooth connector (Veepeak OBDCheck BLE Bluetooth OBD II Scanner)
    Car Scanner Pro app

    Toyota Landcruiser Prado

    2010, 5 speed Automatic A750, 4.0L V6 Petrol. Car totally stock at the moment, highway tyres. Just got the car in January after 10 great years of owning a 90 series.

    • Coolant Temp
    • ATF temp v.2 (Pan Temp)
    • ATF temp v.3 (Torque Converter TC Temp)
    • Engine Oil Temp


    Sydney to Melbourne over ~9 hours. Flat driving, entirely highway except for some stops. Up to 20 degrees ambient during the day, down to about 8 degrees at night before coming into Melbourne.

    Key points:
    • Coolant temp seems to be controlled to 85 degrees regardless of the outside air temp.
    • ATF Temps v.2 (Pan) and v.3 (TC) are interesting to watch. When cruising in 5th gear, without any torque converter slip, they converge to the same temperature, somewhere between 52 and mid 60 degrees. And the absolute temperature variance may simply be about ~40 degrees above ambient temp, where the cooling system keeps it constant relative to ambient rather than at a consistent absolute temp like the Coolant Temp being kept at 85 degrees.
    • When either engine braking by changing down the gears, or accelerating up a hill, which causes torque converter slip, the v.3 temperature separates very quickly and gets ~5-8 degrees hotter than v.2 temp. While driving at a constant speed and when not getting torque converter slip, the temperatures converge again quite quickly to the v.2 temp
    • What’s interesting is when engine braking down to a stop, the v.3 stays hot while the car is stopped and can’t seem to converge back to the v.2 temp. My guess here is that the v.2 is cooled from trans oil, and the v.3 is air cooled. So when the car isn’t moving, the v.3 isn’t getting cooling.
    • Engine oil temp tracks ATF v.2 temp reasonably well. This would indicate they are sharing the same oil cooling system?
    • Another notable small effect is when engine braking, the Coolant Temp in the engine drops immediately from say 85 to 82 degrees. This must be as the engine is spun up faster without the extra fuel added in.

    Other notes:

    ~11.0L / 100km average on trip computer. On highway drives I’ve found the trip computer overestimates the fuel that is burned, and from refiling full to full gives more like 10.5L/100km. But the opposite is true for around-town driving, where the trip computer underestimates the fuel burn by about 0.5L/100km as well (around 14.5L/100km in real life, 14.0L/100km on the computer).

    Just posting as an FYI for those interested, if there are any comments or questions. It's a good baseline to see how the temps change once I start hitting some VHC tracks again.

    I am wondering - do aftermarket trans coolers have any impact on the Torque Converter Temp? As that one is the one that seems to be air cooled, and gets hotter than the Pan Temp and Engine Oil temp.


  • #2
    The V6 has a transmission cooler as standard.


    • #3
      When the torque converter is working hard (Ie slipping), its outlet temperature is 5 - 10 degrees hotter than the pan temperature. So yes, the lower you can make the temperature of the ATF in the gearbox pan, the lower the torque converter outlet temperature will be. I put a Davies Craig 678 radiator in my 2016 GX for towing and this typically lowered temperatures by 15 to 20 degrees.

      The other thing to do is to hold the gearbox in a lower gear, so the engine (and the gearbox input shaft with the torque converter) spins faster, making the TC's job easier and giving it more chance to lock. When the TC is locked it does not contribute much, if anything, to the gearbox temperature.


      • #4
        I've had a trans cooler for years because of towing and never see TC temp above about 85-90. The TC and Pan are the same oil, just measured at different locations. Anything that lowers the trans temp is good.

        I change the trans oil every 50k and despite the trans cooler it is always starting to discolour a bit. Oil is the life blood of engines and transmissions. Anything that you do to keep it clean and at the right temp has a huge impact on component life.

        There is a corollary. When I was working with heavy equipment our oil sampling found that changing engine oil too often actually introduces more wear particles. There is no technical benefit to 5k oil changes other than making you feel goods, and yes that pushes a lot of people's buttons.

        2010 Silver GXL Prado 150, D4D Auto, with a few non standard bits


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