Overheating Transmission

[Bad1975]

Edited original post, the iforce max architecture is identical whether 8 speed or 10 speed and does have a TC along with K0 clutch and friction clutch and damper on the engine flywheel, good video explaining it all here.

The additional issue here is you have two potential sources of major heat generation, the TC and the K0 clutch working against transmission fluid temps if not properly designed for cooling capacity and or optimized shift points along with when to change between hybrid drive, charging the batteries and ICE only it becomes quite complex to manage and optimize the transmission fluid temp for all scenarios, this is probably one of the reasons the manual says to use 4L, the vehicle has no way to know whether or not you're offroad since it's a full-time 4WD setup and therefore no way to know it should change its behavior if capable of doing so unless selecting 4L?

Hopefully Toyota offers some changes in the software/firmware to correct these temp issues. Still want to know if the OTT which modifies shift behavior has any benefit toward reduced fluid temps?

 

[whyzee125]

While trying to find diagram of the torque transfer i found this interesting analysis. Answers many questions we have regarding abrupt shifting behavior.

Toyota L580F Transmission Guide: Reliability, Problems, Repair Costs

The L580F is where Toyota’s modern truck-hybrid transmission story gets complicated in ways older Toyota truck automatics never were.

transmissionaudit.com

I can find the 10spd hybrid L4A0E.L4A0F diagram and it shows engine->K0->TC->transmission
Cant find this for LC250 L580F, i thought it was the same as 10spd layout.
Here is the source of 10spd layout. Appears to be same for 8spd but cant confirm.

Toyota Hybrid - Transmissions line-up

List of hybrid transmissions of Toyota and Lexus vehicles

toyota-club.net

That transmission audit article is the most ChatGPT-sounding thing I've read in a while. I looked through his other stuff and it's very obvious it's all AI-written, but some of the points are still worth considering.

It seems like most manufacturers have some growing pains when implementing a new drivetrain or philosophy (ie going from NA to turbo engines, etc.). Hopefully Toyota will figure out a way to mitigate this, either through better OEM cooling, slightly updated trans, or more likely new software to keep the TC locked when off roading.

 

[ultane]

That guy is the best at expelling the hybrid system!!!

 

[Yousef]

Edited original post, the iforce max architecture is identical whether 8 speed or 10 speed and does have a TC along with K0 clutch and friction clutch and damper on the engine flywheel, good video explaining it all here.

The additional issue here is you have two potential sources of major heat generation, the TC and the K0 clutch working against transmission fluid temps if not properly designed for cooling capacity and or optimized shift points along with when to change between hybrid drive, charging the batteries and ICE only it becomes quite complex to manage and optimize the transmission fluid temp for all scenarios, this is probably one of the reasons the manual says to use 4L, the vehicle has no way to know whether or not you're offroad since it's a full-time 4WD setup and therefore no way to know it should change its behavior if capable of doing so unless selecting 4L?

Hopefully Toyota offers some changes in the software/firmware to correct these temp issues. Still want to know if the OTT which modifies shift behavior has any benefit toward reduced fluid temps?

This issue has nothing to do with the hybrid system as the overheating issues are also present on the non hybrid petrol and diesel variants.

I believe it's designed to run on the hotter side maybe for fuel economy or other unknown to us reasons .

Toyota should've added a small trans cooler similar to the ones available aftermarket and that will solve this issue completely as per my experience with the one I installed.

 

[grandsons]

This issue has nothing to do with the hybrid system as the overheating issues are also present on the non hybrid petrol and diesel variants.

I have a feeling possibly biased that in Europe, where diesel variants were quite common, there are fewer issues. This might be because the LC250 tends to be less modified there in terms of wheel size (in Europe, wheel diameter mods are generally limited to about ±5%) and weight (fewer accessories fitted).


Personally, without towing, I've noticed the gearbox running hot on some steep, high-elevation gravel roads in hot Greek summer conditions (five peoples+ luggages on board). It seems to rise quite quickly at 108-110°C and take ages to cool down.

I don't understand why, but the torque converter's behavior seems inconsistent sometimes it locks up or the transmission downshifts, and other times it doesn't. I've never figured out the logic behind it. In some cases the converter seems to let the torque converter slip instead of downshifting, while in other situations it downshifts right away. I also ignore the thermal influence of a converter slipage.

I noticed the slipage when using a Scangauge, because the converter slip may sound exactly like a downshiting.