They say ignorance is bliss, and sometimes not knowing what's going on inside your gearbox seems nice. Afterall the manufacturer has spend millions of dollars researching, designing and testing to get it perfect right? This all seemed logical to me most of the time but a couple of things have recently made me question this thinking.
Firstly, when driving in thick sand or towing my caravan up hill for hours on end I have really noticed the heat coming through the floor. Even though there are layers of metal, insulation, carpet and footwear, my left foot begins to sweat in my shoe. At first I think about how uncomfortable this is but eventually I start to wonder how my car feels about this.
Secondly, I recently setup an OBD2 scanner so I could monitor how my DPF system is performing, but as a by-product I was also able to see what the actual transmission temperatures were. I discovered that they regularly sit at around 120 degrees while towing and from what I have read this is considered in a range that will significantly reduce the life of the transmission fluid and maybe even the seals or gearbox components.
From some basic research it becomes more obvious that the manufacturer does have to make some difficult compromises in the design. A setup could be focussed on any aspect of being smooth, quiet, responsive, fuel efficient, tuned for city, highway, off-road or towing use. If you look at the most common customer who buys your model, and what they do with it, that is probably who and what it is tuned for. So maybe there is something to the idea that you can further fine tune for your particular use too.
It appears there are three main solutions to high transmission temperatures: (1) drive in a lower gear, (2) add a transmission cooler, or (3) fit a lockup kit.
Driving in a lower gear is what many manufacturers recommend. It is also the easiest solution. However, you also need to be willing to put up with the noise and vibration of running your engine and transmission at higher revs. If you purchased your vehicle because of its smoothness and quietness this is going to be disappointing. You will need to use your gearbox sports mode to select the maximum gear.
A transmission cooler is an additional radiator that your automatic transmission can cycle it's fluid through to improve the cooling effect on the fluid. This can typically reduce the overall fluid temperature by 20 to 30 degrees. This is a relatively low-tech solution and basically amounts to adding a couple of longer hoses, the small radiator itself and a few screw clamps. The hardest parts are finding the best place to mount the radiator, run the hoses, and ensure the fluid level is right. Specific kits for your model will make this very easy and start from prices around $250.
An automatic transmission lockup kit will actually address the root cause of high temperature generation, the slippage of the transmission's torque converter. It hooks into the control electronics to reduce slippage by locking the torque converter more often. These units can generally be switched on and off as required and are arguably a solution that manufacturers should fit as standard. Perhaps the scariest part of this solution is the fact that wires to the vehicles ECU need to be cut and resoldered. Lockup kits generally start around $500 plus installation. A welcome by-product of this solution is that you can also get a significant improvement to your fuel economy.