Like others here I was running into issues with the T4 controller in my 2013 e6S overheating intermittently. Given all the upgrades (D&D motor, high voltage lithium, 17" wheels, 10.35 gears) and residing in south Florida it’s to be expected I suppose. I was planning to first clean and reapply the thermal paste between the controller and the frame but after removing the controller and seeing that there wasn’t much contact surface I didn’t bother applying new paste and starting looking into adding a heatsink. I followed the recommendation of others on here and sourced the aluminum heatsink from HeatsinkUSA. They offer many sizes and there are three sizes that would work well for this controller. I went with the biggest size mainly because the fins would be open to the front of the vehicle and I figured that would be best for optimal airflow. My goal was to avoid adding fans just to keep things simple.
To install the heatsink I removed the controller housing and drilled and tapped four screws to mount the heatsink to the base of the controller with thermal paste in between. With the controller housing back on I drilled the six factory mounting holes which aligned nicely with the valleys of the heatsink. To mount the controller to the car I used threaded couplers on the factory threaded posts then added pieces of threaded rod to extend the factory mounts with nuts to bolt the controller down. Rather than bend or drill the fins to accommodate the couplers and allow the heatsink to rest on the frame I kept the assembly suspended and wedged on the couplers for additional airflow. If things loosen up over time and start to rattle I’ll consider lowering the assembly to the frame. Last, I needed to extend one field wire by a few inches, the rest of the wiring was fine.
I’m happy to report that after a few rides that in the past may have tripped an overheated controller condition the new heatsink seems to be doing the trick. I haven’t seen those errors since the upgrade. If you are running into overheating issues I’d highly recommend adding a heatsink to your controller (the sooner the better).