The reason we've elected to go with an oil cooler rather than larger heat exchangers is due to the reason that unlike an internal combustion engine, there are two systems on the Model 3 with slightly different operating temperatures. The battery really needs inlet coolant temperature in the 25-30C range, and the Drive Unit can accept inlet temps in the 35-50C range.
Tesla already has a method of keeping the two systems separate - when the AC Compressor is running and the system is in Parallel mode, the AC Compressor can focus on removing heat out of the battery.
The oil is the hottest fluid, so using an oil cooler with fans allows a direct interface with the hottest fluid to the air. It is also the simplest to install. Any heat that is removed from the oil cooler is heat that is not going into the heat exchanger - so that means cooler loop temperatures and reduced temperature into the battery when the system goes into series mode.
The fan can also be independently controlled, so to Mash's point if you are concerned with heating the battery quickly for supercharging, not running the fan will result in simply a little bit more thermal mass in the oil system, but not a significant delay in heating the system (this is something I know for sure as we tested supercharging and there was no issue for the battery loop to get up to temperature for supercharging).
So all in all, pulling out a ton of heat with oil coolers seems like the logical way to go.
Beyond that certainly, a more hardcore approach would be a larger AC condenser, chiller, and radiator.
However since the system is so complex, and Tesla has multiple different ways of doing the control systems, it's harder to make a perfect back to back comparison. What I can say is that when we disconnected the AC Compressor from our RWD car, without the oil cooler the drive unit overheated in 2 laps. With the oil cooler it didn't overheat for over 15 minutes.
You can put your hand behind the fan and feel the amount of heat coming out of that thing when the Oil Temperature is 70 degrees C!
Here's an overlay from some road testing we did on our LR RWD. The testing consisted of full-throttle power pulses from 60-110km/h. The stator temperature is down 8degC, the oil temp is down 2degC - but the big difference is that the powertrain and battery loops are down 2.4 and 1.3degC respectively - because the oil cooler is working in parallel with the existing heat exchanger. You can also see the significantly different slope of the rear oil temperature.
The colored traces are without the oil cooler, and the white traces are with the oil cooler.
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