Cooler thermostats were a hot rodders trick with carburetor engines. Since the fuel was fixed with carb jets, running cooler made a leaner mixture and made more power. Running a cooler thermostat on a fuel injected car is not good idea. The fuel injection runs on sensors and runs richer when the coolant temp is lower as it is still in the warm up map. Also running the engine cooler, does not allow the fuel in the crankcase to flash off and can degrade the oil faster.
