I think klrogers right i remember reading somewhere there is a check engine light for failed thermostat. The computer uses ambient temperature and engine load to estimate how long the engine should take to warm up. If it takes longer than that the check engine light may turn on.
if you can hack in a prius radiator and a small pump. The prius radiator supports 2 coolant loops as the electronics are suppose to run at a cooler temperature. maybe you can use the second loop to cool your CVT?