cooling air flow over the supplemental heat exchanger in the fig3 embodiment a transmission 38 is also shown an auxiliary coolant radiator 40 is provided the auxiliary coolant radiator 40 is connected via a conduit 42 to an auxiliary cooling pump 44 an expansion tank 45 is coupled with the conduit 42 via a further conduit 46 the auxiliary pump 44 is coupled to an auxiliary heat exchanger 48 via a conduit 50 in the embodiment of fig3 oil is routed from the flow control valve 32 through the conduit 28 u2032 to the auxiliary heat exchanger 48 and then via a return conduit 30 u2032 to the pan 16 a conduit 52 couples the transmission 38 to a temperature responsive control valve 54 when the temperature of transmission oil exceeds a predetermined temperature the flow control valve 54 will open and transmission oil will flow via the conduit 52 the flow control valve 54 and then via a conduit 55 to the auxiliary heat exchanger 48 return flow of transmission oil from the auxiliary heat exchanger 48 is via a conduit 56 in so far as engine lubricant cooling is concerned the system of fig3 is the same of that of fig1 and 2 except that a liquid to liquid heat exchanger 48 has been substituted for an oil to air heat exchanger 26 and an auxiliary radiator 40 has been provided in addition cooling of transmission lubricant via the auxiliary heat exchanger 48 is provided it is well within the scope of this invention to provide a coupling of transmission oil to an oil to air heat exchanger in lieu of a liquid to liquid heat exchanger 48 in addition individual transmission and engine lubricant heat exchangers rather than the joint heat exchanger 48 of.