1. A control system for a vehicle equipped with a drive system including an internal combustion engine driving an infinitely variable ratio transmission, said control system comprising, in combination: A. a manually operated throttle for generating engine speed commands to the engine; B. a first sensor for generating a signal indicative of engine speed; C. a transmission controller operatively linked with the transmission, said transmission controller adjusting the transmission ratio in response to said engine speed commands and said engine speed signal to maintain an engine speed schedule corresponding to a given engine speed command; D. a temperature sensor monitoring the heat rejected by the drive system, said controller operating in response to said temperature sensor to produce a decrease in engine speed by increasing the transmission ratio when the heat rejected by said drive system reaches an unsafe level and then adjust the transmission ratio to maintain the decrease engine speed as a new engine speed schedule for said given engine speed command.