The paper suggests the benefits to be gained from using an electronic thermostat to improve control over the coolant temperature of an operating gasoline engine. It also describes the work undertaken to confirm that engine temperature can be maintained at a selected level and that the temperature level can be raised or lowered as desired in a running vehicle.The common automotive mechanical thermostat has the limitation of a fixed operating point with coolant flow rate dependent on temperature rise. Over its long life it has been refined economically to the point where the advantages of a more sophisticated device, made possible with electronics, have not been explored in depth. Recent electronic advances, however, make possible the addition of features that should justify the economic differential.The advantages and features that can be obtained with an electronic thermostat will be presented along with design considerations and test results. Some of the potential advantages are the ability to incorporate existing engine electronic sensor outputs such as H.A.P., engine R.P.M., and ambient temperature into the valve control logic which can be used along with ignition timing to optimize engine performance. Engine temperature can be modified during cruise, city driving or heavy load conditions and may be used to optimize fuel economy, emissions and torque.Design considerations include both the electro-mechanical construction and the algorithms for programming the system. Test results are presented comparing the mechanical and electronic versions regarding engine warm-up and maintaining the selected coolant temperature level under changing driving conditions.