Abstract: An oil cooler control for the cooling of lubricating oil especially advantageous for engines of relatively low horsepower operating at relatively high R.P.M. makes use of a thermal responsive bypass valve device for altering the path of oil circulation over a cooling coil. The valve device has a valve chamber with a valve seat intermediate opposite ends and a valve element cooperates with the seat in response to a thermal drive element. When the oil is cool most of the oil is passed from the engine through the chamber and directly back to the engine. As the oil temperature increases the valve element is seated causing the oil to be passed through a cooling coil and then back to the engine.