I have a 1930 Model A with a remachined "B" Police Head. I use a 160 degree thermostat and the car runs GREAT!! On a recent trip to Vermont and back mid-80's summer weather (360 miles round trip) the car ran consistently at 160. On long hill pulls the temp would go to 165-170; on the downhill side it would drop to 150-155 ; gas mileage in excess of 20 MPG. If the radiator is sound, a thermostat is the way to go. Just because Henry did not use it does not mean that it's use would not be an improvement in efficiency!