From a 1938 Dodge truck shop manual ; Under Engine Temperature , In instances where the service of the truck requires frequent stops such as door to door delivery , it is recommended that the engine be operated at a higher temperature . This may be accomplished by using a thermostat which opens at a higher temperature or by using a partial cover over the radiator grill , in order to reduce condensation in the crankcase sufficiently . And in a prior paragraph it mentions the forward travel of the truck drawing fresh air into the breather pipe and out of the ventilator pipe . It also lists three types of anti freeze , denatured alcohol , methanol , and ethylene glycol .