Internal Combustion Engine Cooling - Air-cooling

Air-cooling

Cars and trucks using direct air cooling (without an intermediate liquid) were built over a long period from the very beginning and ending with a small and generally unrecognized technical change. Before World War II, water-cooled cars and trucks routinely overheated while climbing mountain roads, creating geysers of boiling cooling water. This was considered normal, and at the time, most noted mountain roads had auto repair shops to minister to overheating engines.

ACS (Auto Club Suisse) maintains historical monuments to that era on the Susten Pass where two radiator refill stations remain (See a picture here). These have instructions on a cast metal plaque and a spherical bottom watering can hanging next to a water spigot. The spherical bottom was intended to keep it from being set down and, therefore, be useless around the house, in spite of which it was stolen, as the picture shows.

During that period, European firms such as Magirus-Deutz built air-cooled diesel trucks, Porsche built air-cooled farm tractors, and Volkswagen became famous with air-cooled passenger cars. In the USA, Franklin built air-cooled engines. The Czechoslovakia based company Tatra is known for their big size air-cooled V8 car engines, Tatra engineer Julius Mackerle published a book on it. Air-cooled engines are better adapted to extremely cold and hot environmental weather temperatures, you can see air-cooled engines starting and running in freezing conditions that stuck water-cooled engines and continue working when water-cooled ones start producing steam jets. Also the possibility of working at higher temperatures air-cooled engines have may be an advantage from a thermodynamic point of view. The worst problem met in air-cooled aircraft engines was the so-called "Shock cooling", when the airplane entered in a dive after climbing or levelled flight with throttle opened, with the engine under no-load while the airplane dives generating less heat, and the flow of air that cools the engine is increased, a catastrophic engine failure may result as different parts of engine have different temperatures, and thus different thermal expansions. In such conditions, the engine may get stuck, and any sudden change or imbalance in the relation between heat produced by the engine and heat dissipated by cooling may result in an increased wear of engine, as a consequence also of thermal dilatation differences between parts of engine, liquid cooled engines having more stable and uniform working temperatures.