Why the Air Cooled Engine Disappeared
Why The Air cooled Engine Is No Longer Greatly Used In Automotive Manufacture
The automotive air cooled engine didn't disappear. It just went underground, and that only recently. Small aircraft and motorcycles continue to use the air cooled piston engine to great effect. The most produced automobile in Earth's history as of this writing was air cooled to the very end. Wikipedia reports that 21.5 million VW Beetles were produced between 1938 and 2003, though other sources report the totals as high as 5.3 billion. The same wiki fails to mention the existence of the air cooled horizontally opposed four cylinder engine, even though it knows of the car that made it famous. Just about as many trucks (busses, pickups, and kombis) were made, and another million or so Type 3's (Notchback, Fastback, and Squareback) were produced, all with air cooled engines. A few Type 4 VW's made, and that engine also used in the Kombi. VW was the first to manufacture an electronic fuel injection system on the Type 3 and later, the Beetle and Bus. Several companies other than Volkswagen used the air cooled engine to great effect in automobiles, such as the Chevrolet Corvair, Fiat, and Subaru. The least powerful air cooled engine was found in the 1950 VW Transporter, commonly known as the Bus or Kombi, with a whopping 25 horsepower. This, in a one ton rated truck! One of the most powerful air cooled engines produced was the 1998 Porsche 993 with 450 horsepower. It is relatively easy to extract 200 reliable horsepower from a four cylinder air cooled Volkswagen engine of 1960s vintage. Several after market companies manufacture everything needed to build any turnkey engine, from mild to wild, and literature abounds to help the novice or the expert construct their engine.
Why, then, is the air cooled engine held in such disdain and no longer used in automotive manufacture? There are several reasons, but first we should look into the operating parameters of this ungainly creature, and then we can examine its retirement.
The first engines invented were air cooled. It was quickly realized that more was needed to keep the engines within optimum operating temperatures. Oil cooling was added. While monsters like the Porsche 993 use upwards of 10 quarts of oil (twice as much as large diesel engined pickups), the venerable Beetle used a measly two and half quarts of oil in stock configuration. Thermostats were also added, one to control when the oil, after reaching operating temperature, was allowed to flow through the cooler, and one to control the air flaps, which controlled the amount of air allowed to flow over the cylinders. For two years I drove a 1964 Beetle with a 1300cc engine in it, on Los Angeles freeways during the heat of the summer, and never overheated. I moved myself and my belongings 900 miles in a stock 1970 Bus and never overheated.
It is quite possible to run an air cooled engine at too low of an operating temperature, which is just as detrimental as running one too hot. Many things affect how the engine is able to maintain the correct temperature. The color of the paint used on engine components is one often overlooked; flat black is best, chrome is the worst. Chrome actually reflects heat back into your engine! Dirt and other crud on your engine or in the cooling fan will seriously degrade your cooling ability. A fan with bent or broken fins will not move air efficiently enough to do the job it was designed to do. The metal shrouding, called "tin" by enthusiasts, must be clean, straight, and have no air leaks. Last, but certainly not least, is your fuel-air mixture. If you're running too lean, you're going to overheat. Running too rich cools your engine too much and your spark plugs can foul. A properly operating and adjusted ignition system, carburetion or fuel injection system, and clean, correct air filters are necessary to keep your engine in that Goldilocks zone... not too hot, or too cold.
Horizontally opposed air cooled engines are noisy, it's a fact. Mount this engine in a small, cheap, light car, tack on 30+ years of motoring on this strange planet of ours, and you're going to get rattles, squeaks, pops, groans, and all other manner of strange sounds emanating from your machine. Air cooled engines must run larger tolerances (distance between moving parts) than liquid cooled engines because they endure a much greater operating temperature range. Metal parts grow larger with higher temperatures, and air cooled engines transfer their heat away using the metal they're made of. This, along with running a more rich fuel-air mixture for cooling, is part of the reason air cooled engines are not as clean burning as liquid cooled engines. You cannot add much in the way of smog control to an air cooled engine before operating temperatures become adversely affected.
That, my friends, is the main reason air cooled engine is no longer used in manufacture. Liquid cooled engines can be made more fuel efficient and cleaner burning. Bear in mind that thousands of air cooled engines are being assembled in small shops and garages around the world, even as you read this. It's not dead; it's finally become the people's engine.
