How an Air-cooled Engine Works

The premise of an air-cooled engine is actually pretty simple: Let air flow over the engine to keep it cool.But since this article needs to be a little bit longer than that, we'll touch on a few more details (for my editor's sake, anyway).

Most modern cars use water-cooled engines with radiators, water pumps and hoses that circulate a water and coolant mixture throughout the engine. The heat from the engine is transferred to the coolant, and then the coolant is cooled in the radiator and sent back around again.

Air-cooled engines want none of this. They rely on good old-fashioned air to cool them down. To be fair, all engines are technically air-cooled because even water-cooled engines use air to cool the fluid in the radiator. But let's not split hairs.

Air-cooled engines have fins extending out from the engine to pull heat away. Cool air is then forced over the fins -- typically by a fan in cars. For aircraft and motorcycles, the vehicle's speed alone moves enough cool air over the fins to keep the engine cool.

Some air-cooled engines may also have ducts around the engine to keep air flowing to the hottest areas. Some aircraft engines may even have baffling systems that channel high-pressure air into the cooling fins.

Another design feature that keeps an air-cooled engine's temperature low is horizontally opposed cylinders -- they face away from each other and are spread farther apart than a typical water-cooled engine. This allows air to flow freely over the fins. Some air-cooled engines also make use of oil coolers to keep the oil temperature low.

This doesn't sound much like magic anymore does it?

The air-cooled engine has had a long and well-loved history. At least, depending on whom you talk to. In the 1960s and 1970s some carmakers used air-cooled engines to power their vehicles. The 1964 Porsche 911 may be one of the fastest air-cooled engines, but the Volkswagen air-cooled engine may be one of the most beloved. It was used in the original Beetle.

You'd be hard-pressed to find an air-cooled engine rolling of the auto assembly line these days, but that doesn't necessarily mean they're anywhere near dead.

If you hop on a motorcycle, all-terrain vehicle, or even a common riding mower then you're probably experiencing an air-cooled engine (although some motorcycles are liquid-cooled). But it's aircraft that have had the longest running air-cooled track record because many helicopters and small planes have remained air-cooled right from the beginning.

So an air-cooled engine has no need for a radiator, a water pump, coolant, hoses or any other associated parts a liquid-cooled engine has. But is this actually a good thing?

The short answer: Sometimes.

Obviously, and air-cooled engine doesn't have coolant leakage problems and won't ever require things like the water pump or radiator to be replaced, which can be a great thing. Typically, they're lighter than liquid-cooled engines, too, because they have fewer parts.

Air-cooled engines also warm up a lot faster than liquid-cooled engines and don't have any risk of the coolant freezing, which is beneficial if you're operating the vehicle in extremely cold temperatures.

But there are some considerable drawbacks, too. For starters, air-cooled engines are more likely to overheat. Yeah, that's a bummer. They can also be more expensive to build and the large fans used to cool the engine can take away a lot of power.

This doesn't mean that air-cooled engines are bad or ineffective. In fact, for motorcycles, recreational vehicles and certain aircraft the air-cooled engine works extremely well. But on cars, the common consensus is that the drawbacks outweigh the benefits.