9th September 2019

Air-cooled engines: pros and cons

Air-cooled engines: automotive marmite. Those that love them do so with unbridled passion, but those who don’t view them with trepidation and in perplexity. We think it’s fear of the unknown that puts people off as there’s a lot to love about air-cooling.

In automotive terms, Volkswagen was the best-known pioneer of the technique, most famously utilising flat-four air-cooled engines in the Beetle and Type variants since the 1930s. Porsche, of course, the Czech company Tatra, Trabant, Fiat and Citroën have all adopted air-cooling for a wide range of vehicles, and even Honda and Chevrolet, among others, dabbled with the concept.

Most common for motorbike, aviation and small commercial engine use, the basic premise of the air-cooled engine is that it offers reduced maintenance, weight and complexity, both in terms of design and installation. As the name suggest, the engines rely on a constant flow of air to cool, rather than the circulation of water or coolant. This design is ideal for the aforementioned applications as they spend a large proportion of time moving at relative speed and are not, generally, enclosed when in situ. Cars, on the other hand, are not so simple. Heavy traffic, closed engine bays and restricted air flow all jeopardise optimal operating conditions; when an engine is too hot, performance can be compromised and damage incurred.

Of course, water-cooling is not without its pitfalls. The systems are far more complex and reliable operation relies upon all components being in good health; the water pump, thermostat and radiators, for example, are all subject to wear and part failure can lead to catastrophic engine damage. This is at odds with what was arguably the main driver of automotive air-cooled adoption: reduced maintenance. Quite simply, air-cooled engines are designed to run at high speeds for long periods.

A distinctive characteristic of air-cooled engines is the noise. Due to the lack of water ways throughout the block and head to aid sound insulation, the engines can often sound louder than their water-cooled brethren. However, that is only one contributing factor: to increase airflow and help keep operating temperatures in check, air-cooled engines are usually manufactured in ‘flat’ arrangement. This also helps lower the centre of gravity, offering improved handling and packaging benefits, too. Assuming a four-cylinder engine, this means that the pistons are not in-line or in a vee, as per traditional configuration, but opposing the crankshaft with two horizontal banks of two pistons. This lends itself to a very distinct sound that, you guessed it, you’ll either love or hate.

Larger capacities were also manufactured in large numbers. The 911 has made the air-cooled flat-six a truly iconic engine, and Tatra even produced an air-cooled 8-cylinder. The downside is that the larger the capacity the more difficult efficient air-cooling becomes: generally, bigger engines produce more heat, hence the fastest 911s normally relying on high levels of tune with more revs and greater specific capacity, rather than significantly increased displacement.  

Are you an air-cooled diehard or water-cooled worrywart? In the comments below we’d love to hear tales of why you love or loathe air-cooling. Let us know the details of the adventures this now defunct technology has taken you on.