Air- vs. Liquid-Cooling For Your Motorcycle

Both means of engine cooling have their pluses and minuses

2019 Harley-Davidson Forty-Eight

Jeff Allen

The liquid-cooling of engines has been a trend for more than a hundred years but, unlike advancements in other areas (suspension, fueling, and lighting, for example, where the technological boneyard starts at the last model year), air-cooled engines have shown a remarkable longevity. Nowhere is this dichotomy more prevalent than in American V-twins. That's in part because there are benefits to air-cooling. Foremost, simplicity. Air-cooled engines require fewer parts, both for manufacturers to build and for consumers to fix. Unique to motorcycles, another advantage can be aesthetic. Because motorcycle engines often sit in plain sight, the look of cylinders bristling with delicate cooling fins is, understandably, too cool for some to resist.

2019 Indian Scout

Jeff Allen

The benefits of carrying heat away from the combustion chamber with liquid, though, are significant. Liquid-cooling pulls heat away from the engine much more efficiently, and that allows manufacturers to increase compression ratios and extract more power without overstressing internal parts. There is also increased efficiency from tighter tolerances and leaner fuel-to-air mixtures. And then there’s noise—we often think of the exhaust pipe being where the noise comes out, but the mechanical din that emanates from an internal combustion engine is significant. Having the cylinder jacketed by water for cooling has the fringe benefit of cutting down on clatter, meaning companies can spend the noise savings on the sweet song of the pipe that we all enjoy.

There’s no real question that liquid-cooling is the future. Luckily, metallurgy and technology have also allowed air-cooled mills to remain relevant. Long live both, we say.