The Pros and Cons of Liquid-Cooled and Air-Cooled Motorcycle Engines – Jalopnik

Cooling fins are an iconic feature of motorcycle design. These blades made an early impression, with their parallel lines encircling the cylinders of classic bicycles from day one. Whether it’s the striking V-shaped engines of American cruisers, the upright twins of vintage British motorcycles, the outstretched arms of a BMW boxer or the transverse wings of a flying Moto-Guzzi, cooling fins have seared themselves into our collective consciousness. You can dress up your bike with fancy decals, but nothing says “motorcycle” more than a cool set of fins.

Liquid-cooled motorcycles are sometimes lazily referred to as “water-cooled” and have a radiator, usually located at the front of the frame. An air-cooled motorcycle doesn’t have that, and doesn’t need any of the pumps and pipes of a liquid-cooled motorcycle. But its rough-hewn simplicity is increasingly being surpassed by the reliability, economy and power of liquid-cooled alternatives. Japan’s Big Four – Honda, Kawasaki, Suzuki and Yamaha – led the charge, especially in the 1980s, when they discovered they could more easily keep engine temperatures stable with thermostat-controlled liquid cooling.

Coolant is pumped around the cylinder jackets, cooled in the radiator and recirculated. So those cooling fins are no longer necessary – although some manufacturers simulate their distinctive look by adding decorative stripes to their modern, liquid-cooled engine blocks and heads. Yes, we’re looking at you, Triumph Bonneville. Styling considerations aside, what are the pros and cons of liquid cooling versus air cooling? And does it come down to a choice between being cool or looking cool?

Well-controlled engine temperatures mean predictable fuel-air ratios, better fuel efficiency and lower emissions. Additionally, having cooling jackets around the combustion chambers also helps suppress noise. Whether owning a quiet, smooth-running motorcycle is an advantage or a disadvantage depends on your point of view, but less engine chatter means the exhaust note is more prominent, and it can be tuned to a satisfactory level without annoying every neighbor within 10 miles.

Air cooling purists argue that liquid cooling adds even more things that can go wrong, with pumps, hoses, coolant and radiators requiring constant attention and occasional replacement, with the added risk of leaks and corrosion. Yes, liquid cooling requires more maintenance than air cooling, but engine design has come a long way since your grandpa’s ride in the 1970s. Today’s liquid-cooled bikes can go thousands more miles between valve inspections than air-cooled bikes, albeit with frequent cooling system checks. So it depends on which type of maintenance you prefer: replace the coolant and check the hoses every few years, or adjust the valve mechanism and change the oil much more often.

Further complications arise with the longitudinal air-cooled V-twins of Harley-Davidson and Ducati motorcycles. Here the front cylinder gets more airflow than the one behind it, which limits how far the engine performance can be pushed before the rear cylinder turns into a barbeque grill on your bum. Moto-Guzzi gets around this by mounting its V-twin across the frame, with the cooling fins spread wide into the wind.

BMW goes even further and achieves an even airflow by laying the horizontally opposed, air-cooled boxer engine flat. This evergreen design was voted by our readers as one of the best engines of all time – not just motorcycle engines. The air-cooled boxer is still going strong today in models like the vintage-inspired BMW R 12 G/S, albeit with an oil-cooling advantage in store. Hybrid air/oil cooled designs can dissipate more heat than air cooling alone, although they do not qualify for dedicated liquid cooling because oil has less heat capacity than coolant.

In 2012, an air-cooled Monster 1100S with a displacement of 1,078 cc delivered 95 hp at the crankshaft. Not bad, huh? Well, not so fast. Its liquid-cooled successor, the 1,198 cc Monster 1200 R from 2015, delivered 150 hp – and the 2026 model year has a similar story to tell. The current air-cooled 803 cc Monster 797 produces 73 hp at the chain, while its liquid-cooled 890 cc stablemate produces 111 hp. That is a power gain of more than 50% with a slightly more than 10% larger engine capacity. It’s not a competition; liquid-cooled Ducati Monster engines rev higher and produce more horsepower and more torque than their air-cooled counterparts.

That’s not to say you can’t get huge torque from an air-cooled engine. Of course you can, as any die-hard Harley-Davidson diehard will truthfully confirm. It’s not just American V-twins either. The 1,802 cc BMW R 18 boxer engine has torque for days. If you’re not looking for high-revving power, an air-cooled motorcycle may be all you need.

But the most current air-cooled creations are aimed at the retro market. Yamaha didn’t have to try too hard with its TW200, as this lightweight has been in production virtually unchanged since 1987, while Honda with its XR650L sits right between this Tdub and the hard-fought Beemers and Guzzis. Honda also recently released a GB350 Special Edition, seemingly in an attempt to make something even more vintage than vintage.

Royal Enfield has surprisingly switched to liquid cooling for its 450cc Himalayan model, but everything else from this classic manufacturer is still air-cooled, including its beautiful 650cc Continental GT. Indian and Harley-Davidson have a range of both air- and liquid-cooled motorcycles, with the latter even making a bet with its “Twin-Cooled” Milwaukee-Eight engines in some touring models. While trying to hide the radiators in the fairings, these dual-cooled power plants use liquid cooling for the cylinder heads, while keeping the block air-cooled and finned.