Air or Water Cooling – Which is Best?

Entire generations of riders have sworn by air-cooled engines and Harley took a whole ration of wrath when they decided to introduce liquid cooling into the Twin Cam 103 a few years ago.  Mother Davidson was far from the first – in reality – they were one of the last – but is there an advantage to cooling systems?

The short answer is yes – but whether you see it as an advantage or a disadvantage depends on a lot of things.  Buyers preference, maintenance programs, induction systems, and a variety of outside influences all contribute to whether air or liquid cooling is best.

Liquid – water or antifreeze – cooling has been used in internal combustion engines for over a century and first started making inroads into motorcycles with the large-scale importation of bikes from Japan in the 1970s.  Kawasaki, Honda, and Yamaha built hundreds of thousands – if not millions – of bikes in that decade and in many ways, the presence of a radiator in a bike was the defining feature between Japanese and American bikes at the time.  It’s worth noting that, at least anecdotally, the rumor persists that after the AMF management buyout in the early 1980s, the EVO motor was originally envisioned as a liquid-cooled motor – to compete with the influence that the Japanese builders were having on motorcycle design among North American riders at the time.  Ultimately, of course, the EVO was a traditional air-cooled engine (and probably the single reason that H-D survived the AMF quality control years).

So why would one company choose air cooling or water?  Here are some of the primary facts that the various powerplants bring to the table:

  • Engines that operate at higher RPM really need water cooling, as the frictional coefficient and coolant passages reduce hot spots internally.
  • The water jackets for a liquid-cooled engine allow the engine to run quieter.
  • Introducing cooling means a more complicated assembly as well as more systems to fail – be it the radiator, the oil cooler, or more machining steps for engine block preparation.
  • As a result of fewer systems, air-cooled platforms are “usually” less expensive.
  • Air cooling tends to make fuel injected systems harder to tune due to a wider variance in temperatures based on ambient external temperatures, airflow over the block, and even oil viscosity.
  • Rising emission standards make air cooling more difficult to execute, due to the wider range of operating temperatures and the inability to control temperature.
  • Liquid-cooled engines generally have tighter tolerances as a result of the various sealing surfaces needed internally, leading to, at least potentially, faster and higher revving motors.
  • Air cooled engines are – obviously – hotter. (A fact that any Harley rider can attest to if stuck in traffic on a hot summer day.)  At the same time, air-cooled engines demand a certain amount of airflow over the crankcase to ensure cooling.

Are any of these critical to a buyer’s decision in the dealership?  Unlikely.  Brand loyalty has almost always been a bigger factor in determining where your next bike is coming from, but as emissions regulations force more manufacturers into liquid cooling in the developed world, the air-cooled engine is becoming more and more of an anomaly.  At the same time, these systems can be more complex and that could mean less time “fixing” in the driveway and more time being repaired at the dealership.

No matter what, though, being on the bike is better than sitting in the office!

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