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2007 Harley-Davidson Sportster XL-883

Air Cooled vs. Liquid Cooled Motorcycle Engines

  • Air cooled motorcycles run quieter.
  • You’ll tend to see them more on cruisers as most cruisers typically run at lower RPMs then sportbikes, which tend to be liquid cooled.
  • Air cool provides more simplicity, representing one less thing which could break or need to be replaced.
  • Liquid cooling rads are sometimes fragile, and external or aftermarket oil-coolers can also be expensive and likely to break in a drop. Air cooled bikes may be cheaper.

  • Air cooled is also likely more feasible for single cylinders (big thumpers) or parallel twin engines rather than V-Twins, where the back cylinder would remain hot.
  • In liquid cooled engines, the circulating liquid evens-out hot spots in the cylinder head. This is better for detonation control and for emissions. The combustion chamber surfaces can be kept hot enough to encourage more complete combustion, but not so hot so as to promote detonation or high NOx emissions.
  • Liquid cooling is better for long-term durability since it allows tighter build tolerances.
  • Liquid cooled engines transfer the heat to the rad at the front of the bike, making a long ride or a traffic grid lock more tolerable for the rider.

What you’ll want depends entirely on your ride. Sportbike or other high-revving engine, you may want to make sure you’re getting something with liquid cooling. Scooter or cruiser can probably get away with air-cooling. Many people say Harley-Davidson Sportsters never overheat, but if they do get hot, there are always things you can do, such as switching to a full synthetic motorcycle oil, or adding an OEM or aftermarket oil cooler.

Check out Adri’s air-cooled 2007 Harley-Davidson Sportster!
2007 Harley-Davidson Sportster XL-883

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5 comments

  1. water cooling on a bike is nonsense. Aircooled bikes don’t overheat

  2. Hello,

    Air cooled engines need much richer carburetion to cool them this means they pollute much more than liquid cooled engines. Liquid cooled engines can operate with carburetion set to burn all the fuel in the mixture. This chemical balance is called stoichiometric combustion where all the fuel is burned. Air cooled engines will never run with stoichiometric combustion because they would quickly overheat.

    Water jackets in an engine act as sound insulators therefore liquid cooled engines are quieter than air cooled engines.

    Its inevitable that governments will regulate motorcycle tailpipe emissions which will be the end of air cooled motorcycles.

    Rgds
    Eric

    • I am with Eric on this. Harley and those who have followed its lead have perfected the air cooled V-twin engine to the extent it can be. They are relatively clean and powerful, but a water cooled bike which allows tighter tolerances will pollute less and rev higher, producing more horsepower. The proof is riding on the road now. Look at the amazing power difference between Harley’s lower displacement, water cooled V-Rod and their larger displacement cruisers.

      I am riding my second Harley touring model and I love it, but I think by the time I get around to getting my next one it will be water cooled and it likely won’t have push rods.

      Jefe Smith

  3. musictoone@yahoo.com

    I can’t go back to air cooled. loved my yamahas but liquid cooling has been awesome in the las vegas desert. my vtx has a fan that comes on just like a car to keep cooling even if at a stop light. a few more parts? yes, but way worth it. if I didn’t live in the desert? then air would be fine I think.

What do you think?