Motorcycles - Air Cooled vs Liquid Cooled
| Air cooled | Liquid cooled |
|---|---|
| An air-cooled engine uses nothing more than the outside air to cool off the internals. | A liquid-cooled engine of course requires the liquid or coolant along with a water pump, the radiator and other components that disperse the coolant to remove excess heat from the engine. Anti-freeze and rust inhibitors. That means more stuff to maintain and parts that can potentially break. |
| You can easily tell an air-cooled motorcycle by the “fins” built into the engine block that act as heat dissipaters. | A liquid cooled bike features an internal cooling system much like an automobile and requires coolant. |
| The air-cooled engine needs a constant flow of air to cool off the engine, something hard to come by when stopped at signal lights and crawling along in traffic. | Liquid-cooled engines on the other hand work more efficiently and cool off the engine better than air-cooled especially in hot weather and stop-and-go traffic. |
| Cheaper | More expensive |
| utilize an air-cooled system very well when in constant motion and generating air flow while the engine revs at low RPMs. | better heat tolerance, easily handle higher RPMs and excel in excess traffic and hot weather. Less air pollution because of the overall efficiency and better fuel to air ratio - and less noise pollution because of the internal water jackets that help muffle the sound of the engine. |
| Air-cooled motorcycles proceed at the mercy of outside temperatures and capacity to create free airflow which often creates hot spots around the engine and inconsistent cooling. | Liquid cooled bikes operate like the human body by constantly regulating the internal temperature and ability to self-cool. Therefore, these bikes function in a much tighter temperature controlled environment and quickly breakdown when out of that space for an extended period of time. |
You can often identify an air-cooled engine by the fins on the engine block and/or cylinder head(s) that dissipate heat, and are sometimes used to striking visual effect, too. Airflow over the fins will help carry heat away more quickly. That said, if an air-cooled motorcycle remains stationary for a particularly long time, especially in hot weather, it’s a good idea to shut the engine off to prevent overheating.
Air-cooled engines rely heavily on a proper tune to remain cool — especially the proper air-fuel ratio on a carbureted engine, which can sometime be set to an overly lean condition by the manufacturer to satisfy emissions requirements. It’s also important to have fresh oil.
Oil gradually loses its ability to lubricate after repeated heat cycles, so do be diligent about sticking to your manufacturer’s recommended oil change schedule. Similarly, many air-cooled bikes have a larger oil capacity than water cooled bikes to promote lower oil temperatures.
In general, air-cooled bikes are simpler, with significantly fewer parts to maintain. The drawbacks to air cooling are inconsistent operating temperature, greater noise levels, and increased possibility of overheating in stop and go conditions.
Like most internal-combustion-powered automobiles, liquid-cooled bikes have a radiator mounted in an area of high airflow: coolant circulates both inside the engine and back out through the radiator via water pump.
Liquid-cooled engines do serve more purposes than just engine cooling. Under pressure from the EPA to reduce exhaust emissions in the 1980s, motorcycle manufacturers found that it was easiest to keep air-fuel ratios consistent when engine temperature was steady, which could easily be regulated by the thermostat in a liquid-cooled system.
Coolant does need to be changed every so often, typically at two to five-year intervals. Rubber hoses are also consumable items, and the possibility exists that hard components like water pumps and radiators can develop leaks and other issues. On the surface, it seems like liquid-cooled engines have greater maintenance requirements, but that’s not entirely true. Cooling systems may be more complex, but because the engine maintains a stable temperature, the service intervals for other engine components like checking valves are less frequent.
Liquid-cooled engines are also quieter than their air-cooled counterparts. Water passages surround the combustion chamber and serve to dampen the mechanical noise.