Liquid Cooled vs Air Cooled Motorcycle Engines

Air-Cooled Motorcycle Advantages

• An air-cooled engine is less complex than a liquid-cooled engine and may be less expensive to manufacture which in turn can contribute to a lower retail price for the motorcycle. For this reason, small-displacement air-cooled engines are popular on lower-priced motorcycles.
• An air-cooled engine requires less maintenance than a liquid-cooled engine, which can save the bike owner some time and money.
• An air-cooled engine will usually weigh less than a liquid-cooled engine, which can reduce the overall weight of the motorcycle and improve performance and fuel economy.
• Many riders simply prefer the esthetics of an air-cooled engine. The cooling fins can be a styling feature, and the engine looks less cluttered than a liquid-cooled engine.

Air-Cooled Motorcycle Disadvantages

• An air-cooled engine has to be designed to function through a broader temperature range, which can vary greatly depending on the ambient air temperature, how hard the engine is working, and how fast the motorcycle is moving. An air-cooled engine can get very hot if the rider is stuck in bumper-to-bumper traffic on a humid August afternoon – ambient air temperature is high and there’s very little air moving past the engine. For this reason, the engine needs to be designed with greater tolerances to make allowance for metal engine components to expand and contract as they heat and cool. Greater tolerances generally result in less performance compared to a liquid-cooled engine of the same displacement.
• An air-cooled engine can radiate a lot of heat into the air that’s directly around the rider’s legs, which can be uncomfortable in some conditions such as stop-and-go traffic. Harley-Davidson offers several solutions for riders who experience excessive engine heat, including the Coolflow Fan that directs engine heat downward away from the rider and Mid-Frame Air Deflectors.

Liquid-Cooled Motorcycle Advantages

• The liquid cooling system can be thermostatically controlled and designed to allow the engine to warm up more quickly from a cold start and to maintain a more-consistent temperature throughout its operation – in the harshest conditions a liquid-cooled engine will not get as hot as an air-cooled engine. Compared to an air-cooled engine, the liquid-cooled engine can be designed to offer the rider more performance while it radiates less engine heat, a benefit when riding at slow speeds in hot weather. The liquid-cooled engine may radiate less heat to the rider and passenger.
• The coolant surrounding the engine can muffle some internal noise and makes the engine sound quieter. This allows more of the desirable exhaust sound to predominate while the motorcycle still meets noise regulations.

Liquid-Cooled Motorcycle Disadvantages

• A liquid-cooled engine is more complex than an air-cooled engine. It requires the radiator and fan and a pump to circulate coolant, and tubes and hoses to route the coolant to and from the engine. This can add cost to a rider in the long run.
• The coolant and associated components add weight to the powertrain compared to an air-cooled engine. Adding weight may reduce performance slightly, but often this will be offset by the increased engine power a liquid-cooled engine can produce, compared to an air-cooled engine.
• The cooling system can fail if there’s a coolant leak or a coolant tube bursts. This would cause the engine to overheat, in which case you’d need to stop riding immediately. Engine damage could also result.
• Liquid cooling requires more maintenance than air cooling. The coolant level needs to be checked occasionally, and the coolant must be drained and replaced every two to five years, depending on the model.
• Many riders find a liquid-cooled engine less attractive than an air-cooled motorcycle engine because it may lack styled cooling fins and needs to be more densely packaged on the motorcycle. However, there are some very attractive liquid-cooled engines, and some even retain classic fins on the cylinders.

Liquid-Cooled Motorcycle Engine Options 

Liquid-cooled motorcycle engines have become more prevalent as manufacturers work to meet ever restrictive noise and exhaust emissions regulations. Liquid cooling also allows engineers to design an engine producing more power and performance.

Harley-Davidson currently employs three liquid-cooling strategies in the Milwaukee-Eight® V-Twin engines: Precision-Cooling, Twin-Cooling, and Center-Cooling. 

• The Milwaukee-Eight® V-Twin engines that power the 2025 Freewheeler® and Road Glide® 3 Trike models are Precision-Cooled, using an oil-cooled system.
• The 2025 Tri-Glide® Ultra Trike model utilizes a hybrid system known as Precision-Cooling that combines air/oil cooling and liquid cooling. Coolant is circulated only through the hottest regions of the engine – the cylinder heads – while the rest of the engine is cooled with air and oil.
• All other 2025 Grand American Touring motorcycles utilize the latest in cooling strategy, Center-Cooling where coolant is sent from the radiator to the rear cylinder head, then the front in a serial flow pattern.
• The 2025 cruisers use a similar Center-Cooling strategy where oil is sent from the oil cooler to the front cylinder head, then the rear. These systems optimize engine temperatures, especially in low-speed riding situations and hot weather, but maintain the classic styling of the Harley-Davidson V-Twin engine.

The Harley-Davidson® Revolution Max® engines that power the 2025 Sport and Adventure Touring motorcycles are all liquid-cooled and designed to produce tremendous power and torque in any condition while more easily meeting global emissions regulations.