Air Cooled vs Oil Cooled vs Liquid Cooled Engines: Which one is the best?
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Every time you crank up the internal combustion engine of your two-wheeler, there are countless explosions taking place inside the cylinder, which, along with the frictional forces of the various moving parts inside, generate a tremendous amount of heat. Unless there is a cooling force which keeps the temperature in check and allows the internals of the engine to perform at an optimum level as overheating can cause the motor to stall and self-destruct. Depending on the application it has been designed for, a two-wheeler’s engine can adopt from three different types of cooling methods. These are one of the features that are very important in commuter bikes. Let’s take a look at how it all works.

Air cooled

This is the most basic method among the three where the natural air is used as a cooling agent. The working principle is pretty straightforward, where the outer casing which houses the engine cylinder is surrounded by fins that create channels for passing air to take away the heat dissipated by the happenings inside. The fins also increase the surface area, of the casing, allowing the heat to dissipate quickly. Air cooling is a cost-effective method but it isn’t the most efficient choice for high-performance engines which rev high and can generate a lot of heat.

If engineered well, it’s quite a reliable method for cooling though, as there are lesser things to go wrong which would otherwise affect the working of an engine. This method is usually adopted for small capacity engines which generate a modest amount of power and resultant heat. Air cooling is also used for large capacity engines which do not rev too high. However, large capacity air-cooled engines work best in colder climes as the heat generated near the rider’s legs makes the motorcycle troublesome to ride during hot and stop-go conditions. Furthermore, air-cooled engines run richer, are less efficient, more polluting and noisier than their liquid cooled counterparts due to the lack of sound insulation which a cooling apparatus provides. This feature can be one of the features that are very important in commuter bikes.

Air / oil cooled

This is the intermediate option which is deployed to keep engine temperature in check. In addition to adoption of air cooling as discussed above, this method also makes use of an oil cooler which cools down the temperature of the engine oil. The engine oil which is circulated within the engine when its running absorbs the heat generated inside and beyond a defined temperature level begins to lose its viscosity. As the density of the lubricant decreases, friction between the internal components spikes and as a result, engine temperature too begins to shoot north.

To avoid this, and to make sure that the engine oil maintains an optimal operating temperature, it is circulated between ‘oil cooler’. This mechanism too makes use of atmospheric air to cool down the engine oil which passes through a radiator-like, externally mounted oil cooler. As there is already an oil circulation system available for lubrication, this oil is also piped to the cylinder head and used as a liquid coolant. Compared to an oil system used solely for lubrication, oil cooling requires additional oil capacity and a greater flow rate through the oil pump.

Oil cooling is an ideal method for engines where air-cooling is sufficient for much of the running time, but an additional amount of cooling is required for a specific performance range, where it is vital that the engine oil retains its viscosity and minimizes friction. However, since atmospheric passing air is still the basic element used, where cooling improves only when speed rises, oil cooling is not as efficient as liquid cooling and cannot be installed on high-performance engines that produce huge amounts of heat during all operating conditions.

Liquid cooled

This is the type of cooling method used in large capacity motors since they rev high, generate higher amounts of power and require ideal cooling during all operating conditions. The concept of liquid cooling for a motorcycle engine is similar to cars, where a coolant is circulated through internal channels around the motor. Because the coolant absorbs the heat from the engine, its own temperature must be brought down. As a result, it is pumped towards a radiator which cools it down using atmospheric air and additional fans which activate when the vehicle is moving at slow speeds.

The cooled down fluid is then circulated back around the engine, where a constant cycle of this process keeps the engine temperature under control. This method allows the engine to perform reliably and at an ideal operating temperature during all conditions, especially when it has to operate in stressful conditions for longer durations. Because the cooling components create additional insulation around the motor, liquid cooled engines are quieter, more efficient and environment-friendly in comparison to their air-cooled counterparts. This feature can help you get the features that are very important in commuter bikes.

Whichever cooling system the engine of your two-wheeler employs, make sure you don’t run an air-cooled engine near its redline for really long durations, top up oil levels regularly if the motor is oil-cooled, and keep a check on the coolant and its delivery systems if your bike has been fitted with a liquid cooling setup.

 

 


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