The engine, the power house and the heart of the motorcycle. Engines convert Chemical energy basically fuel like petrol, diesel etc into heat energy by combustion within the engine and that is converted to mechanical energy which is transmitted via the crank and transmission to the wheels. The by-products of the internal combustion include the energy produced which pushes down the piston, the exhaust gases and a lot of heat. As we continue to accelerate and run the bike on higher revs, more heat is generated. The heat generated from the engine needs to be kept at an optimum level to get best performance from it. Hence it is essential to maintain the engine around this temperature by different cooling methods for best performance.

Cooling is primarily is done by two major methods:

1. Air cooling

2. Water (Liquid) cooling

Air cooled engines

Air cooling can be classified into two variants:

A. Naturally air cooled

As the name suggests, air is the cooling medium. Air that is blowing past the engine during transit is made use of to cool the engine. The cylinder is designed with fins to help in this process. Fins are a set of parallel slats to admit air. Basically these fins provide a larger surface area and also increase air turbulence around the engine to increase heat dissipation. Eg., Bajaj Pulsar 150, Hero Honda Karizma ZMA, Honda Unicorn etc.

B. Forced air cooling

This method of cooling is primarily used in vehicles where the engines have very little access to natural air flowing across the cooling fins. Fans are used to force air go past the cylinder block. This is the most economical way for cooling and is usually used in low displacement scooters like Honda Activa, Suzuki access, Bajaj Chetak, Lambretta etc..

Water (Liquid) cooled engines 

The engine performs better when its temperature remains optimum & constant. Water(liquid) cooling is a method which is used to keep the engine temperature constant. This a popular method used for cooling in high rpm engines & many large engine capacity bikes where performance is vital. The engine has a coolant jacket, where water mixed with anti rust & anti freeze compounds circulates and absorbs the heat generated. This mixture is passed to the radiator where the heat is exchanged & cooled down by on coming air. Brush less fans are added to the system to cool the water quickly when the temperature raises beyond optimum levels.

Now one would think that it would take forever to reach the optimal operational temperature due to the constant cooling right? To overcome this situation a thermostat is used to restrict the circulation of water until the optimum temperature is reached, this helps the engine gain optimum temperature quickly. This is done by the thermostat choking the circulation of water till the pre-designed temperature. An additional reservoir is connected to the radiator to store the vapour mixture which is released from the radiator cap when the temperature rises. Similarly the same is pulled back into the system when the water level drops in the radiator.

The other untold advantage is the management of the NVH (Noise,Vibration, Harshness), which is lowered due to the dampening of it by water. Though this system is complicated to build, its high efficiency makes it most desirable.

Example of motorcycles that use this system are Honda CBR 250R, Yamaha R1, Kawasaki Ninja’s, Suzuki Hayabusa etc

So then what are Oil cooled engines?

This technique, although not a standard method is basically used to cool the engine oil. The engine oil lubricates all the moving parts of the engine and hence minimizes friction. The oil film at higher temperatures tend to break due to cracking of molecules. This in turn increases the wear of the engine. Thus it becomes essential to cool the engine oil. This helps in keeping the engine oil at optimum temperature. As a solution to this the oil is pumped across to the cooling radiator, where the oncoming air cools the oil and is then sent back to the engine. Eg., Pulsar 220, Pulsar 200.


  1. I have Pulsar 150 DTS-i purchased in Nov 2011. The bike’s engine is getting hot these days because of unknown reasons and also the milage is getting dropped considerably. I have recently (approx 15 days ago) put Motul 20w50 Fully Cynthetic Engine Oil.

    Do you have any clue on this?

    Amar Narkhede

  2. What are the tips to keep the radiator clean .is it ohk to put a index PC size pan on to it like I saw in YouTube.will it work cool the engine

  3. How do i know the optimal engine temperature in the case of a liquid cooled engine? and how do i when the thermostat stops choking. How many bars in the console of the KTM Duke 200 would indicate the optimal temperature, and the bar indication at which the thermostats stop choking? Also what damage can be done to the radiator due to mud particles/debris and jet washing?

    • Optimal engine temperature in the case of liquid cooled engine is maintained by itself and the liquid cooling ensures that the engine is working in optimal range for best performance and efficiency. The number of bars indicated after a good engine warm up of 50kms or so would be the optimal temperature and the same can be obtained from your display.

      Thermostat stops choking when your engine idles at a steady desired rpm. Usually at the first start of the day, the FI system in KTM Duke 200 idles at more than 1500rpm for the first couple of minutes which explains that the thermostat is choking. The rpm slowly settles down to 1500rpm and finally the choking is stopped.

      TIP: We always recommend to idle for 2 minutes when you start in cold conditions. This ensures circulation of engine oil to all the corners of engine.

      Mud Particles/Debris causes obstruction for the working of radiator thereby making it less efficient to cool your engine. Jet washing with high pressure, causes the fins to bend which reduces its surface area hence allowing lesser atmosphere air into the radiator for cooling.


    • Hi Sharath,

      It is not possible to adapt liquid cooling to the oil cooled engine. Liquid cooling requires a dedicated system that has to be made along with the engine design and cannot be added to an existing air cooled engine :)

    • Hi Harsha,

      Well it is definitely possible but is a pain staking process and it will not be anywhere as functional as the original setup. There are a lot of parts that needs to be replaced and added, we would recommend you to stick to the stock setup.


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