Tuesday, September 28, 2010

Air Cooled, Oil Cooled and Liquid Cooled Engines

It was the year 2007, when Bajaj launched the Pulsar 220/200 with the oil cooler, and they advertised it as oil cooled bike. At that time I didn’t dwell much inside the all the tech, I just assumed it to be a method of cooling the engine, definitely better than the normal method, that’s why they were advertising it. And then in the year when Yamaha launched the tech-laden R15, featuring country’s first liquid cooled engine, my head went into bonkers. I kept on thinking what exactly liquid cooling is and how is it different from the pulsar’s oil cooler is after all oil is also an liquid.
So, some googling and some research on the internet helped me gather some information which I am going to share with you all.

Why Engine Cooling?


As we all know engines convert the energy produced by the burning of the fuel into mechanical energy, in our case it’s the turning of the wheels, but not all the energy generated by combustion is converted into mechanical energy, the major chunk is converted into heat energy. Now as we try to run the engine on higher revs more and more amount of heat is generated (due to the friction between the mechanical parts as well) which results in the heating of engine.
For the smoother running of the engine as well as to maintain the optimum performance the engine needs to be cooled down, and this where the cooling agent comes into the picture. There are three categories in which the engines are classified depending on the method of cooling employed:
  • Air cooled
  • Oil Cooled
  • Liquid cooled

Air Cooled engine:

As the name implies this type of engine uses air as the cooling engine. This is the most common form of engine and is available on the majority of the Indian bikes. The engine cylinder is surrounded by fins on the outside. These fins facilitate the cooling by increasing the surface area which is exposed to air for cooling. Air cooled engines are easier to manufacture and also pretty easy to maintain are pretty optimal for low capacity bikes where price is a concern as well as where high performance is not an important requirement.

This type of method is a very primitive method and the engine gets heated up pretty easily if it’s is continuously on higher rpms. The performance decreases if the engine becomes hot and running a hot engine may result engine seize as well.

Oil Cooled engine:

When Bajaj launched the pulsar’s with oil cooled engine, they forgot to add a ‘is’ between the word oil and cooled. As we know that the engine oil is circulated in the engine when it is running, and along with the engine the oil also becomes hot on running. The oil loses its viscosity on getting heated, thus if an engine is running on higher temperature, then the oil becomes thinner, thus the lubricating effect of oil reduces which increases friction between the engine parts.
To avoid this and to make sure that the oil maintains the optimal operating temperature; the oil is circulated between the radiator and the engine case, the radiator takes off the heat from the oil, thus bringing down the temperature, hence helping in maintaining the viscosity of the oil. Oil cooling is just air cooling with an additional cooling mechanism. The efficiency is definitely better than the air cooled but it’s nothing ground breaking.

Liquid Cooled engine:

This is the most popular method being used by almost all the high capacity machines as well as by our very own R15. Liquid cooling ensures stable performance in high speed riding, on up hills, in traffic jams, in all these conditions there is too much stress on the engine and engine gets heated very quickly. A liquid cooling system uses a web of passages around the cylinder to circulate coolant through.

This coolant absorbs the heat produced by the engine when running. Under high performance conditions like engine running at a higher rpm, the engine gets hot quickly; this results in the temperature of the coolant to rise.
The coolant is then sent to a radiator which dissipates the heat by running air flow or an electric fan. The coolant is then circulated back to the engine. This constant circulation of the coolant constantly cools the engine. Thus engine runs cooler, can maintain high speeds for a long time as well as the performance is not hampered. The liquid engine also has a longer life as compared to an air cooled engine. The efficiency of liquid cooled engine is any day better than its air cooled counterpart.

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