Air Cooling vs Liquid Cooling – What is the Difference? Story bumped up!

I was never as big a motorcycle enthusiast as I am now. If I go back a few years in my life then my whole interest/opinion about motorcycles was way different than what it is currently. Like the general junta, at that time I was more concerned about which new bike is being launched, what is the engine capacity and what is the power rating – basically the glamorous superficials! I was least interested to know how this power is generated or what technologies go in making the motorcycle work.

Back then it was mostly about small engines, majorly led by Hero’s 100 ccs (Hero Honda then) which came equipped with conventional air cooling. But when Bajaj introduced its bigger Pulsars with ‘oil cooling’, followed by R15’s ‘liquid cooling’ we started getting global technology in India.

It is very interesting to learn how engine cooling works and we will discuss the various ways manufacturers use to achieve this, in simple terms.

Why Engine Cooling?

As we all know engines convert energy produced by the burning of the fuel into mechanical energy; in our case it is into turning of the wheels. But not all the energy generated by combustion is converted into mechanical energy, the big chunk gets dissipated as heat energy. As we try to run the engine on higher revs, higher amount of heat is generated (due to friction between mechanical parts) which results in heating of the engine.

For a smooth running of the engine as well as to maintain an optimum performance, the engine needs to be cooled down, and this where the ‘cooling tech’ comes into the picture. There are three categories we can classify engines based on the cooling method employed…

  • Air cooled
  • Oil Cooled
  • Liquid cooled

Air Cooling vs Liquid Cooling – Pros & Cons

Air Cooled engine:

As the name implies this type of engine uses air as the cooling agent. This is the most common form of engine cooling and is available on majority of Indian bikes. The engine cylinder is surrounded by fins on the outside as you can see in the picture below. These fins facilitate cooling by increasing the surface area which is exposed to air for cooling.

Pros: Air cooled engines are easier to manufacture, are cheaper and pretty easy to maintain. They are generally used for low capacity bikes where price is a concern and when high performance is not an important requirement.

Cons: Least efficient of all and hence can not be used in high performance engines

Air Cooling vs Liquid Cooling

This type of method is very primitive and the engine gets heated up pretty quickly if it is continuously run on higher rpms. The performance of the motorcycle decreases if the engine becomes hot and running a very hot engine may even result in engine seizure as well.

Motorcycles Using Air Cooling – Almost all commuter motorcycles like Splendor, Shine, Pulsar 150 etc

Oil Cooled engine:

This type of tech was marketed and made popular in India by Bajaj when they introduced it on their bigger Pulsars. We already know that engine oil is circulated within the engine when it is running, and along with the engine the oil also becomes hot on running and starts loosing its viscosity (in simple terms – thickness). This has a direct impact on its lubrication capability.

Thus, if an engine is running on higher temperature the oil becomes thinner and with the reduction in lubrication, friction between engine parts increases.

Air Cooling vs Liquid Cooling

To avoid this, and to make sure that oil maintains an optimal operating temperature; the oil is circulated between an ‘oil cooler’ (pictured above). This oil cooler is cooled by the flowing air and it cools down the engine oil. This cooler engine oil is again sent back to the engine via the other jacket.

This process brings down the operating temperature of oil and helps in maintaining its viscosity. In essence, oil cooling is just air cooling with an additional cooling mechanism.

Pros – This is more efficient than simple air cooling. It is cheaper as well as technologically simple and easier to maintain.

Cons – Not as efficient as Liquid cooling and can not be installed on high performance engines.

Motorcycles using Oil Cooling – Pulsar 220, Apache 200, Karizma ZMR.

Liquid Cooled engine:

This is the most popular method being used by almost all the high capacity machines in India and abroad. The concept of ‘Liquid cooling’ in motorcycles is very similar to what it is in cars. It ensures stable performance at high speed riding, on up hills, in traffic jams etc. 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. This cooler coolant is then circulated back around the engine. This constant circulation of the coolant keeps the engine temperature under control.

Air Cooling vs Liquid Cooling pic
Liquid Cooled Dominar 400’s Radiator

Pros: Liquid cooled engines run cooler, can maintain high speeds for a long time and the performance is also not hampered. They also have a longer life as compared to an air cooled engine. The efficiency of liquid cooled engine is way better than its air cooled counterpart.

Cons: They are costlier and complex to make. Relatively costlier to maintain as well.

Motorcycles Using Liquid Cooling – Yamaha R15, Bajaj Dominar 400, KTM Duke 390 etc

Air Cooling vs Liquid Cooling – There are obviously other facets and deeper details on this subject but this article is intended to provide the basic understanding in as simple a language as possible. Probably, a more comprehensive story will follow sometime later…

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  1. Good informative article but you forgot one major advantage of liquid cooling over air cooling , it doesnt allow hot spots to be formed , i.e., no part of engine is hotter than the other .

    But for street bikes i think air cooled engines are better .

  2. “The liquid engine also has a longer life as compared to an air cooled engine”

    i disagree. engine life is not only determined by the method of cooling. and it also depends which category of engine (bike or something else). depends also on how you operate the bike. i’m sure we all have seen age old splendors and cd-100s on the indian streets

  3. Thanks man , i was too thinking the same oil is liquid too, what might be the difference.
    your article is just the quick info i need to know, thank you very much

  4. @pankaj because the harleys and the bullets are slow revving cruisers so the engine doesnt heat up much…but that too depends on the way you ride them..if u rev a bullet really high for a while, it will overheat.. if u relax and ride a bullet, you can ride it all day with no probs..

  5. hi i want to do some modification on my pulsar 180 , 2013 new modal
    …. sonsimply i want to fit oil or liquied cooled set
    so plz help to solve my prb and i want to knw abt dis prd price also

  6. Although nicely expressed Deepak, I am afraid this explanation is not quite complete.

    In the bike you refer to, you are absolutely right about the lack of the word “is”; but oil cooling can be used for more than maintaining the viscosity of the oil. For example Suzuki used it to directly cool critical areas of their air-cooled SACS engines. In part SACS uses spray cooling of the piston crown, but is not limited to that. This sort of cooling has many advantages, some even over water cooling, but obviously does require a larger oil pump and oil cooling radiator. If you run an engine with a turbo-charger, oil cooling is all the cooling that the bearings can get.

    Perhaps the biggest difference between liquid cooling (including oil cooling) and air cooling is the ability to avoid over-cooling the engine when under low load. For this a thermostat is included in the system, with a radiator by-pass. This allows the cooling system to be sized for worst case situations, including high ambient temperatures, without affecting the best case situations too badly. Note that the ambient environment affects all engines, even low-stressed cruiser types. Virtually no motorcycle air cooling systems do this sort of management. Some fan-driven car cooling systems do it.

    That a thermostat and by-pass allows near constant, and modestly near to optimal temperature in both the engine itself and the lubricant is why liquid-cooled engines wear better, and so last longer. An important part of this is the allowance of much closer tolerances between the moving parts, and maintaining those close tolerances. This also makes it much easier to meet modern emissions standards to avoid pollution. The liquid also tends to absorb the vibration energy of combustion, and so those engines can be quieter.

    Another issue is the speed of warm-up. Much of an engine’s wear occurs when running cold, with cold oil in it. This is where that ability to by-pass the radiator makes a big difference. It is also a scenario where air cooling works against the fins being sized for worst case situations. In my relatively limited experience most utility engines, like small motorbike ones, are chronically under-cooled, so they run at temperatures far from the most efficient, or reliable.

    On balance however, for those liquid-cooled engines there is a greater parasitic load on the engine to drive the required pumps, as well as a higher system weight and complexity. As the liquid-cooled engines operate more efficiently, they can make up for that parasitic loss, particularly in providing a longer engine life and more reliable operation. The weight and complexity is a wholly different discussion, mainly about fitting the engine to the purpose it will be used for.

    Finally, and for completeness, some small engines just use a thermosyphon water-cooling system – with a large radiator mounted well above the engine, and no pump. This is a system relying on the hot water rising through the system, to where the radiator cools it, on-going heat from the engine keeps the water rising and so cycling through the system. These can be seen on many of the old 50cc GP racing bikes (like the Jamarthi and Kreidler) that did everything to keep down the parasitic losses to the engine. But great care is needed to size the system correctly, to ensure smooth paths for the liquid and a good air flow for proper cooling of the radiator.

  7. Guys I’m doing a research on engines of bikes,I was planning to use water as coolant for the engines,is there any bike that uses water as coolant,or what should I take into consideration,when I use water in a liquid coolant engine?


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