• Motorcycle cooling systems decrypted

Our guide to help you understand the types of cooling systems and coolants available

By burning the all-hail gasoline inside the combustion chamber, motorcycles power your body and soul on two wheels. The engines heat up drastically with every explosion of the fuel creating high temperatures, and the friction between the mechanical parts also contributes to the immense amount of heat that surrounds the motor.

This has been one of the significant issues to tackle ever since the birth of motorcycles, and manufacturers have been continuously shelling out millions to engineer the best solutions to deal with it. The consistent performance of the engine and its overall life depends on the efficient cooling system it has. In this guide, we discuss the different ways motorcycle engines are kept cool to get optimum performances.

Types of engine cooling methods:

1. Air-cooled:

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Air-cooling is the simplest form of a cooling technique used by manufacturers on all older generation motorcycles and also on most of the modern ones that run on lower-capacity mills. The construction of the engine casing will feature “cooling-fins” that are designed to increases the surface area of the housing, allowing the heat to dissipate quickly while the air passes through it.

This is the most cost-effective way to maintain heating issues on low powered engines as they do not generate much heat compared to engines that rev high and ones making greater power. Air cooling is also found on some large-capacity engines that do not rev too high. However, they only work best in low-temperature conditions as they do tend to generate vast amounts of energy that could make the rider very uncomfortable in summer conditions and stop-go traffic situations.

The only downside of these engines is that they are made to run on a richer air-fuel mixture (too little air for the given quantity of fuel), making them less efficient, more polluting, and noisier than their liquid-cooled counterparts.

2. Air / oil-cooled:

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Typically such engines are all air-cooled itself but also adopt an oil-cooler to cools down the temperature of the engine oil. We know that the engine oil, apart from acting as a lubricant, carries the heat away from lubricated parts. But when the revs are higher and more heat is generated, the oil loses its viscosity and becomes thinner. This reduces the lubricating effect of the oil, which increases friction between the engine parts.

To avoid this, manufacturers equip the motor with an externally mounted oil-cooler radiator through which the high-temperature oil is piped, and is cooled down by the flowing air. The cooled oil regains its viscosity and is routed back into the engine. Such a system requires additional oil capacity and a higher flow rate through the oil pump.

Although oil-cooled systems cater to the cooling performance better than just air-cooled ones, it is not an efficient technique for high-performance engines that produce vast amounts of heat during all operating conditions. For such, there is Liquid-Cooling.

3. Liquid-Cooled:

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This type of cooling system is considered to be the most efficient and effective way to cool off a motorcycle engine and is similar to the ones found on automotive engines. The concept involves a liquid-coolant fluid circulated through internal channels or piping built within the crankcase all around the motor.

Similar to the oil-cooling setup, liquid cooling requires an externally mounted radiator but is a much larger and complex one with a higher number of piping and additional cooling fans. The radiator pump allows the coolant to be circulated throughout the motor and carry back the heat towards the radiator to be cooled down and re-circulated back into the engine.

The fans provide additional cooling for optimum engine performance during all operating conditions. Liquid-cooled engines are quieter, more efficient, and environment-friendly in comparison to their air-cooled counterparts.

Types of Coolant fluid available:

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1. Water-based solvent:

A coolant with at least half of its volume containing water is categorized as a water-based coolant. This type of coolant is the most cost-effective cooling liquid available either in a ready-mix form or a concentrated form where we have to add water to dilute it before pouring it into the radiator. This, however, tend to have a lower boiling point and might not be suitable for cooling the engines of high-capacity mills.

Typically green in color, this solvent is devoid of Phosphates and Silicates. Therefore, it gives limited to negligible protection to the engine and radiator against corrosion and rust.

2. Waterless solvents:

These are the more expensive and sophisticated forms of hybrid coolants that may come in varying colors. These may contain silicates to protect the engine against rust and corrosion. The lifespan of such coolants are usually reasonable and does not require flushing frequently.

Since they have better boiling point than water, such coolants are more efficient to cool the engine effectively, and hence, make them ideal for high-performing engines or motorcycles that are bred on the tracks and off-road.

Properties of coolant fluid:

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1. Ready-mix coolant:

Buying a ready-mixed coolant would save you a hassle of mixing the concentrate with water. Water-based coolants usually are a ready-mixed option as they tend to use non-ionised water. Ordinary tap water may contain minerals that could cause corrosion and limescale (salt formation) in the cooling system.

2. Antifreeze protection:

Critically crucial for sub-zero temperature conditions, the coolant must have additives that don’t let the coolant freeze. Modern coolants come with antifreeze technology that would ideally work even at -24 degrees Fahrenheit or colder.

3. Anti-Corrosive protection:

Coolants also come with anti-corrosive additives without which the coolant could corrode the inner linings of the cooling jacket. Typical corrosion inhibitors present in coolants these days include silicates, phosphates, borates, and, more recently, carboxylates.

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4. High boiling point:

Safe Operating Range for most motorcycles, an operational temperature range of 155F / 68C to 220F / 104C is standard. For the engine to continually perform at these temperatures, the coolant must have a high boiling point that should read 250F or above.

5. Long service life:

The coolant over the period gets degraded and becomes acidic and hence loses its anti-corrosive and anti-freezing properties. Picking up a suitable coolant with all these properties will go a long way into improving the fuel-efficiency and prevent any mechanical failures.

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Useful tips to consider while buying a liquid-coolant:

1. Always stick with the manufacturer’s recommended liquid-coolant as they will best suit your motorcycle’s requirements for optimum performance.
2. Always refill the coolant with the recommended capacity for the system to function at its peak performance at all conditions.
3. Always buy premixed coolants as they are just way more convenient to store and use.
4. If you purchase concentrated waterless coolants, make sure you mix it with de-ionized water and not the normal tap-water since it may contain minerals that can cause corrosion.
5. Coolants containing silicates and phosphates can be harmful to the environment and parts of your motorcycle, especially if they’re manufactured from aluminum or magnesium.
6. Pick a coolant that has antifreeze and anti-corrosive properties along with a high boiling point.
7. You can use automotive engine coolants provided the coolant contains ethylene glycol antifreeze properties.
8. It is vital to replenish the liquid-coolants at least once every year or two since they can gradually corrode metal parts and become acidic.
9. Avoid changing the coolant type at every flush as the change in the chemical formulation may do bad to the system than good.
10. Be sure to check your hoses, seals, and water pumps regularly for any damage or leakage.

Here’s a video link showing you the safest way to change your engine cooling liquid:

Sagar Patil
Sagar Patil
Motorcycle industry expert since 1997! - sagar@topspeed.com
Over the years, a deeper conscience of machines moving body and soul has given him a crisp grasp over the concepts of motorcycling. A sucker for details and common sense, he loves getting his hands dirty every once in a while. His love affair with motorcycles ushers in the specialist skillset making Sagar our go-to expert for everything on two-wheels.  Read full bio
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