Air-cooled Vs. Liquid Cooled Engines & Coolant

by | Nov 8, 2021 | Engines and Fuel System, Mechanical | 0 comments

Image by t_watanabe from Pixabay
Did you know that motorcycle engines can get as hot as 100 degrees Celsius or 212 degrees Fahrenheit?

Of course, if it gets any hotter, it can cause wear and tear on the engine and the internal components. That’s why there must be a cooling system to deal with excessive heat.

Most motorcycle engines are either air- or liquid-cooled – each one with its own pros and cons.

In this blog post, you’ll discover:

  • Differences between air-cooled vs. liquid-cooled engines – how they work and pros and cons of each type
  • What forced-air cooling is
  • What coolant consists of – and whether motorcycle coolant is the same as car coolant

Quicklinks:

Prefer to get this information in podcast form? Listen to the 30 Minute Motorcycling Podcast episode about air-cooled and liquid-cooled engines:

What’s an air-cooled engine, and how does it work?

image of an aircooled engine for a motorcycle
Image by 2427999 from Pixabay
An air-cooled engine is easily distinguishable by a series of fin-shaped vents on the cylinders. As you ride, the airflow will enter the engine through these vents and cool down the engine.  

Some powerful engines use an air and oil cooling system, where the oil is sprayed onto the bottom of the piston crowns by small jets.

Benefits of air-cooled engines

The most significant advantage of air-cooled engines is that they are very lightweight. They also require very little maintenance. 

It’s therefore common to see air-cooled engines on small mopeds and motorcycles.

Disadvantages of air-cooled engines

An air-cooled engine is only cooled if there’s air going into it, which only happens while you’re moving. So with that in mind, what do you think happens when you’re standing still at e.g. a stoplight? 

The engine’s still running, but since you’re not moving, there’s no air going into the vents on the engine – therefore, the engine isn’t cooled. 

Furthermore, since the air temperature can vary, so can the cooling. For example, on a really hot day, the engine will receive hot air while you’re riding, which isn’t as effective as cold air.

Forced air-cooling

To address the key flaw of an air-cooled engine, some engines use a system known as “forced air-cooling.” 

Forced air-cooling means that the engine has a fan inside which is run by power from the engine.

However, while this gives a more stable cooling, engine power is lost, since the engine has to provide power to the fan – which also adds extra weight to the bike.

Fake Air-Cooling?

Some riders prefer the look of an air-cooled engine so much so that some manufacturers make engines that have the fins on the engine – just like a regular air-cooled engine. 

However, underneath, the engine is actually a liquid-cooled engine, with its radiator cleverly disguised. 

What is liquid cooling?

Liquid-cooled engines use a special liquid known as “coolant” to cool down and is by far the most common engine cooling system for most modern motorcycles. 

The coolant is circulated through the engine through a water jacket, which cools off the cylinders by dosing the hot parts.

In addition to this, the coolant is also responsible for preventing corrosion and lubricating the water pump among other things.

Benefits of liquid-cooling

Liquid-cooling doesn’t rely on whether you’re moving or not – as long as the coolant circulates properly, the engine is always cooled. It also reduces much of the engine’s noise.

Disadvantages of liquid cooling

A liquid-cooled engine has a higher running cost compared to an air-cooled engine. The coolant itself must be bought separately, topped up every now and then, and even flushed once every two years.

 

Since a liquid-cooled system also needs components like a water pump and a water jacket, the overall weight of the bike also increases.

Now that we’ve covered the differences between air-cooled vs. liquid-cooled engines, let’s briefly talk about coolant.

What is “coolant” and what’s in it?

Coolant consists of 50% distilled water and 50% anti-freeze – the latter of which consists of glycol.

What is anti-freeze for?

In colder parts of the world (e.g., Canada, Midwestern USA, and Norway), the coolant would freeze during the winter if it was 100% water.

And if the coolant freezes, not only will it not do its job, but it can also cause damage to the engine itself.

Therefore, the anti-freeze lowers the freezing point. A standard mixture of 50% water and 50% anti-freeze has a freezing point of -33 Celcius or -27 Fahrenheit.

However, with a mixture of 60% anti-freeze and 40%, it’s possible to get a freezing point as low as -38 degrees Celcius or -36 degrees Fahrenheit.

Coolant FAQs

Is Motorcycle Coolant The Same as Car Coolant?

Generally speaking, yes. However, when buying coolant, make sure that it does not contain silicates or phosphates since these can cause the magnesium and aluminum parts to rust.

Has Your Coolant Gone Brown?

If so, you need to know that it’s bad – very bad. 

If your coolant has turned brown, it could mean that you have a blown head gasket.

Remember this saying:

“If your coolant is green, you’ve got a healthy machine. If it’s milkshake brown, you’re in blown head gasket town”

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