How to: Check your motorbike’s cooling system

Make sure your bike’s cooling system is working properly and won’t leave you hot under the collar

Most modern bikes rely on more than the air around them to stay cool

by Jim Blackstock |

In the old days, most bikes were air-cooled. Although that’s a bit of a misnomer; it was a combination of air and oil-cooling, with the oil being sprayed onto key components then run through a cooler as well as lubricating the motor. There is still some air (oil) cooled bike’s around, but they tend to be lower-specification machines.

Most modern bikes are liquid-cooled and for good reason. It offers the best way to remove heat energy from the engine that, if allowed to build unchecked, would cause damage to the motor – potentially catastrophic. Water is circulated throughout the engine and pumped through a heat exchanger (radiator) at the front of the engine - here it is cooled by air flowing over it, then re-circulated.

In days gone by, this would have been water with perhaps anti-freeze added so that in winter, the liquid didn’t freeze and potentially damage the engine.

However, nowadays most modern engines run on coolant, which may or may not be based on water but with a range of additives to give it certain qualities, such as lowering the freezing point below 0°C to protect the engine when cold; raising the boiling point past 100°C to do the same but at higher temperatures; and to minimise corrosion within the engine itself.

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Like any other part of the motorcycle, the cooling system needs checking and potentially maintaining from time to time. Generally, this shouldn’t mean any significant work but many manufacturers specify coolant changes during the life of the bike, perhaps every two or three years, so it obviously deteriorates over time.

Here is how you can make sure your cooling system stays in perfect shape.

Step 1:

Motorcycle coolant header tank
©Photo: Bauer Media

The first thing to do is find the coolant header tank. This is where the liquid is displaced as it expands or is pressurised during operation and where you need to check the level. On this Yamaha Tracer 900, it’s low-down on the left side of the engine.

Step 2:

Coolant tank with level indicator
©Photo: Bauer Media

The other side of the header tank is the business end. It has a plastic cover that houses the window which will help you work out what the level is.

Step 3:

Header tank collant level
©Photo: Bauer Media

On all bikes with a header tank, there will be a full and low mark. With the bike standing upright on flat ground, the level shown should ideally be halfway between the two or slightly higher. If it is getting close to the low mark, you may need to add extra coolant.

Step 4:

Yamaha Tracer coolant filler cap
©Photo: Bauer Media

On the Tracer, any coolant that needs adding goes in through the cap on top of the header tank. Simply remove the cap, add some coolant and replace the cap, making sure it is seated completely.

Step 5:

Yamalube
©Photo: Bauer Media

We would recommend following the manufacturer’s recommendations for coolant. Not surprisingly, Yamaha recommends its 'Yamalube' coolant though, in an emergency, water can be added when mixed in equal proportions with ethylene glycol antifreeze for aluminium engines, as specified in the Tracer 900 handbook.

Step 6:

Motorcycle radiator cap
©Photo: Bauer Media

Most bikes will also have a familiar radiator cap - but don’t use this. This will usually be used for refilling the cooling system when it has been flushed and the coolant changed.

Step 7:

Motorcycle radiator
©Photo: Bauer Media

If your level is unexpectedly low (i.e. dropped to the low mark in a few hundred or a couple of thousand miles) then this needs investigating to find out where it is leaking from. However, even if it has only lost a little or none at all, it never hurts to have a check around the cooling system when you’re at it or cleaning the bike. Start with the radiator and make sure it hasn’t got clogged with dirt and road debris. Gentle cleaning is key here – don’t go mad with the pressure washer.

Step 8:

Motorcycle radiator hose clip
©Photo: Bauer Media

Check the areas whether the rubber hoses meet the metal unions of the radiator for signs of coolant leaks and that the hoses haven’t begun to perish if your bike is a few years old.

Step 9:

Motorcycle water pump
©Photo: Bauer Media

Also, look around the water pump for any signs of leaks. Push-fit plastic pipes into plastic housings with rubber O-rings can eventually start to leak coolant.

Step 10:

Motorcycle thermostat housing
©Photo: Bauer Media

Check the thermostat housing on the engine block as well – this is another key area that can develop leaks over time.

Step 11:

Rubber hoses and unions in a motorcycle cooling system
©Photo: Bauer Media

Also, check the rest of the rubber hoses and unions for signs of damage, perishing or minor leaks.

Step 12:

Motorcycle radiator
©Photo: Bauer Media

Some radiators are more exposed than others. For bikes with tiny front mudguards or those that might go on the odd off-road foray, a radiator cover could be a handy investment to protect the rad from potential damage.

Step 13:

Motorcycle radiator guard
©Photo: Bauer Media

A radiator cover simply fits to the front of the rad to prevent any stones or debris that get flung up from the front wheel or other road users from damaging the fins or the core of the radiator and lead to leaks or cooling problems.

Step 14:

Radiator on a 125cc motorcycle
©Photo: Bauer Media

Even small bikes (this is a 125) have radiators nowadays and they need to be looked after just as well as their larger siblings.

Handy tools for home motorcycle mechanics:

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