How to check your motorcycle cooling system and have a fun-packed summer in 2025!

Checking your motorcycle cooling system is important whenever you plan to ride, but it’s a particularly big deal in the summer when the ambient temperature is high.

Motorcycle engines are designed to operate within a temperature range that allows for maximum efficiency between all of the moving parts. At the right temperature all the clearances within the engine will be maintained, and the oil will be able to lubricate everything perfectly. Typically, the operating temperature will be between 80°C and 90°C. 

In the past, 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.

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. These include 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 cooling system, it 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’s our guide showing you how to check your motorcycle cooling system.

Keep the fins clear

Most modern bikes are water-cooled, but older bikes will be air cooled. Air-cooling is achieved by the fins around the engine. Cooling fins should be unobstructed and clean – heavy deposits of road dirt will reduce their efficiency. Allow the engine to cool then make sure they are able to do their job by using a brush and bike cleaner to remove all traces of dirt.

• Related: Best motorcycle cleaning products tried and tested

It’s not just water 

Coolant is formulated to promote both heat transfer and offer anti-corrosion properties, combined with the ability to lubricate seals etc. The liquid needs to be changed periodically to maintain efficiency of the cooling system. Check your manual for the procedure, typically undo the radiator cap, and undo the drain bolt on the water pump. 

• Bruce’s tip: Coolant should be changed every two to three years.

Give the radiator a good spray

The radiator works thanks to fast-moving air taking the heat from the coolant via fins within the structure of the radiator. Hundreds of little fins form a huge surface area but only work if they are clean. Gently spray a fine mist of water onto the back and front of the rad, and then bike cleaner. Let the cleaner dwell for a few minutes to start loosening the dirt. 

• Bruce’s tip: If the dirt is stubborn you’ll have to do several cleaning cycles.

Give it a light hose 

Rinse the cleaner off using only minimal pressure to avoid damage. Do not use a pressure washer as this easily has the power to wreck the fins. Ideally, you should rinse the cleaner off from the back of the radiator as well as the front – this will help expel the dirt and debris back out the way it come in. 

Check for lingering bugs

Once you have rinsed the radiator check the condition of the fins at the front and at the same time look out for any other debris that hasn’t been washed off. Quite often there will be large insects such as wasps jammed in the works. Remove them by washing again and maybe agitate very lightly using a soft brush.

• Related: How to remove bug splats and tar from your motorbike

Get busy with the tweezers 

On older bikes if you look closely at your radiator you will notice that some of the fins will be damaged, usually by small stones and debris flicked up from the road. The fins can be straightened out through careful use of tweezers. It’s a delicate and time-consuming task, but it will restore efficiency. 

• Bruce’s tip: Lots of bent fins? This task is easier if you take the rad out.

How are your hoses?

The radiator is the main component of the cooling system, but it is connected to the engine via hoses and clips. Make sure the clips are free from corrosion and tight if they are the Jubilee type. Hoses need to be kept clean and check that they have not been in close contact with exhausts or chaffing on bodywork. 

Top up the coolant 

Using the recommended coolant for your bike, fill the system slowly, allowing coolant to flow through and expel air as it goes in. Check with your manual for specific procedure for bleeding air. Quite often there are bolts located around the engine which need cracking open to allow trapped air out. It’s an important task. 

Check the expansion tank 

Refit anything needed to enable you to start the bike (petrol tank etc), but don’t refit panels just yet. Start the bike, let it idle up to temperature and look for leaks. Wait until the fan comes on and then switch off and let the bike cool down. Check and top up to correct level in the expansion tank, now refit bodywork and panels.