How to Flush a Motorcycle Radiator

Overheating or freezing in the motorcycle radiator is one of the leading causes of motorcycle failure. When this happens, repairs can be lengthy and costly. Flushing the motorcycle radiator regularly is highly recommended. It doesn’t take long and it will make your bike last a lot longer.

Step 1 - Draining

Depending on the make of your motorcycle, you might have to take off the fairings or the gas tank to access the radiator. Once you can reach the radiator, use a wrench to loosen the drain bolt. On some bikes, there are up to 4 drain bolts so be sure to loosen them all. Some bikes will also have an air bleeder bolt on the water pump and a few even have 2 radiators so you will need to know your machine.

Make sure you have a drain pan under the motorcycle before proceeding. Remove the radiator cap then take out all the drain bolts and the air bleeder bolt. The coolant will start to flow from under the radiator.

Step 2 - Water

Keep the drain pan in place until the coolant stops flowing then put all the bolts back in and pour water in the motorcycle radiator until it’s full. Run engine a minute to circulate water. Loosen the bolts again and drain the water. Keep doing this until the water finally flows clear.

Now you’re ready to clean out the overflow bottle. Do this by disconnecting the hose that runs from the motorcycle radiator neck to the overflow bottle. The best way to clean out the overflow bottle is to remove it although it can be difficult to take out. Keep cleaning the overflow bottle vigorously to eliminate all of the sludge from the bottom. Once the water is clear, allow it to dry fully.

Step 3 - Air

You motorcycle will probably have an air bleeder bolt. In order to drain all the air from the system, you’ll have to remove it. If you skip this step, you can end up with pockets of hot air in the system which can, in turn, leave the bike running hot or even cause cavitation that can result in engine damage.

With the air bleeder bolt out, allow the air to drain out of the water pump. When this is done, start up the engine but only allow it to run long enough for the thermostat to open so any air trapped there can escape. When you’ve done this, turn off the engine.

Step 4 - Refill

Put all the bolts back and replace the overflow bottle, making sure the connecting hoses are tightly secured. Fill the overflow bottle of the motorcycle radiator to the full line. Dispose of your old coolant responsibly.

To refill, use a mixture of 50% coolant and 50% distilled water. You should never use regular automobile antifreeze in a motorcycle radiator. Instead, look for an ethylene glycol-based coolant that has no silicates (make sure it’s marked that way). Silicates will wear down the impeller blades on a motorcycle.