Flushing the Inside
Remove the radiator cap. Depending on the motorcycle model, the radiator cap may either screw off or will need to be pushed in first to unlock it.
Place an empty catch pan under the water pump.
Unscrew the drain bolt with the proper-sized wrench. For most motorcycle models, the drain bolt is located near the header pipe at the front of the motor.
Remove the air bleeder bolt. It will most likely be located on the water pump or near the radiator cap. Allow the old antifreeze to drain into the catch pan.
Replace the bolts. Dump the antifreeze into a resealable container for disposal.
Add water to the radiator through the spout where you removed the cap.
Remove the bolts again to drain out the water. Repeat the draining and filling process until the drained water is as clear as the water you added. When finished, replace the bolts.
Pour a 50/50 mixture of antifreeze and distilled water into the radiator, using a funnel if necessary. Remove the air bleeder bolt again and start your motorcycle. This removes air pockets from the radiator and can take a few minutes; the motor must warm up enough to open the thermostat and cycle the antifreeze through the engine. Replace the air bleeder bolt and turn off the motorcycle.
Add more of the antifreeze mixture until it fills the overflow bottle to the "Full" line, which is usually about 1/3 of the bottle. Ensure you have tightened all the bolts and reattached the overflow hose if you cleaned the overflow bottle.
Washing the Outside
Fill a bucket with water and add dish washing soap.
Use a sponge to carefully wash the outside of the radiator and the rest of the motorcycle if desired. Wipe the area down gently to avoid damaging the delicate radiator fins.
Attach a spray nozzle to your hose and set it to either "Mist" or "Shower." The stream of water must be gentle.
Rinse the radiator and the rest of the motorcycle if necessary.