How To Flush And Service A Motorcycle’s Radiator

Summer heat isn’t just hard on you as a rider; it’s also hard on your engine. Make it a little easier by performing coolant flush and servicing the rest of the bike’s cooling system. Most owner’s manuals recommend replacing the coolant every two years. Here at MC Garage, we give you detailed instructions on how to refresh your bike’s coolant. This procedure works for most bikes, but some have very specific steps to take. Consult your manual before you begin.

First up, your bike should be cool before you crack the radiator cap. You don’t want to scald yourself. Also, most OE coolant is toxic so keep it off your hands and paint and don’t let your pets drink it. If it’s green, it’s likely made with ethylene glycol, which is poisonous. Most modern aftermarket coolants are made with non-toxic propylene glycol. Those will be colored blue or pink. Make sure that you have a sealed container nearby so that you can transport it to a disposal center when you’ve finished the job.

Before you can drain the cooling system, you’ll need to peel off whatever bodywork is necessary to get to the radiator cap, water pump, and reservoir tank. This procedure varies based on the bike, so take your time and be careful not to damage any bodywork tabs. Now is also a good time to inspect the radiator hoses for cracks or damage. Inspect the hose clamps and take a close look at the radiator itself. Use a small flat-blade screwdriver to straighten bent cooling fins.

Once everything is exposed, locate the drain plug on the water pump. It’ll have a sealing washer behind it and is usually at the lowest point on the pump cover. Position a drain pan under the bike and unscrew the drain bolt. The fluid will dribble out slowly until you crack the radiator cap, and then it’ll come pouring out. If the reservoir tank has a siphon hose or is easy to remove, drain the tank, rinse it out with fresh water and reattach.

If you notice that your coolant is extremely discolored—or you’ve neglected to change it at the appropriate service interval—go ahead and flush your radiator with a hose. With the water running through the radiator, check for cracks and hardening. Check the hose clamps for tightness, and take a look at your radiator fins again, too.

Now it’s time to refill the cooling system. Throw a fresh sealing washer on the drain bolt and then tighten it. Most motorcycle coolants come pre-mixed and ready to use, but others come as a concentrate that you have to mix yourself. Usually, it’s a 50/50 mix. Make sure to use distilled water to avoid adding any minerals or contaminants to the mix. Again, do not mix your coolant with tap water, it can leave deposits inside of the delicate fins of the radiator. Reinstall the drain bolt and pour in fresh coolant to the top of the filler neck.

Once you’ve filled up the radiator to the top of the filler neck, start the bike (with the radiator cap off) and run it for several minutes, blipping the throttle and rocking the bike gently to help free any air. This is called burping a radiator and will ensure that there are no air bubbles trapped in the cooling system. Recheck the fluid level, top it off again, fill the coolant reservoir to the upper line, and you’re good to go. Reinstall any bodywork and make sure to dispose of your old coolant at the nearest auto parts store or recycling center.