How to Flush Motorcycle Radiator in 3 Simple Steps

How to flush your motorcycle radiator. Flushing the radiator on your motorcycle is really easy and can be done in a few simple steps. Watch our detailed how-to video.

• • Loosen the radiator cap but do not fully remove it

  • Place a bowl under the drain bolt to collect coolant

  • Remove drain bolt from the water pump

  • Empty radiator fully of coolant

  • Flush system with a 50/50 mixture of distilled water with vinegar

  • Refit drain bolt

  • Top up with antifreeze

When Should I Change Coolant in a Motorcycle?

Just like every other fluid on your motorcycle your coolant needs to be changed periodically, you need to refer to your owners manual to find out what the frequency should be for your motorcycle but every two years a good rule of thumb

If you have a race bike or your bike sees a lot of track time then we recommend you change your coolant at least once per season.

This article is a great companion tour on how to do a motorcycle track day because many track day providers and track organizations require that all glycol be removed from your motorcycles cooling system.

For many riders, the idea of flushing the cooling system sounds pretty daunting but in actuality flushing the cooling system is really no more involved than changing your engine oil.

First, what is glycol? Well, glycol provides protection from freezing as well as lubrication to the internal components of your cooling system. Most traditional antifreeze use ethylene glycol which provides excellent protection from freezing, but doesn’t really transfer heat all that well and is highly toxic.

Just two ounces of ethylene glycol are enough to cause total kidney failure and kill an average dog in a very gruesome and painful way so please be very careful when handling ethylene glycol around pets. Not only is it extremely toxic but it has a very sweet smell and tastes to it so animals are drawn to it.

The other problem with any kind of glycol and the reason why many track-day providers and race organizations and tracks don’t allow glycol is that when it’s spilled it’s every bit as slippery as oil and every bit as difficult to clean up.

I mentioned that ethylene glycol isn’t all that good at cooling, it’s actually the water in your coolant that’s doing all of the cooling but water provides virtually no lubrication and virtually zero protection from corrosion, which is why there are several non glycol-based products on the market such as water wetter liquid performance and kool-aid.

Some motorcycle engine coolants available

• • CycleLogic Engine Ice

  • EVANS Cooling Systems

  • VP RACING FUELS 2085

  • Red Line Water Wetter

  • KAWASAKI K61081-004A ALUMA COOL QT

These provide protection against corrosion and some lubrication but again like water these products provide no protection from freezing, so if it gets cold where you live you need to make sure you get this stuff out of your radiator before it freezes.

If your track-day does not have any glycol rule or you just need to replace your coolant then we highly recommend using a product that employs propylene glycol instead of ethylene glycol such as engine iced.

Propylene glycol still provides protection from freezing but is much better at trans during heat it’s better preventing corrosion breaks down much slower and is mostly non-toxic as long as you don’t ingest a whole lot of it. In fact propylene glycol is used in small amounts as a preservative in many brands of dog food, however, we still urge caution when around pets.

Whatever product you end up choosing we strongly encourage you to use a motorcycle specific coolant. The other important thing to remember is to only use pure distilled water never tap water.

The biggest reason to do this is tap water is likely to have all sorts of contaminants that will result in scale and deposits that will end up clogging and eventually ruining your cooling system.

Before we get started we’re going to need to drain out the old coolant flush and clean the system and then refill the system with our coolant of choice.

Draining the system is pretty easy but make sure your dog isn’t hanging out with you just in case you spill. Remove any and all bodywork that is blocking access to your radiator cap water pump, don’t forget to gain access to your overflow bottle.

Make sure your engine is cold to the touch then remove the cap on the overflow bottle. Next, loosen but don’t remove the radiator cap then get your funnel and catch basin ready and remove the coolant drain bolt which can almost always be found on the water pump.

If you completely remove your radiator cap water will shoot out of the drain bolt and across the room, by leaving the radiator cap on but lose the speed at which water drains will be more controlled. Depending on your bike you may need to remove the line that runs from the top of the radiator to the expansion tank in order to fully drain it.

To clean your system we’re going to use the exact same process you use to clean your coffeemaker. Mix some distilled water with vinegar at a 50/50 ratio the vinegar is just acidic enough to clean contaminants and residue without harming seals and gaskets.

Refit the drain bolt, fill the radiator and the overflow then wait several minutes for the water and the vinegar to fill all the internal passages inside the system. Before you refit the cap on the overflow bottle as well as refit the cap on the radiator.

Next, start the bike and let it run for about 10 minutes or until the engine reaches normal operating temperature. Walk away and wait for the engine to completely cool, maybe you’ll take the dog for a walk since you probably didn’t like being banished from the garage. When the bike is cool to the touch we want to go to the exact same process to remove the cleaning mixture from the motorcycle.

Again we need to stress do not open your radiator cap until your engine is completely cool, but once everything is cool you’ll need to flush out any remaining vinegar and water by pouring pure distilled water through your radiator until the water coming out of the drain bolt is clean.

Finally, it’s time to refill the bike with the coolant of choice, it is the exact same process we use to fill the bike with water and vinegar. Refit the coolant drain bolt and be sure to use a new crush washer, a new crush washer is only about 25 cents and well worth it for the extra peace of mind.

Fill the radiator and expansion tank allowing several minutes for the coolant to fill all the internal passages. Top off your expansion tank and replace both caps.

I like to squeeze the hoses to ensure I’m pushing fluid into any cavities and pushing air bubbles to the surface. Let the bike sit for a few minutes then recheck the fluid levels and top off again if necessary.

Start the engine and let it run for about 10 minutes until the coolant temperature reaches normal operating temperature then let the bike cool completely. As the bike cools air will be expelled from the system so you may need to top off your radiator and expansion tank one last time.

Thanks for visiting our website and we hope you enjoyed our how-to article You can find more maintenance tips for your motorcycle by clicking the links below.