How to Flush Motorcycle Radiator – Detailed Video Guide

Flush your motorcycle radiator is seven simple steps.

How to flush your motorcycle radiator. Flushing the radiator on your motorcycle is straightforward 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.

It would help if you referred to your owner’s manual to find out what the frequency should be for your bike, 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 an excellent 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 no more involved than changing your engine oil.

First, what is glycol? Well, glycol protects 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 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 extraordinarily toxic, but it has a lovely smell and tastes to it, so animals are drawn to it.

The other problem with any 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 challenging to clean up.

I mentioned that ethylene glycol isn’t all that good at cooling. It’s the water in your coolant that’s doing all of the cooling.

Still, water provides virtually no lubrication and almost 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 from Amazon

These protect against corrosion and some lubrication, but again, like water, these products do not protect 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 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 protects from freezing but is much better at trans during the 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.

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 only to 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 straightforward, but make sure your dog isn’t hanging out with you just in case you spill.

Remove any 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 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 to drain it thoroughly.

To clean your system, we’re going to use the 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 lid on the radiator.

Next, start the bike and let it run for about 10 minutes, or until the engine reaches an average operating temperature.

Walk away and wait for the engine to cool completely. 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 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 cold.

Once everything has cooled down, 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 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 average operating temperature, then let the bike cool completely.

As the motorcycle 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.


Keith Mallinson has been a motorcycle enthusiast for the past 20 years. He has owned a variety of bikes during this time, ranging from sport bikes to cruisers. Keith has a passion for all things motorcycle related, including riding, maintaining, and customizing his bikes.In addition to his personal experience with motorcycles, Keith has also kept up to date with industry news and trends. He enjoys sharing his knowledge and insights with others through his motorcycle blog.When he's not out on the open road, Keith can be found tinkering in his garage, planning his next road trip, or spending time with his family.