How to Change Your Motorcycle’s Coolant

If you have a liquid-cooled bike, like our trusty Z900 RS here, you should be changing your coolant out every two years or so. The base of any coolant is basically deionized water, which technically never wears out, and the ethylene or propylene glycols used in coolants are actually good for 10-12 years, but many of the other chemicals, additives, and lubricants for the cooling system’s pump and seals do eventually lose their efficacy over time and exposure to heat and air.

Regular coolant changes also gives you a chance to make sure the cooling system is sealed properly, staying clean, and is otherwise mechanically sound; for instance, not leaking, or there isn’t any oil or other contaminants from the engine in it which would indicate a bigger problem, like a failing head gasket. Also, not all coolants are created equal, and modern high quality coolants as well as various additives improve the performance of the system will keep your bike running cooler, which will help you get better performance and longevity out of your engine.

Doing the job is fairly easy, and the process is pretty much the same across most liquid-cooled metric bikes. You only need a few basic tools and supplies. I’m using our Kawasaki Z900 RS for this job, but the overall procedure has been pretty much identical on everything I’ve owned from a Honda Shadow, to a Yamaha FZ1, and even a ’79 Honda CX500.

What You’ll Need:

  • A combination or socket wrench
  • A screwdriver (maybe)
  • Pliers (or strong fingers)
  • A drain pan for the old coolant
  • Distilled water
  • A funnel
  • New coolant. I always use Engine Ice in my motorcycles, which I mix about 50/50 with Redline SuperCool WaterWetter (more on this later).

First thing we need to do is make sure we’re working on a cold engine. This job is best to perform early in the day before you’ve done any riding. If you’ve gone for a ride, let the engine cool down completely before getting started, preferably overnight. The radiator cap will be under pressure when hot, and could spray hot coolant on you if opened. It’s a mess, and burns aren’t cool (chicks don’t dig scars as much as we’re led to believe). If things are cool, you’re good to go.

Start by removing the radiator cap. In most cases, you can just push and twist the cap off, like a bottle of aspirin. On some models, like my Z900 RS, there’s the addition of a set screw that further secures the cap on the neck of the radiator, so that has to be removed before twisting off the cap.

With the radiator cap removed, the coolant will be able to flow freely when drained. Place a (clean) drain pan under the motorcycle to catch the coolant when it drains. Find the coolant drain bolt; if you don’t know where it is, it can be found by following the plumbing of your cooling system to a low point, where the pump is. Once located, remove the drain bolt, and allow the coolant to drain into the pan. Once drained, I like to clean out more of the old coolant. To do so, put the drain bolt back in, slowly pour distilled water into the radiator using a funnel, then open the drain bolt again to drain the water out. If you have an older cooling system, or one that hasn’t been changed in a long time (or perhaps you’re unsure of the last change), and want to get it extra clean, you can take it one step further and use a mix of vinegar and distilled water for the first flush, followed by a second flush of pure distilled water to remove the vinegar.

If you’re changing coolant types (ie. going from ethylene glycol to propylene glycol, or going from an OEM coolant to an aftermarket brand), you’ll also want to drain and clean your reservoir tank, which is usually located behind the engine, to the side or under the seat. While there’s not necessarily anything in the chemistry that would result in engine damage if you were to mix propylene and ethylene glycol, their heat transfer properties are different. Also, different brands use different additives, detergents, and so forth, so mixing coolants dilutes their efficacy. So it’s advisable to not mix coolants, but if you accidentally do so, it won’t make your bike explode into flames.

With your cooling system drained and clean, it’s time to return the coolant bolt, replacing the washer (if there is one) and tighten it down to spec. In the absence of a torque wrench, just keep in mind that these bolts are small and require very little torque, so gently snug will do it.

Using a funnel in the radiator neck (it should still be there from flushing the system with water), slowly refill the system with your coolant of choice. Take your time, and listen for the gurgling, which indicates the coolant flowing through the system. When it starts to gurgle, slow or stop the pouring, and allow the coolant to settle a bit in order for air bubbles to flow up and out of the system. Continue to fill the system until the coolant level reaches the indicated fill line or volume for your motorcycle. Let it settle a bit, gently rock your bike back and forth to help work out the bubbles. Top off if needed.

Now you want to get any remaining air out of the system. With the radiator cap still off, start up your bike and let it idle for a few moments. You can even give it a few revs if you want. This will work the coolant through the system, and push the remaining air up to the top. Shut off your bike and let it settle for a minute or two to let the last bit of air escape, top off the coolant if needed, then put the radiator cap back on. Top off the reservoir tank to the indicated level at this point as well.

Top off the coolant reservoir tank.

Now you’re good to go for a ride. Check the coolant level (when the engine is cool) in the radiator, as well as the reservoir tank after your next few rides to make sure everything is a-ok, and top off if needed.

Which coolant should I use?

Good question. If you’re unsure, overwhelmed by options, or don’t want to do the homework, just go with the OEM, which you can find at your respective dealership. OEM will always perform great, won’t damage your engine, and is usually fairly inexpensive.

Personally, I prefer an aftermarket coolant, specifically Engine Ice. My experience with it has been great, and it’s found its way into every liquid-cooled motorcycle I’ve ever owned. It’s a highly effective, environmentally-friendly, easy to use pre-mixed coolant and antifreeze.

While Engine Ice is great on its own, I like to boost its effectiveness by adding Redline SuperCool WaterWetter, which will keep things even cooler, keep the cooling system cleaner, and protect and lubricate the cooling system internals better, for longer system life. I’ll use anywhere from 25%-50% WaterWetter in with the Engine Ice. WaterWetter, however, is not an antifreeze. This isn’t an issue to me, as I’m able to keep my bikes in my garage, and here in Texas we only see freezing temps a handful of days out of the year at most. In a colder location or without a garage, I would use less WaterWetter, or possibly none at all, or would drain the system and replace with a pure antifreeze coolant when winter rolls around.

Super duo: Engine Ice and Redline SuperCool WaterWetter

What Should I do with used coolant?

Also a good question. Don’t pour it down the sink, on the ground, or down a storm drain. Transfer it from the drain pan you used to some sort of sealed container, and take it to your local auto parts store. The majority offer free recycling and disposal of automotive fluids. If you’re unsure if yours does, check their website or give them a call to double check.

The step-by-step

  1. Make sure your engine is completely cool before working on the cooling system.
  2. Remove the radiator cap.
  3. Place a drain pan under the motorcycle and remove the coolant drain bolt to drain the old coolant.
  4. Put the drain bolt back in, slowly add distilled water, or a mix of water and vinegar, into the radiator, then remove the drain bolt to flush the remaining coolant out of the system.
  5. If you’re changing coolant types, drain and clean your reservoir tank.
  6. Put the drain bolt back in, and slowly pour in your preferred coolant until filled to the proper level.
  7. Start the motorcycle without the radiator cap and let it run for a moment (give it a few revs if you want) to get any bubbles in the system out. Top off the radiator if necessary.
  8. Put the radiator cap back on.
  9. Top off the reservoir tank.
  10. Check the coolant level (when the engine is cold) in the radiator and reservoir tank after your next couple of rides to make sure everything is good, and top off if needed.
  11. Dispose of your used coolant in a safe and responsible manner.

3 Comments Add yours

  1. Greg Shaw says:

    Thanks for the info. How do you get to the Z900RS resorvoir tank?

    1. Brent says:

      The cap for the reservoir tank is on the left side of the bike, behind the engine, just below the upper engine mount bracket. It’s tucked in there pretty good, so you’ll need a long funnel to fill it.

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