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 every two years or so. It just wears out and loses effectiveness over time.

While the base of any coolant is deionized water, which technically never wears out, and the ethylene or propylene glycol used is actually good for 10-12 years, the other additives, detergents, and lubricants for the cooling system lose their efficacy over time.

Regular coolant changes also gives you a chance to give the cooling system a once-over. You can make sure things are sealed properly, staying clean, and is otherwise mechanically sound. This would mean it’s not leaking, and there isn’t any oil or other contaminants in the coolant which would indicate a bigger problem. Also, not all coolants are created equal, and modern high quality coolants improve the performance of the system, keep your bike running cooler, and will help you get better performance and longevity out of your engine.

Doing the job is fairly easy, and the process is largely the same for most liquid-cooled metric bikes. You only need a few basic tools and supplies, too.

I’m using our Kawasaki Z900 RS for this job, but the overall procedure has been virtually 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).

Setting up

First thing to do is make sure you’re working on a cold engine. 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). A cool engine means you’re good to go.

Draining the old coolant

Start by removing the radiator cap. In most cases, you can just push and twist the cap off, like opening a bottle of aspirin. On some models, like my Z900 RS, there’s the addition of a set screw that secures the cap on the neck of the radiator. If there’s a screw in the way, 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 drain pan under the motorcycle to catch the coolant when its drained. Find the coolant drain bolt; if you don’t know where it is, it can usually be found by following the plumbing of your cooling system to a low point, where the pump is. Remove the drain bolt, and allow the coolant to drain into the pan.

Flush the system

Once drained, it’s smart to flush out any of the old coolant that remains. To do so, put the drain bolt back in, pour distilled water into the radiator, then open the drain bolt again to complete the flush. With an older cooling system, or one that hasn’t been changed in a long time (or if you’re unsure of the last change), you can take it one step further with a mix of vinegar and distilled water for the first flush, followed by a second flush of pure distilled water to remove the vinegar.

Mixing coolant types?

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.

Technically there’s nothing in the chemistry that would damage your engine if propylene and ethylene glycol were mixed, but their heat transfer properties are different. Also, different brands use different additives, detergents, and so forth, so mixing coolants dilutes their efficacy. At the end of the day, it’s best to not mix coolants, but if you accidentally do so, it won’t make your bike burst into flames or anything.

Fill with the new coolant

With your cooling system drained and clean, it’s time to return the coolant bolt, 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.

Place a funnel in the radiator neck, and 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. 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. If there’s no fill line, check you service manual and pre-measure the amount of coolant you should use. Let it settle a bit to work out the bubbles. Top off if needed.

Now you want to remove any remaining air from the system. With the radiator cap still off, start up your bike and let it idle for a few moments. 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 few minutes to let the last bit of air escape. Top off the coolant if needed, and put the radiator cap back on. Finish up by filling the reservoir tank to the indicated level as well.

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.

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’ll boost its effectiveness by adding Redline SuperCool, which will keep things even cooler, keep the cooling system cleaner, and protect and lubricate the cooling system internals better, for longer system life. SuperCool is not an antifreeze, which isn’t an issue for a garage-kept motorcycle here in Texas. In the spring and summer, I’ll use SuperCool by itself. For the colder months, I’ll switch up to a ratio of 25%-50% SuperCool with the Engine Ice. If you live in a colder location or don’t have a garage, I would use less SuperCool, or possibly none at all, and would drain the system and replace with a pure antifreeze coolant when winter rolls around.

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.

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