If you’re just getting started maintaining your motorcycle, changing its vital fluids is a great place to start. We have covered brake fluid in the past and now we turn our attention to the cooling system. As with brake fluid, your manual likely calls for changing coolant every two years. Whether its been longer than that or maybe you just picked up that new-to-you bike, its a good idea to take this on. You can easily complete it in half an hour. We lay out the tools you’ll need and the process you'll need to follow to ensure that your cooling system is running top notch on your bike.

Why Change Coolant?

Your owners manual says to do it, but why? Coolant has many properties and over time its ability to achieve them diminishes. Old coolant can become acidic over time and rather than inhibiting corrosion, it can start to cause it. This corrosion can damage a number of parts in the system including the radiator, water pump, thermostat, and radiator cap. As it does so, the system becomes less effective which can lead to overheating, a potentially devastating condition for any engine.

What Role does Coolant Play in My Bike’s Engine?

Of course, cooling is its primary purpose. Internal combustion engines aren’t terribly efficient mechanisms for transferring energy from fuel to propulsion. A majority of the energy potential in fuel is wasted in the form of heat. To ensure the combustion process is optimized, engines need to run within a specific temperature range, otherwise they become less efficient, or worse, inoperable. Most engines have an operating temperature around 185 degrees Fahrenheit. The job of the cooling system is to transfer excess thermal energy to the air around the bike. Coolant is the conduit for that purpose. Thermal energy is transferred from the hot metal engine components to the fluid and then to the air flowing through the radiator. Preventing the fluid from boiling is essential for this process to be effective. As we know, water alone boils at 212 degrees Fahrenheit. If we were using straight water and the engine generated more heat than the fluid could dissipate, the fluid would eventually change state from fluid to gas. At that point temperatures rapidly escalate because gasses lack the heat transfer properties of fluids. That is why it is necessary to increase the boiling point of the fluid we use. Chemicals in coolant, typically ethylene glycol help achieve this goal.

Water is Water, Right? Not Exactly.

Another property of plain water is its ability to corrode metal parts, basically everything your engine is made of. Layers of corrosion not only decay parts, they further inhibit cooling, both by creating a layer between the metal and coolant and by polluting the coolant with fragments. For this reason it is critical to use the correct type of water. For example, the water in my community is notoriously hard, which means it contains a lot of minerals. Unless your tap water is miraculously free of calcium and magnesium its a bad source.

How about distilled water? That contains none of the minerals that tap water does. Unfortunately, distilled water comes with its own downsides. During the distillation process minerals are stripped from the water. When this happens, they take electrons with them which leaves the water chemically imbalanced. If used in a cooling system, the water will attempt to re-balance itself, stripping electrons from the metals in your cooling system in the process. Clearly, you want those to stay in the metal. Distilled water, it turns out, is no better than tap water, just differently bad. That leaves us with one acceptable solution—pun intended.

Deionized water is similar to distilled water in one respect; it removes all of the mineral ions, but in the process it does not remove the electrons. The remaining liquid is a stable, mineral free solution, perfect for your cooling system.

Which Coolant is Right for My Motorcycle?

Firstly, deionized water is not commonly available. You’re not likely to find it a the local supermarket or parts store. You could order it online and have it delivered along with some straight coolant. You might even save a little money doing so, but there are other ways to go.

Pre-mixed coolants are a great way to make the job simple. They come with deionized water so they eliminate the need to search for the product as well as the need to mix it in the proper ratio. In my opinion, its well worth the extra few bucks, especially when we are talking about motorcycles with such small systems. A half gallon container is sufficient for most bikes out there.

coolant vs antifreeze

You may have noticed this is my first use of the word “antifreeze” and for good reason. As the name would suggest, all coolant additives aid in cooling, but not all of them will protect your system when temperatures get below 32 degrees. If there’s a chance your bike will ever experience sub-freezing temperatures you will want coolant that will substantially lower the freezing point, otherwise if allowed to freeze, the coolant will expand in volume, often loosening your engine’s freeze plugs and ruining hoses and radiators. Antifreeze reduces the coolant’s freezing point usually with chemicals called ethylene glycol or propylene glycol. Take note if you are planning a track day, many providers do not want you to use antifreeze in your bike. Be sure to check their regulations in advance. They have good reason for this. Antifreeze glycols are incredibly slippery. If they get spilled on track either due to overflow or a crash, it can create a genuine hazard for all the riders behind. Multiple riders going down is a concern. Multiple riders all going down in the same corner is catastrophic. You may need to opt for a different product for the riding season. As time has marched on, so have coolant additives. You may find bargain brands using Inorganic Acid Technology (IAT) and you should steer clear of those. While admirably intended to reduce the toxicity of coolant, their use of inorganic salts can quickly diminish and leave your cooling system vulnerable to scaling and sludge. There are also OAT formulations. Unlike the ones sold by the dude in the black hat with flowing white hair, these won’t lower your cholesterol. OAT stands for Organic Acid Technology as you may have guessed. Without the use of phosphates, silicates, or other inorganic salts, OAT eliminates all the problems associated with IAT coolants. Finally, there is HOAT or Hybrid Organic Acid Technology which pairs OAT which combines the two, creating a long lasting product with less toxicity than traditional chemicals. Don’t eat it though.

Only cooling

Products that specifically improve cooling are often called “wetters.” You can get these as supplements to your antifreeze, your water, or both. You can also get them in premixed containers. Wetters work at the boundary layer, where the coolant contacts the metal. They improve the coolant’s ability to transfer thermal energy, thereby improving the system’s abilities. I have personally been using Redline water wetter for decades as an additive to water. For the video I recorded, I chose their premixed Supercool Extreme product. I don’t have a need for antifreeze, but if I did they also have a version with that capability. Other popular products include Engine Ice which includes freeze protection, and Rislone Hy-per Cool which interestingly claims to work well with tap water.

How Do I Change My Coolant?

Your best bet is to watch the video at the top of the page. I demonstrate the process on a very common bike, the Suzuki SV650. The only tools you will need are a bucket to drain into, a wrench to loosen the drain bolt, and a funnel to help you pour the solution into the radiator and overflow reservoir. Some bikes will require you to remove body panels, so other tools are likely necessary in that case. Those will differ from bike to bike. I hope you learned a few things from this post—I know I did while researching it—and I hope you decide to take this on yourself. Let me know how it goes or if you have any questions in the comments field below.