Why Is My Motorcycle Leaking Coolant?


There are many advantages of owning a motorcycle that is water cooled including more effectively controlling the engine’s temperature and thermal efficiency. But, like most things, it also has it’s drawbacks.

Leaking coolant on a motorcycle can be incredibly frustrating, especially when you’re unsure where the leak is coming from and why it’s even happening in the first place.

Why is my motorcycle leaking coolant? There are several reasons a motorcycle will leak coolant including faulty hoses and clamps connecting the radiator and the engine as well as a faulty drain plug that has broken or become loose. A coolant leak can also be caused by punctured fins in the radiator, a weeping water pump, and pressure on the radiator cap from an overheating engine.

The cooling system on a water cooled motorcycle is a little less complex compared to the cooling system on a car, but there are still a lot of things to consider and look out for when you own a motorcycle like this. This article can help guide you through your coolant leak and teach you how to fix it.

Reasons For Leaking Coolant

Many years ago, water cooled motorcycle engines weren’t near as prevalent as they are today. It’s becoming more and more common among newer motorcycles because of how efficient the system is compared to air cooled engines.

To tell for sure if it’s a coolant leak you’re dealing with, assess the liquid you see leaking from your motorcycle. Antifreeze can come in all different colors, but the most common color you’ll see is a neon green. If you’re still unsure, try to smell it; coolant will have a distinct sweet smell that the other fluids won’t have.

The most common reason a motorcycle leaks coolant is because of a loose radiator hose. All motorcycles that have a radiator have an upper and lower hose; there’s an engine connection on the top and bottom and a radiator connection on the top and bottom. That means there are four possible failure points from the hoses coming from the radiator.

This is usually caused by the connection between the hose and radiator/engine not being tight enough. More commonly there is a metal clamp at each end of the hose to keep it fastened in place. One may have slipped off or the end could be corroded and cracked.

In addition to that, sometimes mechanics or motorcycle owners tighten those metal clamps at the end of the radiator hoses too tight. These clamps need to be tight, but don’t require to be extremely tight. Having these clamps too tight can end up tearing the hose and putting holes in them.

Another common failure point that could cause a motorcycle to leak coolant is the drain plug. Almost all radiators have a small plastic hand screw (that are pretty cheaply made) that can easily break. Sometimes they break even by turning it too tight with your hand. Overtime, these drain plugs can break down or corrode or even become loose from the constant vibration from the motorcycle.

If neither of these two common culprits are the cause of your coolant leak on your motorcycle, the next place you should investigate is the radiator itself. The radiator consists of small little tubes or fins that go throughout the whole part. Within these tubes is where the coolant runs to cool off and recirculate throughout the engine.

Since the radiator is located towards the front of the motorcycle, it’s possible that some sort of rock or road debris punctured a hole in one or more of those tubes/fins which would cause it to leak.

The next place you can check is the water pump. Water pumps are built with a small weep hole. There are fan blades inside the water pump that spin and circulate the coolant throughout your motorcycle engine. There is a small bearing in there that lets that blade spin freely and quickly. As that bearing gets worn over time, it loosens.

When the bearing becomes bad, it allows coolant to seep past through it and pass through that weep hole. It’s made this way on purpose because if a mechanic sees the water pump leaking or notice any corrosion, they can quickly know and diagnose a bad water pump. The location of the water pump varies on each motorcycle, so look in your owner’s manual to find it’s location.

It’s also possible that your motorcycle engine is overheating and is creating pressure that causes the radiator cap to leak (and possibly the coolant reservoir too if your motorcycle has one). If you suspect the leak is coming from your radiator cap, never remove the cap right after running your motorcycle. The pressure is still built up and can spew antifreeze everywhere it opened prematurely. Wait at least a half hour to remove the cap.

How To Fix Leaking Coolant

If you find yourself with a motorcycle that has a coolant leak, most of the fixes are relatively easy and inexpensive (the common reasons at least). If you’ve noticed any corrosion, cracks, or holes in the radiator hose(s), you’ll need to simply replace those. Those are usually only a couple of dollars.

Check the tightness of the clamps on the radiator hose. If they’re too tight, remove them and assess the condition of the hose they were clamped to. Again, if you notice any tears or holes, you’ll need to replace the hose altogether. Be sure to place and tighten the clamps at a reasonable tightness; don’t get them so tight that you break the hose underneath it.

New drain plugs are also inexpensive. If you noticed the leak coming from the drain plug, just replace the plug altogether instead of trying to save it. Those are also only a couple of dollars and it likely needs replacing anyway.

If those weren’t the sources of your leak, the cost to fix the leak from here on out goes up a little bit. If you’ve found the leak is coming from the radiator, you’ll need to get a new radiator altogether. It’s almost impossible to fix a punctured fin without causing more problems since they’re so small. A new radiator for a motorcycle usually ranges between $30-$100 and can easily be replaced by a beginner.

Unless you’ve replaced and dealt with a water pump before, I recommend you take your motorcycle in to a shop and have them replace it for you if that’s the issue you’re dealing with. That is not a beginner’s task and could have terrible consequences if done wrong. This will likely range between $100-$300.

Water cooled motorcycle engines are less likely to overheat than solely air cooled engines simply because it’s more efficient. But if you notice you’re leaking coolant from the radiator cap because of an overheated engine and know the cap is good, you’ll need to check a few thing about the engine itself.

First, notice how you’re riding your motorcycle. If you’re constantly in traffic in hot temperatures or constantly revving the engine, this will likely result in an overheated engine. Also make sure the engine has enough oil; oil, in a sense, also acts as a coolant throughout the engine and without it, the engine will overheat and possibly seize.

How To Prevent A Coolant Leak

Preventing a coolant leak on a motorcycle all boils down to basic maintenance. Be sure to occasionally check the status of the hoses and ensure they aren’t cracking or becoming loose.

Also occasionally check the coolant level and top it off as needed. Coolant can last a while, but a motorcycle will require an occasional top off. If not, that can cause the engine to overheat which results in losing more coolant.

A water cooled motorcycle should get a radiator flush about every 30,000 miles or every five years, whichever comes first. This isn’t very often you’ll need to do this, but don’t skip it once it’s time to do it.

The Consequences If Left Unchecked

A coolant leaking motorcycle should never be ignored and should be promptly attended to. Coolant for a water cooled engine is just as important as the oil that runs through it. There can be serious consequences if this issue is left unchecked.

Obviously, when a motorcycle leaks coolant, that means there is less coolant circulating throughout the engine to cool it off. It can get to a point where there simply isn’t enough coolant in the system to cool down the engine which will make the engine really hot.

When the engine becomes really hot, the pistons that are moving up and down in the chambers, as well as many other parts, will start fusing together because of the pressure, heat, and friction that the coolant was supposed to fight off. Ultimately, a coolant leak can lead to a seized engine. To learn more about a seized motorcycle engine, see my other article here.

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