Motorcycle leaking coolant

Motorcycle leaking coolant DEFAULT

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.


Liquid cooling of motorcycles allows the engines to produce far more power for a given size, compared to engines with air cooling. However, it also adds a bit of complexity and maintenance requirements that are often overlooked until damage is done.

The cooling system should be flushed and new coolant installed every two to five years, depending on the type of coolant (long life or standard) and the service conditions. Hoses crack and deteriorate from the inside out and should also be inspected and replaced as needed, every five to ten years, depending on condition.

Motorcycle Cooling Systems - Doctor Moto

Coolant (which should be a mixture of 50% water and 50% antifreeze) provides protection against freezing and corrosion, lubricates the water pump and raises the boiling point significantly higher than water. It can protect from freezing down to about -34 degrees F. With a 14 psi pressure cap, antifreeze brings the boiling point (of water) up from 212 degrees F at sea level pressure to about 264 degrees. Be sure to use coolant approved by your motorcycle's manufacturer. If you have to add only water in a pinch, flush the system and refill with the proper mix of antifreeze as soon as possible.

Motorcycle Cooling Systems - Doctor Moto

Overheating (Don't Lose Your...)

High temperatures strain a motorcycle’s cooling system, bringing out problems which often don't appear in cooler weather. Running hot can lead to a number of serious problems. It can cause detonation (also known as pinging or spark knock) under load, even with high-octane gas. To prevent damage, immediately ease off the throttle until the rattling noise lets up.

When a liquid-cooled engine gets hot, you may be warned by a gauge or a warning light. Never ignore overheating. Major engine damage may occur and coolant may boil out, which can burn you, or get on the rear tire causing a crash. Shut the engine down and pull over where it is safe while you allow the engine to cool off. Check to see if you can determine what went wrong, but never remove a radiator cap when the engine is hot.

Coolant Loss (How Does Fonzie act?)

Coolant can leak from just about any part of the cooling system. The most common places to leak are hoses and clamps, radiators, and water pumps in that order. Sometimes head gaskets leak too, which can contaminate the oil and damage the engine.

Motorcycle Cooling Systems - Doctor Moto

If coolant level in the overflow tank is low, look for a leak, which should leave drips, stains or puddles. It may be a loose hose clamp. More often it’s a leaky hose, which can be taped in a pinch. A pressure cap raises the coolant's boiling poin, and should be checked and replaced if suspect; but leave it loose if you are limping home with a taped-up hose.

Failed water pumps usually leak at the gasket or shaft seal. Thermostats temporarily shut off water circulation to hold coolant in the engine so it will warm up faster. They maintain a stable ideal operating temperature of between 160 degress on some engines up to about 195 degrees on others. If the thermostat is stuck shut, the coolant hose going from engine to radiator should be fairly cool to the touch. In an emergenc,y a stuck thermostat’s inner parts can be removed to get back on the road.

Motorcycle Cooling Systems - Doctor Moto

If your engine gets too hot while riding, but not necessarily at low speeds or idling, the cause may be a partially obstructed radiator. Insects, mud or leaves can clog external fins. Mineral deposits and rust (from not changing antifreeze) can clog the internal radiator passages. Sometimes you can partially drain the coolant, and look inside with a flashlight through an upper hose fitting (with hose removed).

Motorcycle Cooling Systems - Doctor Moto

If your engine runs hot only at low speed or when idling, the electric cooling fan may not be working. To check it, idle the engine until the coolant gets hot enough to activate the fan switch (usually around 210 degrees F) which should complete the circuit to the fan relay, then the relay sends 12-volts to the fan. Keep hands away from the fan blades, which can start at any moment. If the fan doesn’t work, inspect the fan and wiring for damage and check fuses.

Motorcycle Cooling Systems - Doctor Moto

Thermostatic fan switches are usually located near the bottom of the radiator. To bypass a fan switch, jumper the two wires going to it together. If that doesn’t work, try running a wire directly to the fan motor from a 12-volt source.

Motorcycle Cooling Systems - Doctor MotoMotorcycle Cooling Systems - Doctor Moto

If an engine keeps overheating, without either leaks, a clogged radiator, inoperative fan or stuck thermostat, it may have a “blown” head gasket, or cracked cylinder head or block. These usually happen due to previous overheating. If the coolant and/or oil look like a frothy milkshake, you probably have a blown head gasket. Do not continue running an engine that is overheated or has a blown head gasket. Radiator sealer should only be used in an emergency, as it may clog internal passages. Use factory approved products as soon as possible after field fixes are performed.

Motorcycle Cooling Systems - Doctor Moto
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Why is my dirt bike leaking antifreeze?

Leaking Coolant from Radiator Overflow
A faulty radiator cap or using a cap with the wrong pressure release for your bike often contributes to coolant leaking from the radiator overflow. Buy a new cap. But don't rule out overheating or a water pump head gasket leak that causes excessive chamber pressure.

Click to see full answer.

Similarly, it is asked, why is my motorcycle leaking antifreeze?

The most common reason a motorcycle leaks coolant is because of a loose radiator hose. 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.

One may also ask, how do I know if my dirt bike water pump is bad? Bad Water Pump Symptoms on a Dirt Bike or ATV

  1. Coolant dripping from bottom of clutch over.
  2. Milky oil and steam in sight glass.
  3. Water pump impeller doesn't spin.

Moreover, how do you fix a leaking dirt bike radiator?

The two main fixes to repair leaking radiators are to either weld the offending leak or use an epoxy, like JB Weld, to fill the crack or hole. The best solution will be entirely dependent on where the leak is. The easiest way I've found to locate a leak is to submerge the radiator underwater and pressurize it.

How do you pinpoint a coolant leak?

How to Find Leaks in Your Vehicle's Cooling System

  1. Look under your vehicle: Look under your vehicle in the morning to see if there's any liquid on the ground below the under-the-hood area.
  2. Check the radiator: Feel the underside of the radiator to see if it's leaking, and look around your radiator for whitish deposits or rust-colored stains.
Coolant Leak MotoVlog - Yamaha R6

How To Fix Dirt Bike Coolant Spewing Out Overflow Hose

Has coolant recently started coming out the overflow tube on your dirt bike? Do you have to refill the radiator with fluid after every ride? If you’re lucky, it’s a cheap and simple fix. But if you choose to ignore the problem, it will only get worse.

The most common reasons for a dirt bike leaking coolant from the overflow tube are:

  • There is too much pressure in the cooling system to hold the fluid
  • Bad Head Gasket
  • Warped Cylinder head
  • Bad water pump/impeller
  • Bike is overheating from riding too slow
  • Jetting is off

Can you overfill dirt bike coolant?

The short answer? Yes, anything above the main body of the radiator is overfill. However, this won’t hurt anything in the cooling system. As the coolant heats up, the excess will come out the overflow and then it will stabilize below the maximum fill line.

What if my dirt bike has an overflow reservoir?

A reservoir comes on some trail bikes (especially 4 strokes) because they are more likely to overheat and have coolant expand out of the radiator. Instead of going out the overflow tube and onto the ground, the tube goes to the reservoir so that it can be recycled back to the radiator when it cools down.

If you fill the reservoir and put too much in it, then the excess will just stay in the reservoir. If there’s another overflow hose then it will go out that.

Bottom line – it’s very unlikely to cause any damage by overfilling.

Should I add coolant to the radiator or reservoir?

If the engine is still hot from running, don’t open the radiator cap. Add coolant to the reservoir if it’s hot. Otherwise, when the engine and radiator are cool, then you should add coolant directly in the radiator.

Put A Cap On It!

The easiest problem to fix could be a faulty radiator cap. It may not be able to hold the pressure because it is worn or broken, allowing coolant to leak past it and out the overflow.

Coolant Leaking Out Overflow Tube How To Fix Dirt Bike Coolant Spewing Out Overflow Hose

Without spending any money, take a cap from another bike and put it on to see if that’s the problem. Ride around until the bike is warm, and if it doesn’t puke out any fluid, problem solved! If it does continue to spew coolant, then you know the radiator cap is not the problem.

Let The Cap Tell You

If you need to replace the radiator cap and want peace of mind in the future, install one with a temp sensor built in to it (Amazon). That way you can quickly check while out riding.

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You don’t want to be way out in the mountains or woods and have your bike overheating on you without even knowing it. Click the image below to purchase a new radiator cap from Amazon.

q? encoding=UTF8&MarketPlace=US&ASIN=B010RDEKE6&ServiceVersion=20070822&ID=AsinImage&WS=1&Format= SL250 &tag=leaking coolant 20 How To Fix Dirt Bike Coolant Spewing Out Overflow Hose

Can’t Handle The Pressure?

Another common problem that will not only cause the bike to overheat, but will over-pressurize the system is a blown head gasket. It will bring engine temps up greatly, and possibly cause the coolant to boil over. Then the engine leaking compressed air into the system just blows it out the radiator overflow because the cap cannot hold that much pressure.

Don’t Just Install A New Gasket!

Before you install a new head gasket, though, you need to check and make sure the cylinder and head are perfectly flat and not warped (usually caused by improperly torquing the bolts). If it is warped, you’ll want to take that to a machine shop and get it fixed. Putting a new gasket in with a warped cylinder/head will do you no good, so don’t ignore it!

Straighten A Warped Head DIY Version

If you want to save money, find a perfectly flat piece of glass or metal and put some 320 or 640 grit sandpaper on it. Spray some oil on the paper and then rub your warped head back on forth. It might not take much. All you’re doing is cleaning up the surface until it’s completely been sanded and straight again.

Liquid AND Air Cooling

Radiators don’t cool the engine by themselves. They NEED air to keep cool as well, so if they’re not getting any air-flow, it’s probably going to overheat the engine. A common problem that beginner and technical trail-riders have is riding too slow for long periods of time.

Coolant Recovery Tank For Security

If you have a liquid-cooled dirt bike and do a lot of trail riding at low speeds then you’re bound to run into this issue of the radiator spewing out coolant onto the ground. Even if your bike is running fine otherwise then you’re still losing that coolant every time it gets hot. Instead of losing that coolant you could install a coolant recovery tank for your dirt bike (Amazon). It’s super cheap, easy to install, and it simply works.

q? encoding=UTF8&MarketPlace=US&ASIN=B00K3BNLFW&ServiceVersion=20070822&ID=AsinImage&WS=1&Format= SL250 &tag=leaking coolant 20 How To Fix Dirt Bike Coolant Spewing Out Overflow Hose

If a radiator is all bent up or many of the fins are twisted out of shape, that will reduce air-flow to the radiators. You can usually tweak most of the fins back if you’re careful, but it’s best to get a radiator fixed by a professional if it is badly bent or smashed. To increase air-flow even more, you can get a vented front fender, or make one yourself if you have the patience.

Check Your Water Pump Propeller

A cause of overheating may be, although not as often, a broken impeller. If it’s cracked or part of it is broken off (yes, even one small piece) it won’t provide sufficient cooling to the bike. If none of the above are the problem, just pop off the water pump cover to see if the impeller is bad or if there’s corrosion.

Going to an aftermarket water pump impeller kit may help, but then you’d want to go with bigger radiators to compensate for the extra water circulation. The cooling system is kind of like an engine system. Everything has to work together in order to be efficient. Change one thing and the rest of the system doesn’t work the same.

If there’s damage to the water pump impeller, I suggest simply buying a new impeller and going on with your riding.

How to prevent coolant coming out overflow for Free

Maybe you don’t have any of these mechanical problems that are causing coolant to spew out the overflow. It could be something more simple. Click here for 3 free ways to prevent coolant coming out the overflow.

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Coolant motorcycle leaking


How to stop a coolant leak with Bar's stop leak!


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