We know the feeling; you start your motorcycle and rip down the block, only to smell coolant as soon as it gets hot.
Or maybe you haven’t even started your engines yet. Perhaps you walked up to the sitting bike in your garage, and the stench of liquid engine coolant is sweet in the air.
Whether you smell it while riding or smell it while the bike is parked, undiagnosed strange odors can be alarming, leaving more than a few riders asking themselves, why do our motorcycles smell like coolant?
Here’s the short answer to why your motorcycle smells like coolant:
The most common reason a motorcycle smells like a coolant is loose or broken radiator hose clamps, leaks in the radiator hose, coolant system tubes, coolant reservoir, or a failing water pump. If coolant leaks onto the engine, it will smell burnt once the motor heats up.
Is it Normal for Motorcycles to Smell like Coolant?
Motorcycles shouldn’t smell like coolant, as liquid-cooled engines are sealed. If the coolant smell is accompanied by coolant dripping on the ground, you have a leak either in your radiator from the house or due to a loose or failing hose clamp.
In some cases, however, riders report smelling that sweet smell of coolant while riding, which could result from an internal hose or tube in your coolant system leaking, generating the coolant smell once it starts to cook onto the surface of your engine cylinder.
That said, just because you’re not finding coolant on the ground doesn’t mean the stench-causing leak is definitely internal.
Some riders find they indeed have an external coolant leak, but the coolant is dripping onto their exhaust and burning up while they’re riding; the sweet coolant smell described is the smell of the liquid coolant turning to vapor as it steams off of the exhaust pipe.
If this is the case, you might be able to find burnt liquid marks or even sticky burnt residue on your pipes after riding.
In other cases, the coolant smell only happens while the motorcycle is hot. This is because the viscosity of the coolant is thicker when it’s cold.
- If the coolant system punctures are fine enough, the coolant could be too thick to escape when the bike is cold.
- Once the engine is warmed, the coolant thins out and can escape, burning and vaporizing due to both the surface and residual engine heat.
In scenarios where the leak is too small to allow cold coolant to drip, you won’t notice it visually, but you’ll notice the sweet smell of coolant steaming while you’re riding.
How to Check If Your Motorcycle Is Leaking Coolant
Here are steps you can take to check whether your motorcycle is leaking coolant:
1. Inspect the Ground Below Your Radiator
If there’s a big enough external break in your coolant system, the coolant will have room to drip through even when the bike is parked.
Like we said earlier, the coolant’s viscosity is thinner when it’s cold—depending on how big the leak is, the dripping may be much slower when the engine’s cold than once it’s parked after riding when the coolant is hot and thin.
2. Inspect the Coolant Level
Inspecting the bike’s coolant levels is suggested before every significant ride—that goes double if you even suspect there’s an impairment to the coolant system.
If your bike’s been leaking coolant for a while, or if the leak is severe enough, you’ll notice you’re refilling your coolant much more frequently than usual.
3. Check If Your Motorcycle Engine Is Overheating
If your coolant leaks before it gets where it needs to go, the first sign will be the dip in your coolant level described above.
If the coolant is leaking before it gets where it needs to go to perform its core function of cooling the engine, the engine will overheat unless the coolant is topped off constantly or if the coolant leak is minor.
4. Inspect the Radiator
The location of the radiator on many motorcycles makes it susceptible to wear and tear from road debris.
On a long enough timeline, exposing particular bike radiator designs to harsh climates and improper sitting/storage can cause corrosion.
If left unchecked, corrosion can eat through the metal radiator.
If you find damage, corrosion, or dried/burnt cooling fluid on the radiator’s surface, the radiator itself might be why your bike smells like coolant. In fact, a properly functioning radiator shouldn’t have any external coolant.
Furthermore, inspect the sealing gasket between the radiator and the coolant tank for visible damage; they wear out over time and degrade, causing leaks.
5. Inspect the Radiator Cap
Your motorcycle’s coolant system contains a significant amount of pressure to function correctly, and the radiator cap is the final seal that maintains that pressurization.
Inspect the radiator cap for any coolant to find out if you have a leak there. Also, inspect the gasket or seal around the radiator cap, as this part is suspectible to wear and lets coolant escape once it’s damaged.
6. Check for Coolant in the Engine Oil; Vice Versa
As we mentioned in the first section, some of the coolant leaks can be internal, which are the more difficult ones to detect pulled over on the side of the road.
Your moto-coolant system’s head gasket is the part that keeps the coolant out of your oil system while also keeping engine oil out of your radiator system.
If the head gaskets incur damage or corrosion, not only will you smell coolant, you’ll find coolant making its way into your oil pan and oil contaminating your coolant reservoir.
7. Check for Water Pump Failure
The water pump is the part of your motorcycle’s coolant system that circulates the coolant through your system.
The water pump is powered by your motor’s crankshaft, which is sometimes the source of coolant leaks.
If the crankshaft is failing and causing internal leaks, it’s a matter of time before your water pump stops working too.
In other cases, the water pump itself is damaged, which can generate the smell of coolant and cause coolant leaks from the pump itself.
Inspecting your water pump for proper functioning can help troubleshoot these causes simultaneously.
What Are the Causes of Coolant Leaks?
The most frequent culprit behind coolant leaks on a motorcycle is a loose radiator hose. There’s an upper and lower radiator hose on most motos.
Both hoses lead from the radiator to the engine, causing four potential points where metal expansion, damage, and loose clamps can cause coolant to seep out.
Sometimes the clamps that connect these four points come loose due to heat expanding the metal from the engine vibration.
Adversely, some mechanics over-tighten these clamps, puncturing the hose and causing leaks.
Road debris often causes damage to the radiator itself while you’re riding, which, with enough force, can put a hole in the metal. Various tubes and fins associated with your coolant system are exposed to road hazards while you ride.
Worn water pump bearings loosen over time. Coolant tends to escape past the water pump bearing by seeping through the gap created once the bearing comes loose.
Finally, an overheating engine can cause back pressure in your coolant system. Sometimes this pressure has no escape route other than to blow a hole through your coolant reservoir or blow through the seal of your radiator cap.
Once this burst of pressure release happens, the coolant has an escape route, a leak is born, and you’ll smell the scent of hot coolant while you’re riding.
How Do You Fix a Coolant Leak on a Motorcycle?
The good news is that most of the fixes associated with these leaks are cheap and easy to execute.
Radiator hoses are easily replaceable; if a hole or crack in the radiator hose is the source of your coolant leak, unclasp the clamps and replace the hose in question.
If the clamp is worn out or over-tightened, replace the clamps as well. Since it’s so cheap, I tend to replace my hoses and clamps altogether when I can afford to, as they tend to wear out in unison.
If the drain plug or plug seal is the source of your coolant leak, don’t waste your time trying to repair either one. You can replace the whole radiator plug in about five minutes for a nominal cost.
If any part of the radiator is why your bike smells like it’s leaking coolants, such as a bent fin or punctured radiator wall, we suggest replacing the entire radiator. Motorcycle radiators aren’t as costly as you might imagine, and the labor is low.
Finally, if a faulty water pump or pump bearing has a coolant leak, simply replace the whole water pump unit.
Can You Drive Your Motorcycle if Coolant Is Leaking?
You should avoid driving a motorcycle that’s leaking coolant until the leak has been repaired. On a liquid-cooled motor, coolant is as important to safe engine performance as oil and fuel.
A minor coolant leak can escalate quickly, as the coolant not only thins out when it gets hot, the leaking metal surfaces start to expand, and the leaking punctures let more of the thinning coolant through.
The more coolant escapes, the hotter the engine becomes. At the same time, the hotter the motor gets, the more fluid leaks out. The result can quickly become an overheating motorcycle engine.
If left unchecked for a substantial amount of time, overheating benign parts could fuse together, and the engine can seize for good.