Most motorcycle engines are internal combustion units, which generate mechanical power via various moving metal parts.
As these motor parts chug along to create power, they also manifest heat from the friction created as they rub up against each other in close quarters inside your bike’s engine cylinders.
While liquid-cooled engines rely on a combination of oil and radiator coolant fluid to stay cool, air-cooled motorcycles use the cooperation of airflow and engine oil.
Regardless of whether your motorcycle is air or liquid-cooled, an overheating engine is at risk of total failure, which makes recognizing the early symptoms of an overheating motorcycle important.
Find out if your motorcycle is overheating by scrolling down to the most common symptoms listed below!
1. Difficulty Shifting Gears
If the overheating results from using poor quality, contaminated engine oil, or if you’re running less oil than your motorcycle spec calls for, you may experience rough shifting.
- The difficulty changing gears on an overheating motorcycle is often accompanied by unusual vibrations coming from the engine and gearbox.
- If low or poor quality engine oil is the reason your motorcycle is overheating, you may be risking a scorched clutch plate, burnt cylinder lining, or seized gears.
If you conduct your oil changes, be sure to replace your engine oil with the type and rating listed in the owner’s manual for your make-and-year model motorcycle.
If you’re taking your bike to the dealership, technicians associated with your brand motto for oil services will likely use the suggested type of oil.
However, if you’re taking it to an independent mechanic, they may be using oil that works great for other bikes but isn’t intended for use on your bike’s particular engine size or type.
Using the spec oil in your motorcycle is always essential, but if your bike is air-cooled, the oil is especially critical for keeping your engine from overheating. Failing to do so will result in transmission failures and difficulty changing gears.
2. Unusual Engine Smells
In addition to the apparent increase in radiant temperature an overheating motorcycle engine generates, riders often experience intense “heat smells.”
For example, an overheating engine often smells like burning oil, which often smells like sulfur or burning gasoline. This can indicate expired oil or improper oil quality as the flash point is lower, so the oil burns faster than it’s meant to.
The smell of burning oil on an overheating motorcycle engine can also indicate an oil leak, mainly if the odor is caused by oil dripping onto a hot engine surface.
On liquid-cooled motorcycles, radiator coolant is sometimes made from ethylene glycol, which is similar to sugar on a molecular level and often smells like caramel when it burns.
Finally, if you suspect your motorcycle engine is overheating and you smell burning plastic, you may be at the point where your bike isn’t safe to operate.
The burning plastic smell on an overheating moto could be the stench of melting rubber seals and plastic valves, meaning your motorcycle may not be safe to drive until the issue is repaired.
3. Strange Motor Sounds
As an overheating motorcycle burns up its engine oil, the motor parts lose their primary source of lubrication.
Whether low oil is the cause of the overheating or merely the result of it, the resulting friction between engine parts is bound to make matters worse in no time.
Once engine parts lose their lubrication, they stiffen up and expand, causing all kinds of clicking, running, and metal-on-metal contact sounds your bike wouldn’t have made before it started overheating.
On certain liquid-cooled motorcycles, the coolant flow can become obstructed, which can cause the engine oil itself to overheat as it picks up the slack.
Overheating oil can thin out and heat the engine components, affecting their mechanics enough to cause ticking and clanking sounds to come from the engine.
4. Dip in Engine Performance and Throttle Response
If your motorcycle engine is overheating, you’ll notice a lag in engine performance and reliability. You may even experience frequent stall outs while riding.
While airflow is crucial to cool air-cooled motorcycles, any combustion-based engine system uses cold air to sustain its running process.
Consistent intake of cold air fuels your motorcycle’s momentum and is an integral part of your bike’s throttle response and acceleration.
Therefore, if your motorcycle is overheating, the air being pulled in starts to heat up, and hot air is less dense than cold air.
Once the hot air decreases in density, your motorcycle’s air-fuel mixture starts running rich, hurting the bike’s overall performance.
- Air intake ratio to fuel is accounted for during the engineering process, as air and fuel are equally crucial to combustion.
- When we say the air-fuel ratio is running rich, we mean there is more fuel to air than your engine requires for optimal performance.
- Running lean implies the opposite—your bike’s engine has more air than it needs and insufficient fuel.
Whether your motorcycle’s air-fuel ratio is running too lean or too rich, an improper air-fuel ratio is the most common reason a motorcycle overheats.
Therefore, a dip in engine performance and throttle response is the most common sign of an overheating motorcycle engine.
5. Reduction in Acceleration
The pistons on an overheating motorcycle engine’s cylinder start expanding, as most metals expand when they heat up.
Once they expand, the reduction in negative space limits the rotation functioning of the bike’s crankshaft.
An overheating engine’s limiting effect on its crankshaft impairs its ability to generate as much force as usual, reducing the bike’s acceleration in the process. In some cases, the cycle will take longer to accelerate; in others, the bike’s top speed will be noticeably reduced.
6. Steam or Vapor Coming From Radiator
Suppose your liquid-cooled motorcycle has steam or vapor coming from it during engine operation. In that case, it’s likely coolant boiling in the reservoir and could be a symptom of an overheating motorcycle engine.
In some situations, the problem is a failed radiator cap restricting the coolant into the reservoir by inhibiting its circulation.
If the flow of coolant is restricted on a liquid-cooled motorcycle, the engine will overheat. The excess heat causes the trapped coolant to boil in the reservoir and vaporize into steam to escape the radiator.
- Radiator fluid is a combination of water, antifreeze agents, and corrosion inhibitors.
- Therefore, depending on the ratio, the coolant will start to boil if it reaches a temperature between 223 and 260 degrees Fahrenheit.
- Since the average operating temperature of a motorcycle is between 190 and 230, depending on its design, steaming coolant coming from your bike’s radiator is a sign of an overheating motorcycle engine.
Note: If you discover steam smoking from your motorcycle, pull over immediately; restricted coolant flow can cause severe engine failure to your bike, which may result in collision or injury.
7. Rising Temperature Gauge
Some modern motorcycles have a temperature gauge that reads the internal engine temperature.
Some bikes will even trigger warnings or alerts when the engine reaches an unsafe operating temperature, while others rely on the rider to check the gauge periodically while riding.
One of the first signs a motorcycle is overheating is the rise in radiant temperature from the engine, which triggers the temperature gauge to enter the red zone and indicates an overheating motorcycle engine.
If you kill the engine as soon as your thermostat gauge enters the red zone and let it cool before you start riding, you can save yourself the time, money, stress, and troubleshooting associated with some of the other items on this list.
8. Malfunctioning Radiator Fan
The motorcycle’s radiator plays a critical role in keeping its coolant at the ideal operating temperature on a liquid-cooled bike.
- The coolant flushes the engine and absorbs the heat before returning to the reservoir in the radiator.
- As the coolant returns to the radiator, it passes through the radiator fins and under the airflow of the radiator fan.
- The fan cools the liquid coolant before it returns to the reservoir to reset.
- The cooled liquid then flushes the engine, starting the process over again.
If your radiator fan is malfunctioning, the hot coolant isn’t cooled down upon returning to the radiator. As it repeats its process, the coolant absorbs more and more heat without ever being cooled by the fan until it loses its ability to absorb heat and cool the bike engine.
Once the coolant is no longer functional, the engine components generate friction, overheat, and expand.
A faulty radiator fan is not only a potential cause of overheating on a motorcycle engine; a burned-out fan is also a symptom of an overheating engine.
9. Leaking or Damaged Radiator
If the radiator leaks coolant, the coolant level steadily decreases during engine operation.
As the coolant level decreases, the engine heat is absorbed less and less rapidly until the remaining coolant can no longer keep up with keeping your bike’s internal motor parts cool.
If you find coolant leaking from your radiator while riding, or if you find coolant residue under your motorcycle after it’s been parked, take it as a sure sign of an overheating bike; if not now, then soon.
Related: Motorcycle Won’t Start When Hot