Turn it off.

An idling engine is a hot engine and if left running too long without adequate airflow overheating usually results. Overheating is the most common problem affecting a dirt bike's cooling system but it's always the symptom of something else gone wrong.

Cooling system troubles rise from a number of issues many a result of poor maintenance. Coolant spraying from the radiator cap or spilling out the overflow tube is a tell-tale sign of an overheated engine. You'll smell it and the steam is a dead giveaway too. That said, preventing these problems occurs through routine maintenance and keeping an eye on engine temperature. However, sometimes it's completely out of your hands but with a bit of preparation you can prevent further damage or even the need for a complete engine tear down.

What coolant you choose to pour into the radiator goes a long way towards optimum cooling performance but don't think that a fresh bottle every now and then completes the maintenance cycle. Corrosion, a bad water pump and even a blown head gasket or cracked cylinder drastically affect the cooling system. Check out these common dirt bike cooling system problem you'll eventually experience and what to do about them.


When the radiator fails to properly cool the engine, overheating occurs. You could argue overheating is the umbrella affect to everything else - if something goes wrong expect overheating shortly after. The following all contribute to dirt bike engines overheating:

  • Engine idling for prolonged periods of time
  • Bad coolant in quality or age
  • Leaky radiator
  • Bad Water Pump
  • Failed internal engine parts

Catching an overheated engine is vital in preventing further damage to the cooling system and internal engine parts. But, determining engine temperature isn't exactly like opening the oven and popping in a thermometer to see if dinner is done. However, several temperature sensors exist that let you know when the engine is too hot.

The Water Temperature Sensor and Computer Kit from Trail Tech work best for trail riders (this would not be applicable in MX). An inexpensive route that works for racing is a Temperature Sticker that affixes on the outside of the engine and provides temperature ranges cluing you in on pending trouble.

Monitoring the engine's temperature is good practice anyway but let's focus on how to prevent an overheated engine in the first place.

Idling Engine

The radiator requires air flow to keep the engine cool therefore letting the engine idle while talking to your friends after an awesome stretch of trail riding or to just take a break is an easy way to overheat it. Learn to shut off the motor if you're not expecting to continue riding within a minute or so.

If overheating is a regular problem or simply not enough air circulates through the radiator try equipping your bike with an aftermarket fan.

Bad Coolant

You change the oil, so change the coolant. Follow recommended service intervals and use a high quality coolant. Just like oil, time and use degrade the protective qualities contained in coolant specifically for overheating. Use fresh coolant that meets or exceeds manufacturer's specifications. All coolant MotoSport sells meets those criteria.

It's also a good idea to routinely flush the coolant system. This cleans the system by removing corrosion which can affect seals and other components. Check out How To Flush A Radiator for information.

Radiator Leak

Crashes, wear and tear, and improper maintenance all contribute to radiator leaks. Replace damaged or leaking radiators and hoses. Alternatively, weak radiator caps leak. Replacing the stock cap with one manufactured to withstand higher pressure prevents a blow-out. However, it's essential you keep an eye on engine temperature because of the greater chance of overheating.

Clogged Radiator

Crashes, wear and tear, and improper maintenance all contribute to a clogged radiator. So does mud. Internal obstructions from a crash or roost that bends or dents the radiator, or the accrual of debris and corrosion from bad maintenance, prevent the flow of coolant. Mud, dirt and even bugs stick to the outside of the radiator preventing the flow of air.

Adding radiator protection helps prevent leaks and clogs in the event of bar-banging, a crash or mud. Prevent the build-up of mud and other debris by installing a mesh or sleeve. Add a race brace and guard to shield the radiator in the event of a crash.

Bad Water Pump

If the water pump doesn't work correctly coolant doesn't flow. But here's the chicken vs. egg - did overheating cause the water pump to fail or did the failing water pump cause overheating. Actually, it's both. Excessive overheating degrades water pump components so does improper maintenance which contributes to overheating by producing corrosion which affects pump seals. Dirty coolant affects water pump parts, as well. It all boils down to one vicious cycle!

Further, worn out water pump components (from age or bad maintenance) eventually leak thus contributing to overheating problems. As you can see, staying on top of maintenance resolves many overheating issues by allowing the cooling system to work properly.

Internal Engine Parts

Sometimes, overheating issues stem from failed engine parts like a blown head gasket, cracked heads and cylinders, a bad piston or rod bearings. These failed parts can block the cooling passages in the engine often resulting in catastrophic engine failure. A head or rod bearings eventually wear out but a cooling system that constantly overheats and experiences high pressurization dramatically affects the longevity of these internal engine parts.

It's safe to say, a well-maintained and operating cooling system prevents a number of system failures and is crucial to the longevity of other engine components and your dirt bike. And, when ever you encounter an overheated engine - turn it off.

If you're waiting for the dirt bike engine to cool off, check out these other radiator related articles:

For more in our Common Dirt Bike Problems series, check out: