Why Is My 4 Stroke Dirt Bike Overheating?

Is your 4 stroke dirt bike overheating? Does it lose power or have coolant coming out the overflow hose?

There’s several causes and symptoms of an overheating 4 stroke dirt bike. We’ll look at how it happens and how to fix it prevent it.

What Does Overheating A Dirt Bike Mean?

A proper operating temperature for a 4 stroke dirt bike is between 180 and 220 degrees Fahrenheit. Temperatures hotter than that means that the engine is overheating and damage will happen sooner than later.

How To Tell If A Dirt Bike Is Overheating

The most common signs that a dirt bike is overheating are:

  • Coolant coming out of the overflow
  • Bike is steaming
  • Coolant is burning (smells sweet)
  • Loss of power
  • Oil Leaking from seals
  • Cylinder/engine case is hotter than normal
  • Engine locked up and won’t turn over

There are different reasons why your dirt bike may be overheating. Some of them are because of a problem with your bike, but it may just be a cause that can be remedied with a simple fix.

The Most Common Reasons Why Your 4 Stroke Dirt Bike Is Overheating:

  • Low coolant
  • Bad radiator cap
  • Blown head gasket
  • Bad water pump
  • Jetting is too lean
  • Riding Too Slow

Before you do anything, there is one thing you should check that some riders choose to ignore. Coolant flows through the engine to keep your bike running ‘cool’. If there’s little to no fluid, it’s just going to overheat.

Low Coolant?

Before every ride, pop the cap off the radiator to check and make sure it’s full of coolant. Just by doing this you can prevent a costly engine repair.

Coolant Leaking Out Overflow Tube Why Is My 4 Stroke Dirt Bike Overheating?
Low Coolant

On the other hand, if you keep having to fill the radiator because the coolant level is down after every ride, then you have problems. There is a leak somewhere, and you’ll have to take stuff apart to find it. It will often be a blown gasket (base, head, or water pump), a hole in the radiator, or in a hose.

Coolant Coming Out Of The Overflow?

Your dirt bike may be losing coolant out of the overflow for a few reasons. As mentioned above, a blown head gasket is a common sign of coolant coming out of the overflow hose. A bad or leaking radiator cap can allow coolant to leak by, or the engine will simply get too hot and boil it out.

Instead of waiting until this happens when riding, you can simply add a radiator cap with a temp sensor (Amazon) on it. That way you can quickly check it while riding to see if the coolant is getting too hot.

Click the image below to buy a cap for your dirt bike.

q? encoding=UTF8&MarketPlace=US&ASIN=B010RDEKE6&ServiceVersion=20070822&ID=AsinImage&WS=1&Format= SL250 &tag=dirt bike overheating 20 Why Is My 4 Stroke Dirt Bike Overheating?

Did You Blow A Gasket??

That brings us to the next possible culprit. A worn or torn gasket will allow coolant to seep through, reducing cooling, and very possibly causing damage.

The Water Pump

The least damaging can be the water pump seal/gasket. If you’re lucky, it will just dribble out somewhere around the impeller cover and onto the ground. It can also mix with the tranny oil, causing it to corrode and eventually seize. If that is the problem, it’s best to replace it right away.

The Head Gasket

A blown head gasket can be a cheap fix, but it could also cause an engine malfunction. If you’re running your bike with a bad head gasket, it’s probably burning coolant, which will show up as white smoke out the exhaust.

Hopefully Not A Base Gasket

A faulty base gasket is usually going to be worse. Coolant will leak into the transmission, contaminating the oil. This will eventually cause it to fail, or the piston/cylinder will overheat and seize due to the lack of coolant in the radiators. It can also happen in a matter of hours or even minutes.

Inspecting Can Save You Money

This is why it’s always a good idea to take the top-end of an engine off (if it’s a used bike you bought) to see if anything needs replacing, or if something was put in wrong by the previous owner (happens WAY too often, so don’t ever think it won’t happen to you!).

Lean Jetting Will Burn Your Engine Down

Tuning a dirt bike carb to find the right jetting is important for so many reasons. A finely tuned carb will provide better power, throttle response, fuel mileage, and reliability.

Jetting that is too rich will cause your dirt bike to sputter, bog, and run poorly. It will also leave more unburnt fuel deposits (the crusty black stuff) on the piston, exhaust chamber, ports, as well as the inside of the exhaust system.

A lean running engine doesn’t have enough to burn, so it starts burning the metal around it because it’s a hotter combustion. Leaving the jetting too lean for too long will overheatt and burn the piston and/or valves down.

Radiators Need Air To Cool As Well…

The other common factor of overheating is not one that everyone realizes. Water isn’t the only thing that keeps a bike cooled. Air is still needed to flow past the radiators to keep the radiator temps down.

So, if there’s no air-flow, then there is little cooling. Simply put, if you’re idling or putting around a lot, your bike is going to start overheating. Not only does it get hot from little air-flow, but the little amount of gas going through the engine also causes it to get too hot.

The gas actually cools the intake and exhaust valves as it passes by, so 4-stroke motocross bikes need to be ridden fairly hard to stay cool. This is one of the major reasons why valves burn up, so don’t let your bike sit and idle for very long (How To Properly Warm-up Your Dirt Bike).

There are a few ways to fix these problems. If it’s a gasket, then pretty much the only thing to do is replace it. Improper jetting will cause problems as well. Too rich and it won’t run right at all. Too lean and it will burn the piston down. Read the Jetting 101 guide here and it will show you how to properly jet your dirt bike.

If coolant is weeping out of the overflow tube on a hot day, a simple fix to keep the temp down could be a high-performance radiator coolant. It can bring down the running temperatures by up to 50 degrees Fahrenheit. If there is nothing defective on your bike, this alone can prevent overheating problems.

Overheated Engine 2 Why Is My 4 Stroke Dirt Bike Overheating?
2-stroke piston from overheated engine (happens to 4-strokes too)

Race Gas Runs Cooler

Another way to cool a bike down is with different gas. I wouldn’t necessarily recommend this for that sole purpose, because if your bike regularly overheats then it has bigger problems. Higher octane gas, such as race-gas, will make your bike run a little cooler. Although, doing this will require re-jetting.

Higher octane gas burns at a slower rate, reducing the engine temperature. But, if you keep the previous jetting, it will be on the rich side because it’s putting more gas into the engine than it can burn. Race-gas is used by many racers to help make their bike run better (instead of nasty pump-gas), and probably cooler.

Want to know some more ways to prevent overheating for free? Click here to learn how.

Kelley Fager

I help new riders learn how to safely ride and understand how to tune and fix your dirt bike in your garage.

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