How To Flush Radiator Coolant on a Dirt Bike

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Hands holding a drain pan and draining coolant from a radiator hose on the right side of a dirt bike under the right radiator

Have you ever experienced hot steam coming out of your radiator overflow hose? It means it’s time to inspect and possibly flush the radiator coolant on your dirt bike.

Flushing the radiator coolant involves clearing space to access the main radiator hose clamps and disconnecting the main radiator hose to drain the old coolant into a drain pan. Then you reinstall the hose clamps, refill with new coolant, air out the system, and check for leaks.

Flushing the radiator coolant on a dirt bike is a simple process that usually takes less than an hour to complete. If you have any issues with overheating or have any leaks, you should check the system for leaks and flush the old coolant.

By following these four easy steps, you will be able to flush the radiator coolant like a pro!

Tools Required To Flush the Radiator Coolant

There are no special tools required to flush the old radiator coolant.

You may need to replace few of the hose clamps or hoses if you have a leak, but in most cases a new engine coolant and regular tools should suffice.

You can also use an oil drain pan or similar to catch the old coolant as it will be messy.

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Step 1: Clear Space To Access the Radiator Main Hoses

Flushing the old radiator coolant can be performed without removing the gas tank and usually without removing the exhaust head pipe on a two-stroke dirt bike.

Read also: How To Remove The Gas Tank On A Dirt Bike

However, the process will be much easier and quicker if you remove the gas tank, side plastic panels, and the head pipe so that you will be able to inspect for any leaks and also easily air out the system.

A dirt bike standing on a center stand with the seat, gas tank and plastics removed

If you simply wish to flush the old coolant, you can access the lower radiator hose and flush the coolant without having to remove the gas tank or exhaust pipe.

However, when you need to inspect for leaks or make sure the system is working properly and to make the flushing easier, we recommend removing the gas tank, side plastic panels, and the exhaust pipe in two-stroke engines for easier access.

Step 2: Flush Old Radiator Coolant Into a Drain Pan

Place the drain pan under the dirt bike so that you can catch the old coolant.

Next, open the lower hose clamp located near the right side of the engine next to the power valve. Some models may have a drain plug near where the lower radiator hose connects to the engine.

Hands holding a socket wrench and opening the right side radiator hose clamp on a dirt bike

Let the old coolant drain completely. You can also slightly rock the dirt bike left to right to get the most of the old coolant out. You can also open the fill cap so that the old coolant flows out quicker.

Hands holding a drain pan and draining coolant from a radiator hose on the right side of a dirt bike under the right radiator

The left side radiator is connected to the right side with a connecting hose, so there is no need to touch other hoses to drain the coolant completely.

Step 3: Refill With New Coolant

Reconnect the lower radiator hose and tighten the hose clamp. At this point, you can inspect all the hoses and hose clamps for any cracks or leaks and replace them if necessary.

Next, refill the system with new engine coolant. Open the fill cap and pour slowly until the you can see the coolant level reach the top of the radiator fins inside the radiator.

Next, open the small screw on top of the cylinder head slowly to release any trapped air in the system. Open it slowly until you can hear air hissing out and the coolant starts seeping through the threads. It is not necessary to open it completely since it causes coolant to leak over the engine making a smelly mess when the motor heats up.

An air release screw on the dirt bike cylinder head opened for bleeding the air from the radiator coolant system

Continue refilling the coolant until the coolant level sets at the top of the fins inside the right side radiator.

Step 4: Warm Up and Check Coolant Level

After reinstalling the gas tank and the plastic side panels, start and warm up the engine.

Wait for the engine to cool down until it is safe to open the refill cap to inspect the coolant level. If you aired it out properly, the coolant level should remain at the top of the fins.

Do not open the coolant cap while the coolant is hot and under pressure as it will spill out and burn you skin.

Read also: How To Change A Spark Plug On A Dirt Bike


When you flush the radiator coolant and replace it with fresh clean coolant, this improves the engine coolant capabilities. You can also use coolants that have much higher boiling point to prevent overheating and boiling the coolant over.

If you ride hard enduro or slow and very technical trails, boiling over can be an issue. You might want to consider installing a radiator fan to increase airflow in slow speeds. In that case, make sure to read our article is a radiator fan kit a must for your dirt bike.

Keep your bike running cool out there! And make sure to keep yourself riding cool too with our tips for the best dirt bike gear for hot weather!

Last updated: June 15th, 2022