Animated service guide
How to Change Dirt Bike Coolant
A dirt bike runs its coolant under pressure and close to 120 °C. Check the level only with the engine cold, look over the hoses and radiators, and change the coolant on schedule. A flush means draining it, rinsing, refilling with the right mix and getting every air bubble out.
The animated guide loads here. Every step is also written out below.
Before You Start
Tools
- Rag or towel for the cap
- Drain pan
- Socket for the drain bolt
- Torque wrench
- Funnel
- Flashlight
Parts And Supplies
- Coolant your manual names (premixed is easiest)
- Distilled water if you mix your own
- New sealing washer for the drain bolt
Safety
- Never open the radiator cap, hoses or drain on a hot engine. The coolant is under pressure and can blow out scalding hot.
- Coolant is poisonous. Keep it away from kids and pets, wipe up spills and dispose of it properly.
Step By Step
Only open it cold
Coolant runs hot and under pressure. Let the bike sit until the engine and radiators are cold to the touch before you open anything. Stand the bike upright on level ground.
Careful. Never open the radiator cap, a hose or the drain on a hot engine. KTM and Yamaha both warn that scalding coolant and steam can blow out.
Open the cap the safe way
Lay a thick rag over the cap. Turn it slowly to the first stop and wait. If any pressure is left it hisses out through the overflow. When it stops, press down and turn it off.
- Rag or towel
Check the level
Look into the filler neck with a flashlight. On most bikes the coolant should cover the radiator fins inside. If it is low, top up with the coolant your manual names. Plain water dilutes the antifreeze and corrosion protection, so use premix or mix with distilled water.
- Flashlight
- Funnel
Coolant level (engine cold) Bike Spec Source KTM / Husqvarna / GASGAS 10 mm above the fins KTM 450 SX-F 2024 owner’s manual, PDF p. 129 (bike upright, engine cold) Yamaha YZ / YZ-F Up to the max mark Yamaha YZ250F 2026 owner’s service manual, p. 3-23 Honda CRF250R / CRF450R Up to the filler neck Honda CRF250R 2025 owner’s manual, PDF p. 70 (refilling after storage) Check where your manual says to read the level. Always with the engine cold and the bike upright.
Shop tip. If you keep losing coolant, look for the cause. Wet hose ends, a weeping water pump and a damp overflow tube all show where it goes.
Check hoses, clamps and radiators
Follow every hose. Look for cracks, bulges, soft spots and kinks, and check every clamp is tight. Look at the radiators for leaks, bent fins and packed mud, because dirty fins cool less. Clean fins with water or air from the back and straighten bent ones gently.
- Flashlight
- Screwdriver for clamps
What coolant to use Bike Spec Source KTM / Husqvarna / GASGAS Silicate-free, to −25 °C KTM 450 SX-F 2024 owner’s manual, PDF p. 168 (aluminum engines, distilled water if diluting, never plain water) Yamaha YZ / YZ-F 1:1 glycol and water Yamaha YZ250F 2026 owner’s service manual, p. 3-24 (distilled water) Honda CRF250R / CRF450R Pro Honda HP Coolant Honda CRF250R 2025 owner’s manual, specifications Use a coolant made for aluminum engines, mixed as your manual says. Don’t mix different types.
Careful. Check the cap’s rubber seal too. A cap that can’t hold pressure lets the coolant boil sooner.
Drain the old coolant
With the engine cold, set a pan under the water pump. Remove the drain bolt, then take the radiator cap off so it drains fully. Coolant can gush out sideways when the cap comes off, so keep the pan close.
- Drain pan
- Socket
Drain bolt Bike Spec Source KTM / Husqvarna / GASGAS 10 Nm, new seal ring KTM 450 SX-F 2024 owner’s manual, PDF p. 130 (water pump cover screw M6) Yamaha YZ / YZ-F 10 Nm, new copper washer Yamaha YZ250F 2026 owner’s service manual, p. 3-24 Use a new sealing washer and the torque from your manual.
Flush with clean water
Yamaha’s procedure flushes the system with clean tap water before refilling. Pour it in at the filler neck and let it run out the drain until it comes out clean. KTM’s procedure just drains and refills, so follow your manual.
- Funnel
- Drain pan
Careful. Water left inside dilutes the new coolant. Drain it as fully as you can.
Refit the drain bolt
Fit the drain bolt with a new sealing washer and torque it. It threads into aluminum, so don’t lean on it.
- Torque wrench
Use the drain bolt from the table above.
Fill with the right coolant
Pour coolant in slowly at the filler neck until it covers the fins. Use the type and mix from your manual, and don’t mix different types. The capacity is a guide. The level mark is what counts.
- Funnel
Coolant capacity Bike Spec Source KTM 250/450 SX-F, 250/300 SX 0.95 L (1 qt) KTM 450 SX-F 2024 owner’s manual, PDF p. 130; same in the 250 SX-F and 250/300 SX/XC 2024 manuals Yamaha YZ250F 0.94 L Yamaha YZ250F 2026 owner’s service manual, p. 2-2 Yamaha YZ450F 1.03 L Yamaha YZ450F 2026 owner’s service manual, p. 2-2 Yamaha YZ250 (2-stroke) 1.18 L Yamaha YZ250 2026 owner’s service manual, p. 2-2 Honda CRF250R 1.04 L after draining Honda CRF250R 2025 owner’s manual, specifications Honda CRF450R 1.08 L after draining Honda CRF450R 2025 owner’s manual, specifications Check your manual for the capacity. Fill to the level mark rather than pouring in a fixed amount.
Bleed out the air
Trapped air leaves the head and water pump without coolant and causes hot spots. Some two-strokes have a bleeder screw on the cylinder head. Open it until coolant comes out with no bubbles, then close it. Otherwise run the engine a few minutes with the cap on, let it cool, and top up.
Getting the air out Bike Spec Source KTM 250/300 two-strokes Head bleeder, 10.5 Nm KTM 250/300 SX/XC 2024 owner’s manual, PDF p. 111 KTM / Husqvarna / GASGAS four-strokes Short ride, then recheck KTM 450 SX-F 2024 owner’s manual, PDF p. 130 Yamaha YZ / YZ-F Run a few minutes, recheck Yamaha YZ250F 2026 owner’s service manual, p. 3-24 Check your manual for a bleeder screw. Run the engine, let it cool and top up again.
Shop tip. Many mechanics squeeze the radiator hoses gently while filling to push trapped air up and out of the neck.
Warm it up, cool it, recheck
Fit the cap, warm the engine up, then let it cool down completely. Open the cap the safe way and check the level again, because the last air comes out on that first heat cycle. Top up if needed and log the change.
Coolant change interval Bike Spec Source KTM / Husqvarna / GASGAS, race or enduro Every 24 months KTM 250/300 SX/XC 2024 owner’s manual, PDF p. 36; same on the KTM 2026 XC-W, PDF p. 55, and 2025 450 XCF-W, PDF p. 54 Yamaha YZ / YZ-F (race) Every 2 years Yamaha YZ250F 2026 owner’s service manual, p. 3-4 Honda CRF250R / CRF450R race, CRF450X trail Every 2 years Honda CRF450R 2025 owner’s manual, PDF p. 44 (note 2); CRF450X 2025 OM, PDF p. 46 to 47 (note 2) Honda CRF450RL (on-road schedule) Every 3 years Honda CRF450RL 2025 Off-Road Handbook, PDF p. 37 Check your manual. Most dirt bike manuals say every two years.
Sources
Log It And Know When It Is Due Next
MotoMind logs engine hours and every service job with notes, parts and cost, and shows each task as upcoming, due or overdue. Available to download on iOS.
