How to Change the Coolant in a 2005 Kawasaki KLX125

Shop parts for a 2005 Kawasaki KLX125 Dirt Bike.

Routine coolant maintenance is critical for keeping your 2005 Kawasaki KLX125 running smoothly, especially since this air-cooled thumper is known for its reliable, approachable performance. Changing the coolant prevents overheating, corrosion, and engine wear–key considerations for dirt bikes that see frequent off-road use. Here is a proprietary MotoSport guide to changing the coolant on your specific KLX125 model, plus tips unique to this bike.

Supplies – What You Need

  • Fresh motorcycle-approved coolant (silicate-free, suitable for aluminum engines)
  • Distilled water (for flushing if needed)
  • Drain pan
  • 10 mm & 8 mm sockets and ratchet
  • Phillips screwdriver
  • Funnel
  • Shop towels
  • Gloves & eye protection

Step 1: Prepare the Bike

  • Make sure the engine is cool before starting–never attempt to open the cooling system when hot.
  • Set your KLX125 on a level surface and secure with the kickstand or stand.
  • Clean around the radiator cap and drain plug with a towel to avoid debris entering the system.

Step 2: Remove the Seat and Side Panel

  • Use the 8 mm socket to remove the seat bolts and side panel fasteners.
  • Carefully lift off the panels to access the radiator and overflow reservoir on the left side.

Step 3: Drain the Old Coolant

  • Place a drain pan under the water pump area on the lower right side of the bike.
  • Slowly remove the radiator cap to release any residual pressure.
  • Locate the coolant drain bolt (lower water pump cover, typically 10 mm)–loosen and remove it, allow coolant to drain out fully.
  • If equipped, carefully remove the drain plug from the cylinder area to ensure a complete drain.
  • Tip: Inspect the coolant for unusual colors or debris, a sign of engine or radiator issues.

Step 4: Flush the Cooling System (Optional but Recommended)

  • Reinstall the drain bolt lightly. Pour distilled water into the radiator, let it run through, then drain again. Repeat until water runs clear.
  • This step removes any contaminants and old coolant residue.

Step 5: Reinstall Drain Bolts and Fill with New Coolant

  • Hand-tighten the drain bolts securely. Do not overtighten–the water pump cover is aluminum and can strip easily.
  • Using a funnel, slowly add your new coolant up to the base of the radiator filler neck.
  • Fill the overflow reservoir to the full marker as well.

Step 6: Bleed the System – Remove Air Pockets

  • Start the engine and let it idle with the radiator cap off (be cautious of splashing as coolant circulates).
  • Watch for air bubbles rising, and gently rev the engine a few times to help burp stubborn air out.
  • Once no more bubbles appear and the coolant level stabilizes, top off as needed.
  • Replace the radiator cap and reservoir cap.

Step 7: Final Checks

  • After running the bike and allowing it to cool fully, recheck the coolant levels–add more if necessary, as some may transfer to the overflow tank during the first heat cycle.
  • Inspect for leaks around the drain bolts and hoses.

KLX125 Model-Specific Notes

  • This KLX125 is designed with simplicity and lighter cooling demands compared to high-power motocross bikes, but is still susceptible to debris-clogged radiators and mud build-up. Pay special attention to cleaning the radiator fins when performing a coolant change.
  • The compact frame requires cautious handling of the radiator cap and overflow tank, as some clearance is tight behind panels.
  • Check the radiator hoses for cracks or brittleness–the KLX125s of this era may develop hose wear after many years of trail use.
  • Kawasaki recommends using a premium, ethylene-glycol based coolant suitable for aluminum motorcycle engines–avoid automotive coolants with silicates, as these can damage internal components.

Disposal & Care

  • Dispose of old coolant properly–it is toxic, especially to pets and wildlife. Most auto parts stores accept used coolant for recycling.
  • Keep accurate service records for your KLX125. Coolant should be changed every two years, or more often in extreme riding conditions.

Related Shopping Categories

Shop Radiators for a 2005 Kawasaki KLX125 Dirt Bike.

Shop Coolant for a 2005 Kawasaki KLX125 Dirt Bike.

Shop Temperature Sensors for a 2005 Kawasaki KLX125 Dirt Bike.

Shop Tools for a 2005 Kawasaki KLX125 Dirt Bike.

Shop Radiator Hoses for a 2005 Kawasaki KLX125 Dirt Bike.

Disclaimer: This guide is provided for general informational purposes only and is not intended to replace your motorcycle's official owner's manual. Always refer to your manufacturer's documentation for model-specific instructions, torque specifications, safety procedures, and maintenance requirements. If you are unsure or inexperienced, consider seeking assistance from a qualified mechanic or technician.