How to Change the Coolant in a 2021 Suzuki DRZ400S: Step-by-Step Guide

Shop parts for a 2021 Suzuki DRZ400S Dirt Bike.

Keeping your 2021 Suzuki DRZ400S running cool is essential, especially if you ride hard or in hot conditions. Changing the coolant is a crucial DIY task for maintenance and longevity of your engine. This guide breaks down the process, with tips specific to your DRZ400S that every owner should know.

Tools and Supplies Needed

  • Socket set (including a 10mm socket)
  • Phillips screwdriver
  • Catch pan for old coolant
  • Pre-mixed 50/50 motorcycle coolant (silicate-free, designed for aluminum engines)
  • Clean rags
  • Funnel
  • Protective gloves and eyewear

Step 1 – Remove Side Panels and Access Radiator Cap

Remove the left side cover for easier access to the radiator and coolant reservoir. Locate the small screw securing the radiator cap and remove it, then carefully remove the cap. Always do this when the engine is cool to avoid burns from pressurized hot coolant.

Step 2 – Drain the Old Coolant

  • Place your catch pan beneath the water pump cover.
  • Use a 10mm socket to remove the drain bolt from the water pump (right side of the engine).
  • Open the radiator cap fully at this stage to let the coolant flow out quickly. Allow all old coolant to fully drain.

Step 3 – Optional: Flush the System

If you are switching to a different type of coolant or it's been years since your last change, consider flushing with distilled water. Pour distilled water into the radiator, replace the drain bolt, run the engine briefly, then drain again, repeating until clear water comes out.

Step 4 – Close and Prepare to Fill

  • Reinstall the drain bolt and snug it up – be careful not to overtighten as these threads can strip easily.

Step 5 – Bleed Air and Fill With Fresh Coolant

  • On the DRZ400S, there's a bleeder screw on the water neck at the top front of the head (not all models have it). If yours does, loosen it a few turns.
  • If your left radiator has a bleeder screw, open this as well.
  • Slowly fill the right radiator with coolant. Air will begin escaping from the open bleeder screws. Once coolant flows steadily from a screw, close it gently.
  • Continue filling the radiator gradually. As air gurgles out, keep topping off.
  • Once full, gently rock the bike left and right to help dislodge any trapped air. Top off as needed.

Step 6 – Finalize and Check Levels

  • Replace and tighten the radiator cap securely.
  • Fill the overflow bottle up to the max line – about an inch of coolant is generally sufficient for the DRZ400S.

Step 7 – Heat Cycle and Re-Check

  • Start the bike and let it run at idle until it reaches operating temperature. Monitor closely to avoid overheating.
  • Shut off and let the bike cool down completely.
  • With the engine cool, open the radiator cap and check the coolant level. Top off if needed.
  • Double-check the overflow reservoir and adjust to max line if necessary.

Notes Specific to the 2021 DRZ400S

  • The DRZ400S typically does not have a thermostat, and some models may lack the water neck bleeder screw – if yours is missing, make extra effort to "burp" the system by rocking the bike gently and checking coolant levels after the first ride.
  • The aluminum radiators and water pump of this model require silicate-free coolant to prevent internal corrosion.
  • The overflow reservoir plays an important role in managing expansion and contraction of coolant; underfilling can lead to air being pulled into the system.
  • Always inspect the radiator cap and gaskets for wear; replace as needed to prevent pressure loss.

Disposal

Never pour used coolant down drains or on the ground. Take it to a proper recycling facility or hazardous waste center in your area.

Pro Tips

  • Routinely inspect cooling hoses and replace if you see swelling or cracks.
  • A motorcycle-specific coolant with anti-freeze protection is best for storage in cold climates.
  • On first rides after a coolant change, check for leaks or drops in radiator or overflow levels.

Related Shopping Categories

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Shop Radiator Hoses for a 2021 Suzuki DRZ400S 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.