How to Change the Oil in a 2018 KTM 125SX: The Complete Guide

Shop parts for a 2018 KTM 125SX Dirt Bike.

Changing the oil in your 2018 KTM 125SX is a crucial part of routine maintenance. Proper oil changes ensure smooth shifting, optimal clutch function, and longer engine life. This guide is proprietary to MotoSport.com and tailored specifically for the 2018 KTM 125SX, covering required tools, step-by-step instructions, and essential model-specific call-outs.

Tools & Supplies Needed

  • T-handle or ratchet set (with appropriate sockets, especially 10mm for the drain plug)
  • Torque wrench (calibrated in Newton meters or ft-lbs)
  • Oil catch pan
  • Clean funnel
  • Shop towels/rags
  • New crush washer for drain bolt
  • Replacement oil (see KTM manual for recommended type, typically around 0.8 liters of quality two-stroke gear oil)
  • Gloves (optional but recommended for cleanliness and safety)
  • Magnetic drain plug cleaner (if equipped)
  • Pliers (for snugging the filler cap)

Step-by-Step Instructions

  1. Warm Up the Engine
    Start and briefly idle your KTM 125SX. Warming the engine helps the oil flow more freely when draining. Be careful: hot oil can burn.
  2. Remove the Fill Cap
    Loosen and remove the oil fill cap. This allows air in and helps oil drain quickly and completely.
    On the 2018 KTM 125SX, the fill cap is located on the right side of the engine.
  3. Drain the Old Oil
    Place your oil catch pan under the engine. Using your t-handle or ratchet, carefully loosen the oil drain plug (10mm socket) located below the right footpeg area.
    Allow the oil to drain completely. Do not drop the plug into the oil pan.
    When draining, lean the bike slightly to the left and right to ensure all oil exits the gearbox.
  4. Inspect and Clean the Drain Plug
    If your KTM uses a magnetic drain plug, inspect and clean off any metallic debris. A small amount of dust is normal.
    Replace the crush washer with a new one to ensure proper sealing and prevent leaks.
  5. Reinstall and Torque Down the Drain Plug
    Replace the drain plug by hand to avoid cross-threading. Then use your torque wrench to tighten the drain plug to 20 Nm (14.8 ft-lbs). Overtightening can strip the engine case threads—be precise.
    Model Call-Out: The 2018 KTM 125SX drain plug is easily accessible but always torque to spec—stripped cases are costly to repair.
  6. Refill with Fresh Oil
    Insert a clean funnel into the fill hole and pour in 0.8 liters of the manufacturer-recommended oil. Avoid overfilling and allow the oil to settle.
    On the 2018 KTM 125SX, the gearbox oil is a separate system from the engine mix.
  7. Check the Oil Level
    On some 125SX models, excess oil should weep from the check bolt when full. The 2018's design typically means you fill to the recommended volume, then check with the sight window or weep/check bolt as needed.
    Model Call-Out: If your bike has an oil check bolt (lower right case), remove it briefly after filling—oil should just begin to weep from this point. If not, add oil slowly until it does. Tighten the check bolt snugly after confirmation.
  8. Reinstall and Snug the Fill Cap
    Reinstall the oil fill cap, tightening by hand, then just a touch with pliers for security.
    Model Call-Out: KTM recommends a slight additional snug with pliers so the cap doesn't vibrate loose while riding.
  9. Dispose of Old Oil
    Never pour used oil down the drain. Take the old oil to your local automotive recycling facility.
  10. Double-Check Everything
    Start the engine, let it idle, and check for leaks at both the drain plug and fill bolt. Wipe away any drips and ensure the oil level is correct after the first ride.

Model-Specific Callouts for the 2018 KTM 125SX

  • Oil Volume: 0.8 liters. Do not exceed this amount–the gearbox will weep excess oil if you surpass capacity.
  • Use Quality Gear Oil: KTM specifies a certain type and viscosity; always match what's recommended in the owner's manual for optimal clutch and transmission function.
  • Check Bolt Location: If present, the oil check/weep bolt is below the oil fill–use it to confirm proper filling but avoid over-tightening to prevent stripping.
  • Magnetic Drain Plug: Routinely check for metal debris as an early warning for internal wear–normal dust is fine, large shavings are not.
  • Crush Washers: Always replace the crush washer every oil change for leak-free operation.

Extra Tips

  • Always change oil after riding in muddy, wet, or race conditions.
  • Use only a high-quality, manufacturer-approved two-stroke gearbox oil.
  • Retorque bolts to spec after your first short ride to double-check everything is secure.

Conclusion

Regular oil changes keep your 2018 KTM 125SX running at its best. Follow these steps every 10-15 hours of ride time or after hard use. For OEM parts, high-performance oils, and trusted tools, order directly from MotoSport.com and keep your bike ready for the next set of checkered flags.

Changing oil on the KTM 125SX isn't difficult, but careful attention to detail ensures years of top performance and reliability.

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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.