How to Change the Coolant in a 1978 Honda CR250 – Step-by-Step Owner's Guide

Shop parts for a 1978 Honda CR250 Dirt Bike.

The 1978 Honda CR250 is an iconic motocross bike known for its robust two-stroke engine and lightweight frame. Regular coolant changes are crucial for maintaining peak engine performance and avoiding overheating during hard moto sessions. Early models like the 1978 CR250 have a simpler cooling system than modern machines, so routine maintenance is straightforward but essential for long-lasting engine health. Below is a proprietary MotoSport guide tailored to your vintage CR250.

Tools & Supplies Needed

  • Fresh, silicate-free premixed coolant (ethylene glycol based, motorcycle-specific)
  • Socket wrench set (common sizes: 8mm, 10mm)
  • Drain pan
  • Funnel
  • Shop rags or paper towels
  • New crush washer for the drain bolt (recommended)
  • Phillips head screwdriver (for radiator cap and shrouds)
  • Safety gloves and goggles

Step 1: Preparation

  • Place the bike upright on a level surface and let the engine cool completely before starting.
  • Remove the seat and side panels if needed for better access to the radiators.

Step 2: Drain the Old Coolant

  • Locate the radiator cap and coolant drain bolt. On the 1978 CR250, the drain bolt is typically found at the bottom of the water pump or lower radiator hose connection.
  • Remove the radiator cap slowly to relieve any built-up pressure.
  • Position your drain pan under the drain bolt.
  • Loosen and remove the drain bolt. Allow all coolant to completely drain from the system.
  • If equipped, disconnect the lower radiator hose to ensure total drainage.

Step 3: Inspect System Components

  • Check the condition of the drain bolt and replace the crush washer if worn.
  • Visually inspect radiator hoses for cracks or swelling and replace them if needed.
  • Wipe up any spilled coolant and ensure the cooling system is debris free.

Step 4: Reinstall Drain Bolt

  • Reinsert and tighten the drain bolt (use a new crush washer for best results). Do not overtighten – snug is sufficient for vintage components to avoid stripping threads.

Step 5: Refill with Coolant

  • Using a funnel, slowly fill the radiator with the recommended amount of fresh, premixed coolant. Consult your owner's manual for quantity (typically around 1 quart for CR models).
  • Fill until the coolant reaches the bottom of the filler neck.
  • Gently rock the bike side-to-side to help expel any trapped air from inside the radiators.

Step 6: Bleed the System

  • Leave the radiator cap off and start the engine. Let it idle for 1–2 minutes. Watch closely as air bubbles may rise from the filler neck.
  • Add additional coolant if the level drops as the system cycles out air.
  • Once air bubbles stop, turn off the bike and top off coolant again if necessary.
  • Replace and secure the radiator cap.

Step 7: Final Checks

  • Wipe off any spills. Reinstall seat, side panels, and any removed bodywork.
  • Start and warm up the engine, then let it cool down completely and recheck the coolant level, topping up as needed.
  • Inspect for leaks at the drain bolt, hoses, and radiator cap area.

Special Notes for 1978 Honda CR250 Owners

  • This era of CR250 does not have a coolant overflow reservoir – careful filling and air bleeding is especially important to prevent air pockets and overheating.
  • Avoid using automotive coolants with silicates or phosphates, as these can damage the lightweight radiator and water pump seals common to vintage Honda motocross models.
  • Always dispose of old coolant responsibly. Ethylene glycol is toxic to humans, animals, & the environment.
  • Check hoses and clamps at every coolant change – decades-old rubber is often brittle on original bikes and should be replaced with modern equivalents for reliability.

Keeping your 1978 Honda CR250's cooling system fresh is vital for protecting your hard-working two-stroke engine on the track or in the garage. Stay ahead of potential problems by scheduling coolant changes regularly, inspecting the system thoroughly, and always using the right products for your classic machine.

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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.