How to Change the Coolant in a 1981 Suzuki RM250
Shop parts for a 1981 Suzuki RM250 Dirt Bike.
Keeping your 1981 Suzuki RM250 running cool is essential for top performance and longevity. The RM250's liquid-cooled system relies on clean, fresh coolant to protect against overheating – especially when pushing your vintage two-stroke hard on the track or trail. Here's how to properly change the coolant – plus some RM250-specific tips every owner should know.
Tools & Materials Needed
- 8 mm socket
- Drain pan
- Distilled water (for flushing)
- Fresh coolant (check your manual for specs; most RM250s use standard ethylene glycol-based premix)
- New drain plug washer (recommended)
- Clean rags
- Safety gloves & glasses
Step-by-Step Coolant Change
- Let your bike cool completely
Never open the radiator cap on a hot motor – hot coolant can spray out and cause serious burns. - Remove the radiator cap
Locate the cap at the top of the left-side radiator. - Position a drain pan
Set it beneath the water pump housing. On the RM250, the drain bolt is at the bottom of the water pump cover. - Remove the coolant drain bolt
Use your 8 mm socket to loosen the drain bolt. Be ready – coolant will flow quickly. Remove the old washer. - Flush with distilled water
Once drained, replace the bolt and pour about 500 ml of distilled water into the radiator. Reinstall the cap, run the engine briefly (1–2 minutes), then drain again. Repeat until water runs clear. Use only distilled water to avoid mineral deposits in the cooling system. - Install new drain washer & tighten bolt
Torque to 11 N&m (8.0 lbf–ft) if possible. - Add fresh coolant
Slowly pour coolant into the radiator until it reaches the bottom of the filler neck. The RM250 typically holds about 950ml (1 US quart). - Bleed air from the system
Loosen the air bleeder bolt (if fitted); watch for air bubbles to escape, then retighten. If no bleeder is present, gently rock the bike side–to–side and squeeze the radiator hoses to help dislodge trapped air. - Reinstall the radiator cap
Start the engine and let it idle with the cap on, then let it cool fully and recheck coolant level. Top off if needed. Over the next ride or heat cycle, check the reservoir to ensure the level stabilizes, topping off as necessary. - Dispose of old coolant responsibly
Take used coolant to a recycling center – never dump it outdoors.
RM250 Owner's Tips
- Vintage RM radiators are delicate – avoid over-tightening the cap or bolts to prevent cracking.
- Check your hoses for age and cracks - original rubber may be brittle. Consider replacing for reliability.
- Monitor for signs of head gasket failure – coolant consumption, milky gearbox oil, or white smoke can indicate leaks.
- The RM250 cooling system is a closed type – don't expect fast coolant level drops unless there's a leak or trapped air escaping.
Final Inspection
- With the bike cool, verify the coolant sits at the base of the filler neck.
- Look for drips or seepage at all hose connections and the drain plug.
Changing the coolant on your classic RM250 is straightforward but must be done carefully. Enjoy smoother running, better power, and longer life from your legendary two-stroke.
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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.