Cooling System Maintenance

Everyone knows to check the coolant level. Fewer people know that plain water actually cools worse than a proper mix, or why the radiator cap matters just as much as the coolant itself.

Why the radiator cap does more than seal a hole

The cap doesn't just stop leaks — it holds the system under pressure, and pressure is what raises the coolant's boiling point above what it would be in an open, unpressurised system. A worn or weak cap seal can't hold that pressure, which quietly lowers the effective boiling point back down — so the system can start boiling over at a temperature that would have been completely fine with a good cap. A cap that looks fine but doesn't hold pressure is a common, easy-to-miss cause of "random" boil-overs that people otherwise blame on the coolant, the water pump, or the weather.

Why plain water is worse than people assume

"Water cools better than coolant" is a common myth. In practice, plain water has a lower boiling point than a proper coolant/water mix and offers no corrosion protection at all — it actively promotes rust and scale inside the radiators and water jacket over time, and most coolant additive packages also provide a small amount of lubrication for the water pump's seal, which plain water doesn't. If you ever have to top up with plain water in an emergency on the trail, treat it as temporary and flush back to the proper mix as soon as you're home, not as a long-term substitute.

What to check regularly

• Coolant level in the reservoir/radiator, checked cold.
• Radiators for bent or crushed fins (common after a get-off or roost from another bike) — damaged fins reduce cooling capacity.
• Hoses for cracking, sponginess, or leaks around the clamps.
• The radiator cap seal — a worn cap lowers the system's pressure rating and its boiling point.

Coolant changes

Coolant loses its corrosion-inhibiting properties over time, even if the level never drops. Many riders change it once or twice a season as routine maintenance — but always use the coolant type specified in your manual, since mixing types (or using plain water long-term) can cause corrosion inside the engine and radiators.

The idle trap: overheating without ever going fast

Radiators depend heavily on airflow, and at idle or walking pace in slow, technical terrain there's barely any — a bike that runs perfectly cool at speed can climb straight into the danger zone while you're picking through a rocky or muddy section at low revs. Blipping the throttle keeps the water pump spinning faster and moves more coolant through the system than a low idle does, which genuinely helps in these situations. If it does start running hot, never remove the cap while the engine is hot — the system is pressurised and hot coolant can boil out violently the moment that pressure is released.

Signs of a developing problem

• Coolant weeping from the overflow more than usual, or needing regular top-ups — usually a sign of a failing cap, a small leak, or the system running hotter than it should.
• A sweet smell (coolant) around the bike after a ride.
• The bike running noticeably hotter or losing power in slow, technical sections where airflow drops — a classic overheating symptom on liquid-cooled dirt bikes.

Running a 4-stroke hot repeatedly is one of the more expensive ways to shorten engine life, so treat any of the above as worth investigating promptly rather than waiting for the next service.