Motorcycle Repair: Yamah YZF-R6, coolant leak, radiator cap

Question
I just bought a '03 Yamaha YZF-R6 at first it wouldn't stay running when hot at idle and it overheated. Now it just overheats when your are really riding it. The mechanics at the shop are clueless as to why. They have replaced the plugs and thermostat. I had the same problem with a truck of mine (it overheated under a load) and after replacing the whole cooling system sans radiator, it ended up being a cracked block. could this be my problem? This is all being covered under warrenty, but I'd like to steer them in the right direction to get my bike back sooner. any advice would help. thanks

Answer
Hi Eric,

If the engine block was defective you would notice a coolant leak or at very least, an odor of coolant.

I suspect air is in the cooling system. If an air pocket settles around the water pump, coolant will not circulate and engine failure may result.

Cooling systems are designed to be air-free. Air lowers the boiling point of coolant (about 246 degrees F) to just above the boiling temperature of water (about 212 degrees F). The difference of a few degrees keeps engine temperature within service limits.

Anytime the cooling system is opened to air, the system must be purged of air. This requires a purging tool such as MityVac's AirEvac tool. The exceptions are simply removing the radiator cap or resivoir cap for visual inspections.

Many techs and shops don't perform the purging procedure for various reasons. It is critical to purge the system of air. Improper coolant ratio will lower the boiling temperature, too.

Respectfully,
Mark Shively