Motorcycle Repair: Cooling system, yamaha yz400, radiator cap

Question
Thanks Mark for taking my question.  I have a 1998 Yamaha YZ400, and I am having a problem with the cooling system.  I will fill the radiator up with water/antifreze, then start the motor and when I give it the gas, water flows out the over flow tube or vent.  The water comes out with pressure and the motor gets hot quick.  I have checked the pump, removed both radiators and looked for blockages throughout the cooling system and can not figure out what the problem is?  Hopefully I have supplied you with anough infor.  If you need more infor, please e-mail me at the address above.  Thanks again Ron

Answer
Hi Ron,

Replace the radiator cap.

Perform a pressure test of the cooling system.

Anytime the cooling system is opened to air (other than removing the cap) air enters the system. The system is designed to be air free. Air causes coolant to boil at a lower temperature. Air mustt always be purged from the system with a tool designed for such use. Mity Vac company makes the Air Evac tool for this.

AllExperts does not provide your eamil to their volunteers. That's why I ask you to include your email address with question.

Respectfully,
Mark Shively