Combustion Gases Pressurizing Coolant System?

[almon]

Lose coolant and overheat all the time. I've noticed that when I first start the bike up from cold after about 30 seconds, coolant POURS out of the overflow tube. If I rev the motor it POURS out faster. The coolant is still cold at this point. I've changed rad cap, head and base gaskets. No visible leaks anywhere. This all started after a major piston sieze.

I have to believe engine combustion is getting into the coolant system and pressurizing it. Then the cap releases pressure into the overlfow tube.

My question is where this is happening. Head, cyclinder? How do I figure out which it is? New Cylinder is big bucks!

Bike is 01 CR250.

Thanks,
Almon

 

[KiwiBird]

Possible causes could be warped head, the neck of the radiator that the cap screws on to - check the tangs on the new cap too, waterpump seals, even a hole through to the waterjacket in the cylinder. Not that I'd suggest it BUT possible reassembly error (never say never)?

Sounds like a teardown and close inspection is needed.