serious overheating problem!

[Fast350ex]

My hybrid yz426 has a serious overheating problem. It uses a 250r radiator, and I have an ESR in-line temp guage. Everytime I ride it overheats to about 250 degrees F, after about 3 hard laps it boils over, but I have an overflow bottle and it squirts out the breather hole. I have tried engine ice, and liquid performance coolants with no effect. I have also tried adding too2cool additive to several differents types of weights and brands of oils which didn't work worth a $hit. My only option left is to try an oversized radiator, but i would hate to spend the dough and still have the problem.

Please, any help would be greatly appreciated.

[cr80r]

is anti freeze coming out of the bottom of the waterpump when you ride

[Fast350ex]

Nope, doesn't leak anywhere except for when it boils over.

[250rmike]

are you sure the water pump is working did it always over heat or did it just start. i would check for clogs maybe something got in there and check the water pump i dont know but it may use a plastic impeller like the cannondales did which has a tendency to melt and deteriorate causing a loss of flow

[Fast350ex]

It has always run hot, but it got worse, I did check the water pump it is working fine.

[250rmike]

then i would say that your not getting enough air flow to keep the bike cool would be my only guess

[mojavedude]

is your fan working, or something blocking the air geting to the rad.?

[Fast350ex]

Don't have a fan, but nothing is blocking airflow. I think it may be a headgasket.