04 Coolant Overflowing

My 04 450 is giving me a real headache. Im not sure why, but my bike keeps shooting coolant out the overflow at the top of the radiator. It only does it when I hit the gas, but it happens hot or cold, pretty much as soon as the motor starts running. Any ideas why this might be happening? Ive heard bad cap, but Ive tried a different cap, same problem. Any insight would be greatly appreciated.

Although your cap may be new, check the seat in the radiator where the cap rubber seal sets. If it's good condition, the I would think it's compression getting into the cooling system. If it's compression getting into the cooling system, it's probably the head gasket. Before you go pulling the head off of the motor, you could pull the valve cover and loosen the head bolts and retorque them one at a time.

But take a good look at the radiator seat. Make sure it is level all the way around with no dents, low or high spots.

it need some room for air just fill it 1/2 inch over the core. Is it new to you? Did it just start doing that? Remove the cap with it running (when its cold) to see if its getting compression in the radatior

it need some room for air just fill it 1/2 inch over the core. Is it new to you? Did it just start doing that? Remove the cap with it running (when its cold) to see if its getting compression in the radatior

Yes, if you fill it to the top, as the coolant heats and expands it will push past the cap if there is no room for expansion. If it does it immediately when cold, then heat expansion isn't likely the problem. He could buy a cooling systen tester from a tool truck or auto supply. Connect it to the radiator and start the engine. If it goes to 1.1 bar right away, then that isn't normal heat expansion, it's compression.

Or just open the cap and give it some rpm to see if cylinder head gasket makes pressure. If you dont see over 2" water pillar from radiator then the gasket is fine. Dont run it too long without cap.

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