426 shooting coolant

Just replaced the water pump seals on my 02 yz426 and now it shoots coolant out of the overflow under heavy load. Doesn't leak at idle or even when I rev it in neutral. Only shoots when moving with a lot of throttle. No noticeable air bubbles when idling with the cap off. No smoke coming out of the exhaust. Does this no matter whether the engine is hot or cold. Compression feels good as normal when trying to kick it without pulling the decomp lever. It seems to leak about 12-20 ounces then stops leaking.

I tried 3 different rad caps with no change.


I would be leaning toward a head gasket thats starting to go bad.

Took it to a mechanic buddy that has the tool to check if there are hydrocarbons in the coolant. Tested positive. I dropped it at a local shop for a head gasket and a piston for good measure.

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