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I have a '39 Six that runs very good but has started pushing the water out of the Radiator at road speeds. At a fast idle there are no bubbles in the water flow but when reeved up to 2-3000 the water immediately blows out. If I have the cap on it just blows around the cap. I had the radiator Rodded out and have pulled the freeze plugs and power washed the block internally, the motor temp runs about 180 until it get's low on coolant. I pulled the head and put on a new head gasket and it all seems to have been sealing. I'm at a loss
Thanks

If it's not overheating, which it doesn't sound like it is, then I would think there is communication somewhere and combustion pressure is getting into your cooling system.

Maybe a warped head? Maybe a crack in the block?

Maybe you can use an air compressor and pressure up one cylinder at time (on compression stroke) and see if you get any air in your cooling system? Just spitballing.

Hope it's something simple!

Probably a bad head gasket. Or a cracked block, but let's hope for the best.

They have cheap chemical testers for exhaust gases in the coolant, but with symptoms this obvious, I would just start to dive in.

I would first re-torque your head bolts. Note any that are not at the correct torque, and by how much.

Retorquing the head is a good suggestion. I had to retorque my head several times on my 327 after putting a new head gasket on to get it to spec. And it doesn't cost anything to retorque you head! Even if it doesn't cure it, but makes it better, you will at least know you're on the right track.