1965 E-Type - While cranking engine, before it starts, the header tank will over pressurize and start to release fluid through the overflow. Never seen this before. Ideas?

 

Hi Jerjag64,
Sorry to hear about your trouble. Does it stop over pressurizing the header tank when it warm-up? Or haven't you let it run that long? Is there any milky white oil on the dipstick? Does the exhaust look white and have sweet smelling to it? (I assume your are using ethylene glycol for antifreeze - it tastes and smells sweet. It's also toxic.)
My first guess is a head gasket leak from the cylinder to the cooling system. I have been told, never tried them, that a good auto parts store sells strip of paper that would detect exhaust gasses in the coolant, I believe it is or like litmus paper.
You you could try re-torque the head and adding some bars leak. I personally don't like using bar leak or other radiator sealers.

 

Thank you for your response. This is happening as I cranked the engine to start. I didn't actually allowed the engine to start after seeing this happen. Oil does look fine and there is no white residue on the header cap. I'll look into the "test papers" and try again this weekend. Thanks again Bob!

 

Blown head gasket.