Fellas thanks for the feedback, not to be a nuisance I'm trying to understand is this unique to the engine or Pontiac engines? The reason I ask is I have not had this type of situation with Chevy or Mopar engines in mid to late 60's muscle cars. Typically i would expect with cap off engine running at steady state coolant level would settle down and stay at a consistent level.

With the cap on the pressure I'm feeling in the hoses seems excessive to the point I'm a little concerned there might be a burst condition.

I'm struggling to understand what is making the coolant continually raise and fall 4-5 inches in the rad (once warmed up viewing through filler neck with cap off). Could there be a flow restriction, air bubble captured in the system, etc? I would like to pin point where the elasticity in the system is coming from, while the cap is off.

Any feedback is greatly appreciated.

Thanks,

Ed