[1966geeto]

I finished the build on my 72 455 GP can't seem to figure this one out everything is new and it gets hot on start up only first 5 minutes run time then will run cool without any issues .Start up will go to 240 to 260 can hear the coolant popping gets that hot hoses get rock hard then everything goes to normal never gets over 200 while driving or idling .
Block bored 30 over.
Heads completely done 6x4
New heavy duty fan clutch
New radiator core with oversize core
Second thermostat 185 degrees
Water pump original done by Kellog with separator plate and spacing
every hose changed
coolant and purified water correct mixture
Long branch manifolds with 3 inch exhaust
As soon as the t stat opens all the way my temp drops and everything is normal makes no sense great flow through radiator getting frustrated and hate to even ask but at a dead end !