I believe you're reading the back pressure between the cooler and raw water pump, not what the actual engine is seeing.

says it is closed cooling so the block is not seeing this pressure, only the raw side and right after the pump. as pressure is only the resistance of the incoming water and the outgoing water you have too much blockage somewhere. I would see if you can take pressure at the exhaust manifold and if way lower then after the oil cooler, if still way high the heat exchanger is not flowing enough.