MY STOCK MERC. CENTERISE MANIFOLD COOLING PATH IS AS FOLLOWS.RAW WATER TO OIL COOLER TO HEAT EXCHANGER TO RISERS.CLOSED COOLING GOES FROM WATER PUMP THROUGH ENGINE,OUT THERMOSTAT HOUSING TO MANIFOLD LOWER FITING OUT MANIFOLD UPPER FITTING BACK TO HEAT EXCHANGER THEN TO WATER PUMP.WHEN THE THERMOSTAT IS CLOSED AND THE BLOCK WATER IS CICULATING OUT THE BYPASS HOSE BACK TO THE WATER PUMP THER IS NO CICULATION THROUGH THE MANIFOLDS.THERE WAS NO PROBLEM WITH THIS SETUP.WITH MY WINTER REBUILD I BOUGHT A SET OF STAINLESS MARINE MANIFOLDS.I TALKED TO STAINLESS MARINE TECH DEPT. AS I WAS CONCERNED WITH OVERHEATING THE ALUMINUM MANIFOLDS IN WARM UP(CLOSED THEMOSTAT)MODE.HE TOLD ME THERE WOULD BE NO PROBLEM.I STARTED MY NICE NEW SHINNY MOTOR TODAY AND IT TOOK ABOUT 2 MINUTES AND THE WATER IN MANIFOLDS WAS BOILING OVER AND MAKING THE WATER IN HEAT EXCHANGER BLOW OVER THE CAP.SO MUCH FOR THE CLEAN MOTOR AND BOAT.ANY IDEAS ON HOW TO PLUMB THIS OR SHOULD I JUST PLUMB THE RAW WATER INTO THE MANIFOLDS

I have closed cooling on my motor. The manifolds are cooled by raw water. The raw water flows from the pump to the oil cooler to the heat exchanger then out the manifolds. Works great, never a problem. Only draw back is obviously salt water in the manifolds. At least the motor stays clean.