Overheating 360 new engine

I went through a similar issue. I did not read through all the comments but there were a few concerns that come to mind, and one of them is not air flow. I sealed everything, running a 3000 cfm fan, i can touch the radiator fins and they are not burning at all when my engine was at 205-210. The things I mention can al be done for free also.

First thing is make sure that the March Performance is turning the water pump the same direction as stock as you may be pulling the fluid at the pump rather than pushing it. It will still flow coolant, but not well.

Second, how is your heater core hooked up? Do you have it looped, or straight to the heater core and straight back? Either way, the coolant takes the path of least resistance. Make sure there is an inline shut off valve of some sort. Coolant is coming out of the head (hottest point) and if looped to the water pump, it is just flowing that hottest water back into the water pump to push through the block again. This compounds the heating and gives you a giant hot spot where your temp sensor is.

A way to test this theory is to put a set of vice grips on the hose going out of the block that is supposed to go to the heater core. This will stop that hot water from going back into the water pump and force it through the thermostat and radiator.