Overheating 360 new engine

I get a kick outta how many folks forget about all the parasitic power loss thru friction, belts, bearings, brushes, magnetism, drag, etc, etc. that a water pump mounted fan doesn't have.
Clutch fans don't spin over 4k ish, and sorta freewheel when hot.
Each has it's advantages, mounting being a deciding factor .
Electric fans do take power, it's not free !
My racecars have significant rpm loss when the fans kick on !
jmo

Nobody said electric fans were "free". But the difference in running a 60 amp alternator and a 100 amp or even a 200 amp alternator isn't that much. There's very little difference at all unless the fans are actually running and requiring the higher amperage, the difference in friction from the belts, bearings, brushes etc is almost nothing unless you're pulling the higher draw. You have to run an alternator regardless, so you're not going to get rid of friction from the belt, bearings, etc.

And it depends on the type of clutch fan. Simple hydrostatic clutches never free wheel. Some of the better thermostatic clutches can do better, but most of them aren't 100% free wheeling either. And that's assuming a clutch fan is being used, seems like most of the argument in this thread is guys running straight mechanical fans that will be 100% all the time.

There are advantages and disadvantages to both, the bottom line is that in either case you have to set the system up correctly. Both mechanical and electric fans can be inadequate if set up improperly.

A couple things come to mind and this is my ante or $.02...at first it sounds like a restriction int he water jackets in the block or heads, but I have to be honest ive never enncountered this no more than an extremely sludged radiator or a bad thermostat...second, That belt drive, is the water pump spinning the right way? are you sure? really sure...? I have seen bad water pump impellers that act like you describe OP. I forget what car had plastic impellers and they would grenade causing an overheat, i think it was Ford...second Ive seen completely rusted out impellers act this way, but I would assume yours is a new water pump so it could be spinning backwards. Good luck...

This water pump spinning backwards thing again.

Guys, you know that in order to run a Magnum water pump with a reverse rotation you'd need the magnum timing cover too right? March does not specify a reverse rotation water pump with their LA kits, and it's a big change to make. In fact, you can go right to March's website and download the instructions for their kit. It has a nice little diagram in it, which shows the belt routing and the normal LA water pump rotation is maintained. In the pictures the OP posted you can clearly see the belt on top of the water pump pulley.
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Or go an download the instructions yourself and take a look...
Chrysler 318/340/360 : Style Track : Includes alternator and air conditioning with optional power steering