[Bob Bidonde]

The water pump is in the wrong place in the cooling system. The pump should always have an adequate coolant supply, pressure heads at the inlet and outlet, and would have this if it were in the lower radiator hose. The supply line to the pump would need to be larger than the outlet line (perhaps 50% larger).

The attempt by Ford to steer flow with a diverter at the water inlet in the block is not a sound design. The diverter is evidence that Ford became aware of the flow issue at the back of the engine. Again, this shows a lack of understanding fluid mechanics. The diverter has a local effect, and be of some benefit to Cylinder 3.

Regardless of what the surface temperatures are, the evidence (gasket burnout; cleaner running plugs) is clear that Cylinders 3 & 4 run hotter internally. In my opinion, surface temperatures are subject to higher heat transfer rates because of the liquid (conduction) and air cooling (radiation & convection) effects. Thus the surface temperatures are not an accurate indication of what occurs in the head and block at Cylinders 3 & 4.

I have a suspicion that micro-boiling may be occurring in the head at Cylinder 4.

A better design, but not the best idea is to move the water inlet: