I dont have a diagram, but I would think that the coolant would simply not exit the back of cylinder head, and continue its normal way around the block and head until it exits back out the front, through the upper hose to the radiator. The way I understand it, cool water from radiator goes into the water pump through the lower radiator hose, from there into the engine block, then through the cylinder head and back out through the thermostat and upper radiator hose. When the engine is cold, the thermostat shuts so that water only flows around the block and head for quick warm up.
Pretty sure thats how it works.

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Streetside: 1987 Mercedes 300E Petrol Blue/Green
2014 Ford Mustang Grabber Blue
1999 Ford Ranger Green

Dockside: 1968 Eltro 17
1985 Silverton 34C