Upper hose goes to t-stat, which will close (if not already) when cold water contacts it.

I've had good luck getting the right front as high as practicable, and feeding in the water as required. Kick on the heater so you get circulation to purge the air in it as well.

Jim

__________________
14 E250 BlueTEC black. 45k miles
95 E320 Cabriolet Emerald green 66k miles
94 E320 Cabriolet Emerald green 152k miles
85 300TD 4 spd man, euro bumpers and lights, 15" Pentas dark blue 274k miles