I have always put a venting system in the top of the head for the sole reason of getting all the air out of the engines cooling system.
That is exactly what the jiggle pin does. If one wanted to they could remove the little hose (or the valve) and wait for coolant to come out while filling. However, doing it by the FSM works very well.
5.9L Diesel Engine Only; The
diesel engine is equipped with a one-way check valve
(jiggle pin). The check valve is used as a servicing
feature and will vent air when the system is being
filled. Water pressure (or flow) will hold the valve
closed. Due to the use of this valve, the engine
must not be operating when refilling the cooling
system. Refer to Thermostat Operation—5.9L
Diesel Engine in the Thermostat section of this group
for more information.
(4) Fill coolant reserve/overflow tank to the FULL
(5) Start and operate engine until thermostat
opens. Upper radiator hose should be warm to touch.
(6) If necessary, add 50/50 water and antifreeze
mixture to the coolant reserve/overflow tank to maintain
coolant level. This level should be between the
ADD and FULL marks. The level in the reserve/overflow
tank may drop below the ADD mark after three
or four warm-up and cool-down cycles