D 350 Pickup L6-359 5.9L DSL (1989)
As previously discussed, jiggle pins are fitted to openings in the thermostat flange, to vent air from the cooling system during fill, and to act as check
valves to block the flow of coolant through the openings during engine operation.
NOTE: A missing jiggle pin can cause the engine to run cold.
With the jiggle pins sealed, the flow to the radiator is controlled by the thermostat responding to the engine coolant temperature.
