The thermostat controls the coolant temperature. When the coolant temperature is below the operating range,
coolant is bypassed back to the inlet of the water pump.
When the coolant temperature reaches the operating range, the thermostat opens, sealing off the bypass, forcing coolant to flow to the radiator.
Caution: Never operate the engine without a thermostat. Without a thermostat the path of least resistance
for the coolant is through the bypass to the pump inlet.
This will cause the engine to overheat.
An incorrect or malfunctioning thermostat can cause the engine to run too hot or too cold.
As described in the coolant discussion, jiggle pins vent air during filling of the coolant system.
After the engine is vented and filled, the jiggle pins act as check valves to block the flow of coolant through the
opening during engine operation.
NOTE: A missing jiggle pin can cause the engine to run cold.
With the jiggle pins sealing the openings, the flow to the radiator is controlled by the thermostat opening in response to the engine coolant temperature.
