DTC P0128 Coolant Thermostat (Coolant Temp. Below Thermostat Regulating Temp.): General Description

The Thermostat is a mechanical (thermal) device located in an engine coolant passage that allows passage of coolant into the radiator once the coolant has reached a manufacturer specified temperature called the Regulating Temperature. It has a metallic frame with a spring-loaded, centrally mounted, wax filled cylinder/piston assembly that expands and contracts with changes in temperature, thereby controlling the passage of coolant into the radiator.