Your engine is equipped with (2) Thermostats. When the Engine is cold and both the primary and secondary thermostats are closed. The coolant will circulate through the engine, heater system, and the bypass. The cooling system has no flow through the radiator. As the engine warms up, the primary thermostat will start to open at 179 °F. Coolant will start to flow through the radiator oil cooler and transmission cooler. Coolant will flow through the transmission oil cooler only when the primary thermostat is fully open. The primary thermostat will fully open at 203 °F. The secondary thermostat will start to open at 203 °F. This will increase the coolant flow through the cylinder block and cylinder head and the radiator. The secondary thermostat will fully open at 230 °F. PRIMARY THERMOSTAT ; Partially drain THE cooling system. Remove THE air filter housing. Disconnect the coolant hose from the inlet housing (small diameter hose below the Radiatior Hose). Remove inlet housing bolts. Remove the thermostat assembly, and clean the sealing surfaces. SECONDARY THERMOSTAT; Remove the air filter housing. Disconnect coolant hoses from rear of the coolant adapter. Remove the radiator hose. Remove the radiator hose from the front of the coolant adapter. 6. Remove the coolant adapter mounting bolts. Carefully slide the coolant adapter off the water pump inlet tube and remove the coolant adapter and the secondary thermostat.