Engine Coolant Flow Control Valve {If Equipped}

The engine water outlet includes a engine coolant flow control valve, which opens at around 4, 000 RPM. All coolant is circulated through the heater core when the RPM is below 4, 000 while the engine thermostat is fully closed during engine warm up. The engine coolant flow control valve opens at around 4, 000 RPM and above, which stops increase of flow rate to the heater core and forces some portion of coolant through a heater bypass loop in order to protect the heater core from excessive coolant pressure. In rare cases, the engine coolant flow control valve may be stuck open, causing a lack of cabin heat.