A thermostat assembly for use with an engine cooling system includes a thermostat, a frame, a bypass valve and an integrated filter. The frame supports the thermostat and is positioned upstream of a thermostatic valve. The frame also defines a primary coolant passage. The bypass valve is positioned on the frame and selectively defines a bypass coolant passage. The filter is positioned on the frame upstream of the thermostat and is configured to filter coolant flowing through the primary coolant passage to the thermostat. The bypass valve moves between a normally closed position and an open position where coolant is free to pass through the bypass coolant passage and to the thermostat. The bypass valve moves to the open position upon being subjected to a predetermined pressure caused by a reduction in a coolant flow rate through the filter so as to provide for coolant flow to bypass the filter.