Heater Housing, Thermostat Support and Water Header Cover (8-09) Section 8 - Cooling System - Group 08 M11 Page 8-40 Install a new o-ring and the cover plate. Heater Housing, Thermostat Support and Water Header Cover - Cleaning and Inspection (8-09) Cleaning Remove the gasket material from the engine heater hous- ing surface (1). Remove the gasket material from the thermostat support surfaces (2, 3 and 4). Remove the gasket material from the water header cover surfaces (5, 6 and 7).