Mercury MerCruiser Thermostat Housing Assembly 864398T1

Mercury MerCruiser Thermostat Housing Assembly 864398T1 is a genuine Mercury OEM cooling system component designed for select MerCruiser gasoline engines. It provides the housing and coolant routing required for proper thermostat operation and engine temperature regulation.

Compatible with select MerCruiser applications including:

• 4.3L Carb and MPI
• 5.0L MPI
• 5.7L MPI
• 350 MAG and 377 MAG
• 6.2L MPI / MX 6.2L
• Select sterndrive and inboard configurations
• Select closed-cooling configurations

The thermostat housing is part of the engine cooling system and directs coolant flow through the thermostat and associated cooling passages. Replacing a corroded, damaged, or leaking housing helps maintain proper coolant circulation and engine operating temperature.

Important: Some applications use different thermostat housings depending on whether the engine has mechanical or Digital Throttle & Shift controls. For example, certain 377 MAG applications use 864398T1 for mechanical throttle and shift, while DTS configurations use a different housing.

To Confirm Compatibility: Contact our team with your engine serial number at (727) 596-5929 before ordering.