Sierra 18-1222 Thermostat Diaphragm Gasket, Johnson/Evinrude V4/V6 200/225 HP 1988-93, Replaces OMC 394408

The Sierra 18-1222 is a round thermostat diaphragm gasket for Johnson/Evinrude V4/V6 loop charge outboard engines. It seals the thermostat housing to the powerhead, maintaining proper cooling system pressure and preventing water leakage around the thermostat. This gasket is manufactured to meet or exceed original equipment specifications, making it a direct equivalent for the OEM diaphragm gasket used on covered Johnson/Evinrude V4/V6 outboards.

The gasket is a round, white component sized to match the OEM thermostat housing footprint on applicable Johnson/Evinrude V4/V6 powerheads. It is commonly replaced whenever the thermostat itself is serviced, since a worn or hardened gasket is a frequent source of coolant leaks and overheating on outboard motors. Fitment covers 200 HP and 225 HP Johnson/Evinrude outboards for the 1988-93 model years.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-1222
• Product Type: Thermostat Diaphragm Gasket
• Shape: Round
• Color: White
• Weight: 0.01 pounds
• UPC: 030999752376
• OEM Cross Reference: GLM 46130, 394408

Fitment

• Johnson/Evinrude V4/V6 loop charge outboard, 200 HP, 1988-93
• Johnson/Evinrude V4/V6 loop charge outboard, 225 HP, 1988-93

Replaces (OEM)

• GLM 46130
• 394408

Frequently Asked Questions

What engines does the Sierra 18-1222 thermostat diaphragm gasket fit? The Sierra 18-1222 fits Johnson/Evinrude V4/V6 loop charge outboard engines rated at 200 HP and 225 HP for the 1988-93 model years.

Is the Sierra 18-1222 a direct OEM equivalent? Yes, the 18-1222 is interchangeable with GLM 46130 and OEM number 394408, and it meets or exceeds the quality of the original equipment part it replaces.

What OEM part numbers does 18-1222 cross-reference to? 18-1222 crosses to GLM 46130 and OMC/Evinrude/Johnson 394408.

What shape and color is this gasket? The 18-1222 thermostat diaphragm gasket is round and white.

How much does the Sierra 18-1222 gasket weigh? It weighs 0.01 pounds.

Should the thermostat diaphragm gasket be replaced when installing a new thermostat? Yes, replacing the 18-1222 gasket whenever the thermostat is serviced helps prevent coolant leaks caused by a worn or hardened seal at the thermostat housing.

What is included with the Sierra 18-1222? The 18-1222 is sold as a single thermostat diaphragm gasket.

Is the Sierra 18-1222 genuine Sierra or aftermarket? It is a genuine Sierra-branded part manufactured to meet or exceed the OEM specification for part 394408, not a generic aftermarket substitute.

What is the UPC for the Sierra 18-1222 gasket? The UPC is 030999752376.

Does the 18-1222 gasket work on 235 HP or 200 HP 1977-83 Johnson/Evinrude engines? No, the 18-1222 is specified for 200 HP and 225 HP Johnson/Evinrude V4/V6 outboards built 1988-93; earlier 200 HP (1977-83) and 235 HP applications use a different Sierra thermostat gasket.