Sierra Retainer Gasket 18-1221-9, 2-Pack, Fits Johnson/Evinrude 200 HP and 225 HP (1988-93)

The Sierra Retainer Gasket 18-1221-9 is a two-pack replacement gasket used with the thermostat retainer on select Johnson/Evinrude (OMC/BRP) outboard powerheads. This gasket seals the retainer housing that holds the thermostat in place within the cooling system, helping maintain proper sealing pressure and preventing coolant leakage around the retainer during operation. Sold as a set of two, it gives an installer a spare on hand for a follow-up service or a second engine, which is useful since gaskets should be replaced any time the retainer is removed rather than reused. This part is specifically called out in Sierra's application charts for Johnson/Evinrude 200 HP outboards built 1988-93 and 225 HP outboards built 1988-93, distinguishing it from the separate part number used on earlier 185 HP, 200 HP (1977-83), and 235 HP models in the same engine family. Confirming the exact HP and year of the outboard before ordering ensures the correct retainer gasket is installed, since Sierra lists a different part number for those other model years. As with any gasket, proper surface prep and correct torque on the retainer hardware during reassembly are important to achieve a good seal.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-1221-9
• Package Quantity: 2 gaskets
• Weight: 0.03 pounds
• Category: Thermostat Retainer Gasket
• UPC: 808282162368
• Fitment: Johnson/Evinrude (OMC/BRP) 200 HP (1988-93), 225 HP (1988-93)

Fitment

• Johnson/Evinrude (OMC/BRP) 200 HP, 1988-93
• Johnson/Evinrude (OMC/BRP) 225 HP, 1988-93

Replaces (OEM)

• No OEM cross-reference numbers are listed for this part.

Frequently Asked Questions

What is the Sierra 18-1221-9 retainer gasket used for? It seals the thermostat retainer on the powerhead of compatible Johnson/Evinrude (OMC/BRP) outboards, part 18-1221-9, helping the retainer housing hold pressure and keep coolant from leaking around the thermostat area.

How many gaskets come in the Sierra 18-1221-9 package? Two retainer gaskets are included in each 18-1221-9 package, giving you a spare for a future service.

Which outboards does part 18-1221-9 fit? Sierra's application chart lists 18-1221-9 for Johnson/Evinrude (OMC/BRP) 200 HP outboards built 1988-93 and 225 HP outboards built 1988-93.

Does 18-1221-9 fit earlier 200 HP Johnson/Evinrude outboards from the 1970s and 80s? No. Sierra's chart shows a different retainer gasket part number for 200 HP models built 1977-83, so 18-1221-9 is specific to the 1988-93 200 HP and 225 HP applications.

Is 18-1221-9 the same gasket used on 185 HP or 235 HP Johnson/Evinrude models? No. Those horsepower ratings (185 HP 1984-85 and 235 HP 1978-85) use a different Sierra part number in the same application chart, not 18-1221-9.

How much does the Sierra 18-1221-9 gasket set weigh? The 18-1221-9 two-pack weighs 0.03 pounds.

Should the retainer gasket be reused after removing the thermostat retainer? No, a fresh gasket like the Sierra 18-1221-9 should be installed any time the thermostat retainer is removed, since a used gasket may not reseal properly.

Is the Sierra 18-1221-9 gasket genuine OEM or an aftermarket replacement? The 18-1221-9 is a Sierra-branded replacement gasket manufactured to fit the specified Johnson/Evinrude outboard applications; no OEM cross-reference number is listed for it in Sierra's catalog.

What is included when I order part 18-1221-9? Ordering 18-1221-9 gets you a package of two thermostat retainer gaskets; no other hardware or thermostat is included.

What UPC is associated with the Sierra 18-1221-9 gasket 2-pack? The UPC for the 18-1221-9 two-pack is 808282162368.