Sierra 18-0398-9 Thermostat Gasket, Pack of 2, Replaces Mercruiser 27-33918 and OMC 385211

The Sierra 18-0398-9 thermostat gasket seals the thermostat housing on compatible marine engines, providing a leak-free seal between the housing and the engine block or manifold. Sold in a pack of two, it gives boat owners and technicians enough material on hand to complete a full thermostat service or to keep a spare for the next maintenance interval. The gasket is manufactured by Sierra to meet or exceed the quality of the original equipment part it replaces, making it a straightforward drop-in during a thermostat replacement, cooling system inspection, or general engine maintenance.

Because thermostat housings and gaskets are shared across several engine brands, the 18-0398-9 cross-references to a range of OEM part numbers from Mercruiser, OMC, Volvo Penta, GLM, and Mallory, so it can be ordered using whichever number appears on the old gasket or in the engine's parts manual. Its light weight and simple flat-gasket design make it easy to install with basic hand tools once the old thermostat and gasket are removed and the mating surfaces are cleaned.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-0398-9
• Product Type: Thermostat Gasket
• Package Quantity: Pack of 2
• Weight: 0.01 pounds
• UPC: 808282161569

Fitment

Fits engines that use a thermostat housing gasket cross-referenced to the Mercruiser, OMC, Volvo Penta, GLM, and Mallory part numbers listed below.

Replaces (OEM)

• GLM 35060
• Mallory 9-60009
• Mercruiser 27-33918
• Mercruiser 27-8M2021920
• OMC 385211
• OMC 312797
• Volvo Penta 835417

Frequently Asked Questions

What does the Sierra 18-0398-9 thermostat gasket cross-reference to? The Sierra 18-0398-9 thermostat gasket is interchangeable with GLM 35060, Mallory 9-60009, Mercruiser 27-33918, Mercruiser 27-8M2021920, OMC 385211, OMC 312797, and Volvo Penta 835417.

How many gaskets come with an order of 18-0398-9? This listing for the Sierra 18-0398-9 thermostat gasket is priced and sold as a pack of two gaskets.

Does the 18-0398-9 gasket meet original equipment quality? Yes, the Sierra 18-0398-9 thermostat gasket is manufactured to meet or exceed the quality of the original equipment part it replaces.

Will this gasket fit a Mercruiser engine thermostat housing? Yes, the Sierra 18-0398-9 gasket cross-references to Mercruiser part numbers 27-33918 and 27-8M2021920.

Is the 18-0398-9 gasket compatible with OMC engines? Yes, it cross-references to OMC part numbers 385211 and 312797.

Does the Sierra 18-0398-9 gasket work on Volvo Penta engines? Yes, the Sierra 18-0398-9 thermostat gasket cross-references to Volvo Penta part number 835417.

How much does the 18-0398-9 thermostat gasket weigh? The Sierra 18-0398-9 thermostat gasket weighs 0.01 pounds.

What UPC is used for the Sierra 18-0398-9 gasket? The Sierra 18-0398-9 thermostat gasket is identified by UPC 808282161569.

How do I confirm 18-0398-9 is the correct gasket for my engine? Match the part number stamped on your old thermostat gasket, or your engine's parts manual, against the cross-reference numbers for the Sierra 18-0398-9: GLM 35060, Mallory 9-60009, Mercruiser 27-33918, Mercruiser 27-8M2021920, OMC 385211, OMC 312797, or Volvo Penta 835417.

Is this a genuine Sierra part or a generic aftermarket copy? The 18-0398-9 is manufactured and sold under the Sierra brand, part number 18-0398-9, rather than an unbranded generic part.

What is included when I purchase the 18-0398-9 gasket? An order of Sierra 18-0398-9 includes two thermostat gaskets, sold as a pack.

Can the 18-0398-9 gasket be used with a Mallory or GLM thermostat housing? Yes, the Sierra 18-0398-9 thermostat gasket cross-references to GLM 35060 and Mallory 9-60009.