Thermostat Cover Gasket – Fits MerCruiser / Johnson / Evinrude 2-Cylinder Engines (Replaces 318917, REC318917)
Thermostat Cover Gasket – Fits MerCruiser / Johnson / Evinrude 2-Cylinder Engines (Replaces 318917, REC318917) is backordered and will ship as soon as it is back in stock.
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Worry-free returns
You may return most new, unopened items within 7 days of delivery for a full refund. We'll also pay the return shipping costs if the return is a result of our error (you received an incorrect or defective item, etc.).
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Delivery and Shipping
Delivery and Shipping
Free standard shipping on all orders under 1 KG
Thermostat Cover Gasket – Fits MerCruiser / Johnson / Evinrude 2-Cy...
Product Details
This Thermostat Cover Gasket – Fits MerCruiser / Johnson / Evinrude 2-Cylinder Engines provides a reliable seal between the thermostat housing and the engine block. It is designed specifically for 2-cylinder crossflow engines, including certain MerCruiser models and various Evinrude/Johnson 9.9-15 HP outboards.
It serves as a direct interchange for Evinrude/Johnson part numbers 318917 and 777933, as well as Sierra 18-0397 and GLM 34890.
- Installs between the thermostat housing and engine block to prevent coolant leaks.
- Constructed from high-quality compressed fiber gasket material for a durable, long-lasting seal.
- Engineered specifically for use on 2-cylinder crossflow marine engines.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket brands.
| Brand | Part Number |
|---|---|
| Evinrude/Johnson | 318917 |
| Evinrude/Johnson | 777933 |
| Sierra | 18-0397 |
| GLM | 34890 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
For MerCruiser, this gasket is compatible with 2-cylinder crossflow models.
| Brand | Model | OEM Part No. | Notes |
|---|---|---|---|
| MerCruiser | 2-Cylinder Crossflow | REC318917 | High-quality sealing gasket |
For Evinrude/Johnson, this gasket fits various 2-stroke, 2-cylinder crossflow outboards, typically in the 9.9-15 HP range.
| Brand | Model | Rated HP | Stroke | OEM Part No. | Notes |
|---|---|---|---|---|---|
| Evinrude/Johnson | 2-Cylinder Crossflow | 9.9-15 | 2-Stroke | 318917/777933 | Water cover gasket |
Technical Specs
- Product Type
- Thermostat Cover Gasket
- Installation
- Between thermostat housing and engine block
- Housing Material
- Compressed fiber gasket material
- Dimensions
- 7.5 cm × 6.0 cm × 1.13 cm (2.95" × 2.36" × 0.44")
- Weight
- 0.02 kg (0.04 lb)
- Other Technical Attributes
- Used on 2-cylinder crossflow engines
What’s in the Box
- 1 x Thermostat Cover Gasket (318917/REC318917)
Installation Notes
- Ensure the engine is completely cool and disconnect the battery for safety.
- Drain a sufficient amount of coolant to bring the level below the thermostat housing.
- Carefully unbolt and remove the thermostat cover. Note the orientation of the parts.
- Remove the old gasket and meticulously clean both the engine block and thermostat cover mating surfaces. All traces of old material must be removed for a proper seal.
- Position the new gasket correctly, aligning it with the bolt holes.
- Reinstall the thermostat cover and tighten the bolts to the manufacturer's recommended torque, usually in a crisscross pattern to ensure even pressure.
- Refill the cooling system with the appropriate coolant, reconnect the battery, and run the engine to check for any leaks around the housing.
Troubleshooting & FAQ
How do I confirm this gasket fits my specific engine model?
This gasket is designed for MerCruiser and Evinrude/Johnson 2-cylinder crossflow engines. The most reliable method is to cross-reference your existing part number with the ones listed in our Part Number Matrix (Evinrude/Johnson 318917/777933, Sierra 18-0397, etc.). Always visually compare your old part to our product images.
What are common signs of a failed thermostat cover gasket?
The most obvious sign is a visible coolant leak around the thermostat housing. Other symptoms can include the engine overheating due to coolant loss or unexplained drops in the coolant level.
Can I reuse my old gasket after removing the cover?
No. Gaskets are single-use components designed to compress and create a seal. Once the seal is broken, the gasket should always be replaced to prevent future leaks.
When should this gasket be replaced?
It's best practice to replace the thermostat cover gasket whenever you service or replace the thermostat itself. It should also be replaced immediately if you notice any signs of leaking or damage.
What makes this gasket different from the original OEM part?
Our aftermarket gasket is engineered to meet or exceed original equipment manufacturer (OEM) specifications for fit, form, and function. It is made from a comparable high-quality compressed fiber material to ensure a reliable and durable seal under marine conditions.
Is any sealant required during installation?
Generally, this type of gasket is designed to be installed dry. However, always consult your engine's service manual. If sealant is recommended, use only a thin, even layer of a type specified for marine cooling systems.
OEM vs. Aftermarket?
This listing is an aftermarket replacement (not OEM). Built to OEM-level specifications with comparable materials. Manufactured in an ISO 9002 facility, batch-inspected for consistency.
Shipping speed & cost?
We ship worldwide quickly—typical transit 5–15 days. Standard shipping is free; expedited options appear at checkout where available.
Warranty & returns?
Covered by a 1-year warranty against manufacturing defects under normal use. If issues arise, contact support with your order details. Returns are accepted within our standard window (unused & in original condition). See our policy page or reach out for instructions.
Safety & Important Info
- Verify images/specifications vs your original part. If anything differs—even if your model appears compatible—do not purchase.
- This is an aftermarket replacement, not an OEM component.
- Professional installation is recommended for safety and performance.
About Sea Sierra
- Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and tested for real-world conditions.
- Fast Global Fulfillment — Free standard delivery to most regions in 5–15 days.
- Manufacturer-Direct Value — Fair pricing without compromising on materials or QC.
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