Gasket, Water Outlet Housing – Fits Mercury & MerCruiser 3.0L (Replaces 27-33918, 8M2021920)
Gasket, Water Outlet Housing – Fits Mercury & MerCruiser 3.0L (Replaces 27-33918, 8M2021920) is backordered and will ship as soon as it is back in stock.
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Delivery and Shipping
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Gasket, Water Outlet Housing – Fits Mercury & MerCruiser 3.0L (...
Product Details
This Gasket, Water Outlet Housing creates a secure seal between the water outlet housing and the distribution block. It is designed specifically for Mercury Marine and MerCruiser 3.0L GM 181 I/L4 inline 4-cylinder engines manufactured between 1998 and 2020.
This part is a direct replacement for Mercury OEM part numbers 27-33918 and 8M2021920. Note that the newer part 8M2021920 is a functional replacement and may differ in appearance from the original.
- Installation Location: Between water outlet housing and distribution block.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number | Superseded By |
|---|---|---|
| Mercury | 27-33918 | 8M2021920 |
Engine & Model Compatibility
Confirm your engine model and year in the table below.
Fits a wide range of MerCruiser sterndrive models, primarily within the 3.0L engine family, but also includes legacy 110, 120, 140, 150, and 160 models.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| MerCruiser | 3.0L GM 181 I/L4 | 135 | 4-Stroke | 1998–2020 | 27-33918/8M2021920 | 0L010042 THRU 0L096999, 0L097000 THRU 0W301999, 0W302000 THRU 1A0019999, 1A002000 THRU 1A020543, 1A020544 & Up |
| MerCruiser | 3.0L MPI EC | 135 | 4-Stroke | 2006–2020 | 27-33918/8M2021920 | 1A072812 & Up |
| MerCruiser | 3.0LX GM 181 I/L4 | 135 | 4-Stroke | 1996–1997 | 27-33918/8M2021920 | 0F604000 THRU 0K999999 |
| MerCruiser | 3.0L TKS Plus | 135 | 4-Stroke | 2005–2020 | 27-33918/8M2021920 | 1G404114 & Up |
| MerCruiser | 120 GM 153 I/L4 | 120 | 4-Stroke | 1964–1972 | 27-33918/8M2021920 | 1666601 THRU 3377340 |
| MerCruiser | 110 GM 153 I/L4 | 110 | 4-Stroke | 1963–1966 | 27-33918/8M2021920 | 1537370 THRU 2044033 |
| MerCruiser | 140 GM 194 I/L6 | 140 | 4-Stroke | 1963 | 27-33918/8M2021920 | 1538930 THRU 1725960 |
| MerCruiser | 150 GM 230 I/L6 | 150 | 4-Stroke | 1964–1966 | 27-33918/8M2021920 | 1666495 THRU 2048046 |
| MerCruiser | 160 GM 250 I/L6 | 160 | 4-Stroke | 1967–1969 | 27-33918/8M2021920 | 2048022 THRU 2770031 |
Technical Specs
- Product Type
- Gasket
- Installation
- Between water outlet housing and distribution block
- Dimensions
- 4.0" H x 5.13" W x 1.13" L
- OEM Part Number
- 27-33918 (superseded by 8M2021920)
What’s in the Box
- 1 x Gasket, Water Outlet Housing (27-33918/8M2021920)
Installation Notes
- Disconnect the battery and drain the cooling system to a level below the thermostat housing.
- Loosen and remove the mounting bolts securing the water outlet housing to the engine's distribution block.
- Gently remove the housing. You may need to tap it lightly to break the old seal.
- Carefully scrape away all remnants of the old gasket from both the housing and the block mating surfaces. Ensure both surfaces are clean, dry, and free of debris.
- Position the new gasket correctly over the dowel pins or alignment holes on the distribution block.
- Reinstall the water outlet housing, ensuring it sits flush against the new gasket.
- Tighten the mounting bolts in a crisscross pattern to the manufacturer's specified torque to ensure even pressure.
- Reconnect the battery, refill the engine with coolant, and run the engine while checking for any leaks around the housing.
Troubleshooting & FAQ
How do I confirm this gasket fits my engine?
Check your engine's serial number against the ranges listed in the Engine & Model Compatibility table. The most reliable method is to verify the OEM part number (27-33918 or 8M2021920) is what is specified for your specific engine model and serial number in your service manual.
What are the signs of a failing water outlet housing gasket?
Common symptoms include visible coolant leaks (often leaving a white or colored crusty residue) around the gasket area, unexplained coolant loss, and engine overheating caused by air entering the cooling system or coolant escaping.
The new gasket (8M2021920) looks different from my original part (27-33918). Is it correct?
Yes. Part number 27-33918 was superseded by 8M2021920. The new part is a functional replacement certified by the manufacturer and may have a different appearance or be made from updated materials, but it will fit and perform correctly.
How often should this gasket be replaced?
There is no fixed replacement interval. This gasket should be replaced any time the water outlet housing is removed for service (such as for a thermostat replacement) or if it shows any signs of leaking or degradation.
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 and specifications against 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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