Lower Unit Drain Gasket – Fits Yamaha 4-Stroke Outboards (Replaces Yamaha 90430-08003-00, 90430-08020-00, Mercury 27-81987)
Lower Unit Drain Gasket – Fits Yamaha 4-Stroke Outboards (Replaces Yamaha 90430-08003-00, 90430-08020-00, Mercury 27-81987) is backordered and will ship as soon as it is back in stock.
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Worry-free returns
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Delivery and Shipping
Delivery and Shipping
Free standard shipping on all orders under 1 KG
Lower Unit Drain Gasket – Fits Yamaha 4-Stroke Outboards (Replaces ...
Product Details
This fiber/composite Yamaha Outboard Lower Unit Drain Gasket creates a secure, leak-free seal for the lower unit drain and vent plugs. It is designed for a wide range of Yamaha 4-Stroke Outboard Motors, from 2.5 HP to 350 HP, manufactured from 1998 to the present.
It serves as a direct replacement for Yamaha part numbers 90430-08003-00 and 90430-08020-00, as well as aftermarket equivalents like Sierra 18-0826 and Mercury 27-81987.
- Installs with basic hand tools.
- Functions as a compression crush washer for a tight seal.
- This is the newer black composite style that supersedes the earlier reddish-orange version.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number | Notes |
|---|---|---|
| Yamaha | 90430-08003-00 | Current OEM part. Supersedes 90430-08020-00. |
| Yamaha | 90430-08020-00 | Earlier reddish-orange part, superseded by 90430-08003-00. |
| Sierra | 18-0826 | Direct aftermarket cross-reference. |
| Mercury | 27-81987 | Interchangeable aftermarket part. |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
This gasket fits nearly all Yamaha 4-stroke outboards from 2.5 to 350 HP manufactured between 1998 and today.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Yamaha | F2.5 | 2.5 | 4-Stroke | 2003–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F4 | 4 | 4-Stroke | 1999–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F6 | 6 | 4-Stroke | 1999–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F8 | 8 | 4-Stroke | 2000–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F9.9 | 9.9 | 4-Stroke | 2000–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F15 | 15 | 4-Stroke | 1998–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F20 | 20 | 4-Stroke | 1998–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F25 | 25 | 4-Stroke | 1998–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F30 | 30 | 4-Stroke | 1998–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F40 | 40 | 4-Stroke | 1999–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F50 | 50 | 4-Stroke | 1999–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F60 | 60 | 4-Stroke | 2002–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F70 | 70 | 4-Stroke | 2010–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F75 | 75 | 4-Stroke | 1998–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F80 | 80 | 4-Stroke | 2000–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F90 | 90 | 4-Stroke | 2000–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F100 | 100 | 4-Stroke | 2000–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F115 | 115 | 4-Stroke | 2000–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F150 | 150 | 4-Stroke | 2004–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F175 | 175 | 4-Stroke | 2004–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F200 | 200 | 4-Stroke | 2004–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F225 | 225 | 4-Stroke | 2004–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F250 | 250 | 4-Stroke | 2004–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F300 | 300 | 4-Stroke | 2004–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
| Yamaha | F350 | 350 | 4-Stroke | 2008–Present | 90430-08003-00 | Supersedes 90430-08020-00 |
Technical Specs
- Product Type
- Lower Unit Drain Gasket
- Installation
- Manual (hand tools)
- Connection
- Compression washer
- Housing Material
- Fiber/Composite
- Housing Color
- Black (newer style); earlier versions were reddish-orange
- Dimensions
- Approx. 19 mm OD
- Weight
- <5g
- Fitting Type
- Crush washer
- Thread Size
- Compatible with M8 drain plugs
- Other Attributes
- Supersedes earlier reddish-orange gasket (90430-08020-00)
What’s in the Box
- 1 x Gasket (Replaces 90430-08003-00)
Note: This gasket is used on both the vent and drain plug. For a complete lower unit oil change, order quantity two.
Installation Notes
- Position a drain pan under the lower unit.
- Remove both the lower drain plug and the upper vent plug screws.
- Allow the gear oil to drain completely. Inspect the old oil for a milky appearance (water) or metal filings.
- Clean the plug sealing surfaces on the gearcase.
- Remove and discard the old gaskets from both plugs. Never reuse them.
- Install a new gasket on each plug.
- Inject the recommended gear lube into the bottom drain hole until fluid flows from the upper vent hole.
- Install the upper vent plug with its new gasket first. Tighten securely.
- Quickly remove the lube filler tube and install the lower drain plug.
- Tighten the drain plug to the manufacturer's specified torque. Do not overtighten.
- Wipe the area clean and check for any leaks after a few minutes.
Troubleshooting & FAQ
How do I know if this gasket is overtightened?
Over-tightening can crush the gasket and cause a leak. Always tighten plugs to the manufacturer's specified torque using a torque wrench. If one is not available, tighten until snug, then turn an additional 1/4 turn. The gasket should feel compressed but not distorted.
The new black gasket feels harder than my old red one. Is this correct?
Yes. The current Yamaha OEM part (90430-08003-00) is a black, harder composite material that supersedes the older, reddish-orange gasket (90430-08020-00). While some users note a difference in feel, this is the correct updated part for the specified models.
How often should I replace these gaskets?
It is critical to use a new gasket every time you change your lower unit gear oil. Reusing old, crushed gaskets is a primary cause of leaks and potential water intrusion, which can lead to catastrophic gearcase failure.
What are the signs of a failed drain plug gasket?
The most common sign is a slow drip of gear oil from the drain or vent plug. Another key indicator is milky or creamy-looking oil during a fluid change, which signals water has entered the lower unit through a failed seal.
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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