Gearcase Drain Plug – Fits Mercury/MerCruiser Marine Engines (Replaces 10-79953Q04, 10-79953A2)
Gearcase Drain Plug – Fits Mercury/MerCruiser Marine Engines (Replaces 10-79953Q04, 10-79953A2) is backordered and will ship as soon as it is back in stock.
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Worry-free returns
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.).
You should expect to receive your refund within four weeks of giving your package to the return shipper, however, in many cases you will receive a refund more quickly. This time period includes the transit time for us to receive your return from the shipper (5 to 10 business days), the time it takes us to process your return once we receive it (3 to 5 business days), and the time it takes your bank to process our refund request (5 to 10 business days).
If you need to return an item, simply login to your account, view the order using the "Complete Orders" link under the My Account menu and click the Return Item(s) button. We'll notify you via e-mail of your refund once we've received and processed the returned item.
Delivery and Shipping
Delivery and Shipping
Free standard shipping on all orders under 1 KG
Gearcase Drain Plug – Fits Mercury/MerCruiser Marine Engines (Repla...
Product Details
This Gearcase Drain Plug – Fits Mercury/MerCruiser Marine Engines is a crucial component for draining and refilling gearcase lubricant in the lower unit. It is designed for a wide range of Mercury outboard engines, including 30-125 HP EFI models, and various MerCruiser sterndrive units.
This part serves as a direct replacement for Mercury part numbers 10-79953Q04, 79953Q04, 10-79953A2, 10-79953Q2, as well as aftermarket equivalents like Sierra 18-2244 and Mallory 9-72650.
- Includes a new sealing washer/gasket for a leak-free fit.
- Features a standard 3/8-16 threaded design for simple installation.
- Non-magnetic construction prevents metallic debris from interfering with readings.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Mercury | 10-79953Q04 |
| Mercury | 79953Q04 |
| Mercury | 10-79953A2 |
| Mercury | 10-79953Q2 |
| Sierra | 18-2244 |
| Mallory | 9-72650 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
For Mercury models, this plug fits a variety of 4-Stroke EFI engines. For MerCruiser, it is used in sterndrive applications.
| Brand | Model | Rated HP | Stroke | OEM Part No. | Notes |
|---|---|---|---|---|---|
| Mercury | 3 Cyl EFI | 30, 40 | 4-Stroke | 10-79953Q04, 10-79953A2 | |
| Mercury | 3 Cyl EFI | 75, 80, 90, 115, 125 | 4-Stroke | 10-79953Q04, 10-79953A2 | |
| Mercury | 4 Cyl EFI | 40, 50, 60 | 4-Stroke | 10-79953Q04, 10-79953A2 | |
| Mercury | 6 Cyl Pro XS | 175, 200, 225, 250 | 4-Stroke | 10-79953Q04, 10-79953A2 | |
| MerCruiser | All | 1.5L, 2.5L, 3.0L | 10-79953Q04, 10-79953A2 | For sterndrive applications |
Technical Specs
- Product Type
- Gearcase Drain/Fill Plug
- Installation
- Threaded
- Connection
- Lower Unit Gearcase
- Housing Material
- Metal (Brass)
- Housing Color
- Silver/Metallic
- Fitting Type
- Screw with Gasket/Seal
- Thread Size
- 3/8-16
- Other Technical Attributes
- Includes sealing washer/gasket; used for both draining and filling gear oil in lower units; non-magnetic version
What’s in the Box
- 1 x Lower Unit Gear Lube Drain Plug (79953Q04)
- 1 x Seal/Gasket (included with assembly)
Installation Notes
- Position a suitable drain pan under the lower unit.
- Remove the lower (drain) screw first, followed by the upper (vent) screw to allow air to enter.
- Allow the gear lube to drain completely. Inspect the old oil for any signs of water intrusion or metal shavings.
- Install the new drain plug and gasket in the lower hole, but do not fully tighten yet.
- Using a gear lube pump, fill from the bottom hole until lubricant flows out of the top vent hole.
- Reinstall the upper vent screw and gasket, tightening it securely.
- Quickly remove the lube pump and install the lower drain screw, tightening it securely. Clean any excess lubricant.
Troubleshooting & FAQ
Will this plug fit my specific engine model?
This plug is designed for a wide range of Mercury and MerCruiser models. Please check the "Engine & Model Compatibility" and "Part Number Matrix" sections to confirm it matches your existing part number and engine series. Proper fitment is critical.
Is this drain plug magnetic?
No, this is a non-magnetic drain plug. It is designed to the specifications of OEM part number 10-79953Q04, which is also non-magnetic. It will not attract metallic particles from the gear oil.
What is the thread size of this plug?
The thread size is 3/8-16, which is standard for the specified Mercury and MerCruiser applications.
How often should I change the gearcase oil and the drain plug gasket?
You should follow your engine manufacturer’s recommended service interval, which is typically annually or every 100 hours of use. It is highly recommended to replace the drain plug gasket/seal with every oil change to prevent leaks.
What are the signs that my drain plug or seal is failing?
The most common sign of a failing seal is gear lube leaking from the drain or vent screw. This can appear as an oily sheen on the water or drips on the ground. A damaged or stripped plug will not tighten properly and must be replaced immediately.
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.
Payment & Security
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