Gearcase Drain Plug with Gasket – Mercury/MerCruiser Applications, Replaces 10-79953Q04 and 10-79953A2
Gearcase Drain Plug with Gasket – Mercury/MerCruiser Applications, Replaces 10-79953Q04 and 10-79953A2 is backordered and will ship as soon as it is back in stock.
Worry-free returns
Worry-free returns
Shop with confidence. If you’re not completely satisfied, eligible items may be returned within the return window, provided they are unused and in original packaging.
If the return is due to our error or a defective item, we’ll make it right.
Please contact us before returning any item.
Delivery and Shipping
Delivery and Shipping
Orders are typically processed within 1–2 business days.
U.S. orders usually arrive within 6–15 days, depending on stock location and destination.
International delivery times may vary due to customs processing.
Tracking information will be provided once your order ships.
Gearcase Drain Plug with Gasket – Mercury/MerCruiser Applications, ...
Gearcase Drain Plug with Gasket – Mercury/MerCruiser Applications, Replaces 10-79953Q04 and 10-79953A2 is backordered and will ship as soon as it is back in stock.
Product Details
This gearcase drain plug with gasket is used to seal the lower-unit gearcase during gear-lubricant service. The plug uses a 3/8-16 thread and is listed for applicable Mercury and MerCruiser marine gearcase and sterndrive applications.
Use the existing plug, gasket, engine model, serial number, and gearcase configuration to confirm fitment before ordering. The cataloged replacement references include Mercury part numbers 10-79953Q04, 10-79953A2, and related numbers listed below.
- 3/8-16 threaded gearcase drain/fill plug.
- Includes one sealing gasket for installation.
- Designed for use during lower-unit gear-lubricant draining and refilling.
- Aftermarket replacement; Mercury and MerCruiser names and part numbers are used only to identify application and reference compatibility.
Part Number Matrix
These are replacement and interchange references identified in the available marine-parts catalog data. Always compare the original part and application details before installation.
| Brand or Reference | Part Number | Reference Type |
|---|---|---|
| Mercury Marine | 10-79953Q04 | OEM reference |
| Mercury Marine | 10-79953A2 | OEM reference |
| Mercury Marine | 10-79953Q2 | OEM reference |
| Mercury Marine | 10-79953 | OEM reference |
| Mercury Marine | 10-20259 | OEM reference |
| Mercury Marine | 10-28634, 10-28634A1 | OEM references |
| Sierra | 18-2244 | Aftermarket replacement reference |
| Additional references | 816610A1, 816610A2, F40109, 10-F50109 | Replacement references |
Engine & Model Compatibility
Available catalog information identifies this 3/8-16 drain plug for applicable Mercury/Mariner outboard drive-system and MerCruiser-related gearcase applications. The references are not a substitute for an exact model, year, serial-number, or gearcase check.
| Application Family | Component Area | Thread | Fitment Guidance |
|---|---|---|---|
| Mercury/Mariner outboard | Lower-unit gearcase drive system | 3/8-16 | Confirm the original plug and serial-number range before ordering. |
| Mercury/MerCruiser marine applications | Gearcase or sterndrive lubricant service | 3/8-16 where specified | Verify the exact gearcase assembly and gasket arrangement. |
Important: A part-number match is the safest way to confirm fitment. Do not rely on horsepower alone, because model, year, serial number, gearcase design, and service configuration may affect compatibility.
Technical Specs
- Product Type
- Gearcase drain/fill plug
- Installation
- Threaded screw-in installation
- Connection
- Lower-unit gearcase or applicable sterndrive gearcase
- Thread Size
- 3/8-16
- Seal
- Sealing gasket included
- Product Classification
- Aftermarket replacement
- Primary Function
- Seals the gearcase opening during gear-lubricant service
What’s in the Box
- 1 x Gearcase drain/fill plug
- 1 x Sealing gasket
Installation Notes
- Place a suitable drain pan beneath the lower unit or sterndrive gearcase.
- Remove the lower drain plug first, then remove the upper vent or level plug where applicable.
- Allow the old gear lubricant to drain completely. Inspect it for water contamination or abnormal metal debris.
- Clean the sealing surface and install the new gasket with the replacement plug.
- Use the correct marine gear-lubricant pump and fill the gearcase according to the engine or drive manufacturer’s service procedure.
- Install and tighten the upper vent or level plug, if fitted.
- Remove the lubricant pump and promptly install the lower plug with its gasket. Tighten using the manufacturer’s specified torque.
- Clean excess lubricant and check for leaks before returning the vessel to service.
Do not reuse a damaged, crushed, or hardened gasket. Do not overtighten the plug, as damaged threads or a distorted sealing surface may cause leakage.
Troubleshooting & FAQ
How do I confirm that this plug fits my engine?
Compare the original plug’s thread, dimensions, sealing arrangement, and part number. Confirm the engine or sterndrive model, year, and serial-number range using the manufacturer’s parts information. The listed OEM references are useful for comparison but do not confirm every Mercury or MerCruiser application.
What is the thread size?
The cataloged thread size is 3/8-16.
Is a gasket included?
Yes. This listing includes one sealing gasket for the supplied plug.
Can I reuse the old gasket?
Replacing the gasket during gearcase service is recommended. A reused or damaged gasket may not seal correctly and can allow water or lubricant leakage.
What lubricant-service procedure should I use?
Follow the service procedure and torque specifications for your specific engine or sterndrive. In general, gear lubricant is commonly drained through the lower opening and filled from the lower opening until it reaches the specified level or exits the upper vent opening.
Is this an OEM Mercury part?
No. This is an aftermarket replacement. Mercury, MerCruiser, Mariner, and the referenced OEM numbers are provided only for application and interchange identification.
What if the plug does not thread in smoothly?
Stop installation. Do not force or cross-thread the plug. Check the thread size, gasket position, and gearcase opening, and compare the replacement with the original part before continuing.
Safety & Important Info
- Confirm the exact part-number and application match before purchase and installation.
- Use only lubricant specified for your particular lower unit or sterndrive.
- Inspect the plug threads and sealing surface before installation.
- Use the manufacturer’s specified tightening torque; overtightening can damage the gearcase.
- Professional installation is recommended when the application or service procedure is uncertain.
About Sea Sierra
- Marine Replacement Parts — Practical replacement components for common marine service and repair needs.
- Application-Focused Information — Reference numbers and installation guidance are provided to help customers compare parts accurately.
- Service-Minded Support — Verify the original part and application details before ordering whenever fitment is critical.
Payment & Security
Payment methods
Your payment information is processed securely. We do not store credit card details nor have access to your credit card information.
