Gearcase Drain Plug – Fits Mercury/MerCruiser (Replaces 10-79953Q04, 79953Q04)
Gearcase Drain Plug – Fits Mercury/MerCruiser (Replaces 10-79953Q04, 79953Q04) 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 – Fits Mercury/MerCruiser (Replaces 10-79953Q04...
Gearcase Drain Plug – Fits Mercury/MerCruiser (Replaces 10-79953Q04, 79953Q04) is backordered and will ship as soon as it is back in stock.
Product Details
This replacement Gearcase Drain Plug – Fits Mercury/MerCruiser Marine Engines is designed for various Mercury outboard engines, including 30-125 HP EFI models, and MerCruiser sterndrive lower units. It ensures a secure seal for the gearcase, preventing oil leaks and water intrusion.
This part is a direct interchange for Mercury part numbers 10-79953Q04, 79953Q04, 10-79953A2, 10-79953Q2, and aftermarket number 18-2244.
- Features a threaded design for straightforward installation.
- Functions as both the drain and fill screw for the lower unit gear oil.
- Includes the required sealing washer for a leak-proof fit.
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 |
| Aftermarket | 18-2244 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
Fits various Mercury outboard engines, including 30, 40, 75, 80, 90, 115, and 125 HP EFI models, as well as select MerCruiser sterndrive lower units.
| Brand | Model | Rated HP | OEM Part No. | Notes |
|---|---|---|---|---|
| Mercury | EFI Outboards | 30, 40, 75, 80, 90, 115, 125 | 10-79953Q04 | 3 Cyl EFI models |
| Mercury/MerCruiser | Various Sterndrive/Outdrive | 10-79953Q04 | Used in gearcase/lower unit |
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
- Other Technical Attributes
- Includes sealing washer/gasket; used for both draining and filling gear oil in lower units
What’s in the Box
- 1 x Lower Unit Gear Lube Drain w/Fill Hole Screw (79953Q04)
- 1 x Seal/Gasket (included with assembly)
Installation Notes
- Position a suitable drain pan below the lower unit gearcase.
- Slowly remove the upper vent screw, then remove the lower drain screw to begin draining the oil.
- Allow all old gear lube to drain completely.
- Clean the threads around the drain and vent holes.
- Install the new drain screw with its gasket in the lower hole, tightening it securely but without over-torquing.
- Fill the gearcase with the manufacturer-recommended lubricant through the upper vent hole until fluid begins to seep out.
- Reinstall the upper vent screw with its seal and wipe away any excess oil.
Troubleshooting & FAQ
How do I know if this drain plug fits my engine?
This plug is compatible with many Mercury EFI outboards (30-125 HP) and MerCruiser sterndrives. To confirm your fitment, please review the part numbers in the Part Number Matrix or check your engine’s service manual for part number 10-79953Q04.
What are the signs my old drain plug needs replacing?
Common signs of failure include a stripped screw head that prevents proper tightening, visible thread damage, or a persistent gear lube leak from the drain hole, which often indicates a worn or compressed seal.
Do I need to replace the seal every time I change the gear lube?
Yes, it is best practice to replace the sealing washer each time you remove the drain plug. This ensures a proper, leak-free seal and protects your gearcase from water intrusion. This product includes a new seal for your convenience.
Can this screw be used for both the upper vent and lower drain holes?
Yes, on most compatible models, this screw is interchangeable and can be used for both the lower drain/fill location and the upper vent hole on the gearcase.
What is the difference between an OEM and an aftermarket part?
This listing is an aftermarket replacement (not OEM). It is built to OEM-level specifications with comparable materials. All parts are manufactured in an ISO 9002 facility and batch-inspected for consistency and quality.
What are your shipping speeds and costs?
We ship worldwide quickly—typical transit time is 5–15 days. Standard shipping is free for most orders, with expedited options available at checkout where applicable.
What is your warranty and return policy?
This product is covered by a 1-year warranty against manufacturing defects under normal marine use. If you encounter any issues, please contact our support team with your order details. Returns are accepted within our standard window for items that are unused and in original condition.
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
Payment methods
Your payment information is processed securely. We do not store credit card details nor have access to your credit card information.
