Marine Lower Unit Oil Drain Plug - Fits Mercury/Mercruiser 40-115 HP (Replaces 10-79953Q2, 10-79953A2, 18-2244)

Marine Lower Unit Oil Drain Plug – Fits Mercury/Mercruiser 40-115 HP

This lower unit oil drain plug is designed for a direct fit on a wide range of Mercury and Mercruiser engines. It is compatible with most 40 HP to 115 HP outboards, as well as Bravo and Alpha One Gen 2 stern drives. This part serves as a direct replacement for multiple OEM part numbers, ensuring broad applicability.

Engineered from non-magnetic stainless steel, this drain plug screw provides a reliable seal to protect your lower unit gears from water intrusion and oil leaks. It is a crucial component for routine lower unit maintenance.

• Installation Method: Direct replacement screw with included gasket.
• Primary Materials: Stainless Steel Plug, Rubber/Nylon Gasket.
• Package includes two drain plugs and two matching gaskets.

Part Number Cross-Reference

Use this table to confirm equivalent part numbers across OEM and aftermarket brands.

Compatible Engine Models

Confirm your engine model/year in the table below. For Mercury owners, here’s a guide to help you identify your engine’s serial/model: Mercury Serial Number Guide. You can also review exploded diagrams to verify part numbers: Mercury Parts Diagrams & Catalog.

Technical Specifications

Package Contents

• 2 x Lower Unit Oil Drain Plug (Replaces 10-79953Q2)
• 2 x Gasket Seals

Installation Guide

1. Position a suitable oil drain pan under the lower unit.
2. Locate and remove the lower (drain) and upper (vent) plugs using a large flathead screwdriver.
3. Allow the gear lube to drain completely. Inspect the oil for any metal shavings or milky appearance, which can indicate internal issues.
4. Inspect the magnetic tip of the old drain plug for metal filings, a small amount is normal.
5. Clean the plug mounting surfaces on the gearcase.
6. Install the new gasket on the new lower drain plug.
7. Reinstall the new lower drain plug and tighten it securely. Do not overtighten.
8. Slowly fill the lower unit with the recommended marine gear lubricant through the lower drain hole until it flows out of the upper vent hole.
9. Install the new gasket on the upper vent plug and reinstall the plug, tightening securely.
10. Quickly remove the lubricant filler tube and reinstall the lower drain plug with its new gasket, tightening securely.
11. Wipe the lower unit clean and check for any leaks around both plugs.

Troubleshooting & FAQ

How do I confirm this plug fits my engine?
This plug fits Mercury/Mercruiser 40-115 HP outboards and Alpha One Gen 2 / Bravo sterndrives. The most reliable method is to cross-reference your existing part number with the numbers listed in our cross-reference table. Also, confirm the thread size is 3/8-16.

What is this plug made of?
The plug is made from high-quality, corrosion-resistant stainless steel. Its non-magnetic design ensures it will not interfere with any internal components.

How often should I replace the drain plug and gasket?
It is best practice to replace the drain plug gasket with every gear lube change to ensure a perfect seal. The plug itself should be replaced if it shows any signs of corrosion, damage, or stripped threads.

OEM vs. Aftermarket?
This listing is an aftermarket replacement part (not an OEM component). We build to OEM specifications using comparable-grade materials. Production is done in an ISO9002-certified facility, and each batch is inspected for consistent performance.

How fast do you ship and how much does it cost?
We offer fast global shipping—typically 5–15 days worldwide—and standard shipping is free. Expedited options are available at checkout depending on your location.

What is your warranty and return policy?
This product includes a 1-year warranty against manufacturing defects under normal use. If something goes wrong, contact our support team with your order details. Returns are accepted within our standard return window (unused & in original condition); please see our policy page or reach out for instructions.

Important Notes

• Verify that the product images and specifications, especially the 3/8-16 thread size, match your original part. If discrepancies exist—even if your model is listed—do not proceed with the purchase.
• This product is an aftermarket replacement part and is not an OEM component. Part numbers are used for reference purposes only.
• Professional installation is recommended to ensure safety and optimal performance. Overtightening can damage the gearcase.

Why Choose JLM MARINE?

• Quality Assured: As a trusted manufacturer for over 20 years, we supply top marine brands globally.
• Fast Global Shipping: Free delivery worldwide in 5–15 days.
• Direct from Manufacturer: Competitive pricing without compromising quality.