Lower Unit Drain Plug Gearcase Screw – Fits Mercury & MerCruiser (Replaces 10-79953Q04, 18-2244)

$10.27

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Lower Unit Drain Plug Gearcase Screw – Fits Mercury & MerCruiser (Replaces 10-79953Q04, 18-2244) is backordered and will ship as soon as it is back in stock.

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Product Details

This non-magnetic Lower Unit Drain Plug Gearcase Screw with an integrated seal is designed for Mercury and Mariner outboards equipped with a 3/8-16 drain and fill hole. It is also compatible with all MerCruiser stern drives, with the exception of the Verado series. The high-quality construction prevents gear lube leakage and water intrusion into the gearcase, protecting vital components.

It serves as a direct replacement for various part numbers, including Mercury 10-79953Q04, Johnson/Evinrude 307552, and Mallory 60101.

Constructed from high-grade non-magnetic stainless steel for maximum corrosion resistance.
Features a 3/8-16 thread with an included seal for a secure, leak-free fit.
Installation is straightforward and requires only a standard flat blade screwdriver.

Part Number Matrix

Use this matrix to confirm equivalent references across OEM and aftermarket.

Brand	Part Number
Mercury	10-79953Q04
Mercury	10-79953A2
Mercury	10-79953Q2
Mercury	18-2244
Mercury	22420
Johnson/Evinrude	307552
Mallory	60101
Mallory	60102
Chrysler/Force/US Marine	19183
Chrysler/Force/US Marine	F50556
Chrysler/Force/US Marine	F8077
Chrysler/Force/US Marine	F8186

Engine & Model Compatibility

Confirm your engine model/year in the table below.

For Mercury/MerCruiser Owners: This part fits a wide range of outboard and sterndrive models as detailed below. Key applications include Alpha One drives and various EFI, DFI, and Pro XS outboards.

For Mariner Owners: Fits most outboards using a 3/8-16 drain plug screw. Please verify your specific model's requirements.

Brand	Model	Rated HP	Stroke	OEM Part No.	Notes
Mercury	MerCruiser I R MR Alpha 1 TR TRS			10-79953Q04	Non-magnetic version
Mercury	All outboards with 3/8-16 drain hole	40-250		10-79953Q04	Except Verado series
Mercury	40, 50, 60, JET 40 EFI	40-60	4-Stroke	10-79953Q04	4-Cylinder models
Mercury	30/40 EFI	30-40	4-Stroke	10-79953Q04	3-Cylinder models
Mercury	VAZER		4-Stroke	10-79953Q04	All VAZER models
Mercury	75, 80, 90, 115, 125 DFI	75-125		10-79953Q04	1.5L (3-Cylinder) models
Mercury	115 Pro XS	115		10-79953Q04	1.5L (3-Cylinder) models
Mercury	135, 150, 175 DFI	135-175		10-79953Q04	2.5L models
Mercury	150, 175, 200 Pro XS	150-200		10-79953Q04	2.5L models
Mercury	225, 250 Pro XS	225-250		10-79953Q04	3.0L DFI models
Mercury	200 DFI JET DRIVE	200		10-79953Q04	Powerhead and pump
Mercury	540 Stroker 4V			10-79953Q04	Performance model
Mariner	Outboards with 3/8-16 drain hole				Non-Verado models
Johnson/Evinrude				307552
Chrysler/Force/US Marine				19183/F50556/F8077/F8186

Technical Specs

Product Type: Lower Unit Drain/Fill Plug Screw with Seal
Installation: Manual (requires flat blade screwdriver)
Connection: 3/8-16 thread
Housing Material: Non-magnetic metal (stainless steel)
Housing Color: Silver/metallic
Fitting Type: Threaded plug with seal gasket
Thread Size: 3/8-16
Other Technical Attributes: Non-magnetic version; prevents gear lube leakage and water intrusion

What’s in the Box

2 x Lower Unit Drain Plug Gearcase Screw with Seal (10-79953Q04)

Installation Notes

Position a suitable drain pan underneath the lower unit's drain screw.
Using a large flat blade screwdriver, carefully remove the old drain plug and allow all gear lube to drain completely.
Inspect the old lube for any signs of water (milky color) or metal shavings.
Clean the threads around the drain hole to ensure a good seal.
Install the new drain plug screw with its seal. Ensure it is threaded correctly by hand before tightening.
Tighten the screw securely until the seal is compressed. Do not overtighten, as this can damage the gearcase or the plug.
Remove the upper (vent) screw and refill the lower unit with the manufacturer-recommended gear lube until it flows out of the vent hole.
Reinstall the vent screw and clean any excess lube from the housing. Check for leaks around the drain plug after a short period.

Troubleshooting & FAQ

How do I confirm this plug fits my specific engine?

The best method is to cross-reference your original part number with our Part Number Matrix. Additionally, review the Engine & Model Compatibility table. This plug fits most Mercury, MerCruiser, and Mariner units with a 3/8-16 thread drain hole, but it's crucial to verify your model is listed and that it is not part of the Verado series.

Why is a non-magnetic plug recommended?

Standard magnetic plugs are designed to attract metallic debris in the gear lube. However, non-magnetic stainless steel plugs like this one offer superior corrosion resistance in saltwater and freshwater environments. This prevents the plug itself from rusting or seizing, making future maintenance easier.

When should I replace the drain plug and seal?

It is best practice to replace the drain plug seal (gasket) every time you change your gear lube to ensure a perfect seal. The entire screw should be replaced if the head is stripped, the threads are damaged, or if it shows significant corrosion.

What are signs of a failing drain plug seal?

The most common sign is a "milky" or creamy appearance in your gear lube, which indicates water has intruded into the gearcase. You may also notice gear lube leaking from around the drain screw, which signals a compromised 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

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