Lower Unit Oil Drain Plug Screw Kit – Fits Mercury/MerCruiser Outboard & Sterndrive (Replaces 79953Q04, 816610A1)

$12.00 $19.00

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Lower Unit Oil Drain Plug Screw Kit – Fits Mercury/MerCruiser Outboard & Sterndrive (Replaces 79953Q04, 816610A1) is backordered and will ship as soon as it is back in stock.

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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.).

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Delivery and Shipping

Free standard shipping on all orders under 1 KG

If you have any questions, feel free to email us at info@sierramarines.com, and we’ll get back to you within 20–36 hours.

Product Details

This Lower Unit Oil Drain Plug Screw Kit is designed for a wide range of Mercury/MerCruiser applications, including Alpha One (Gen I & II), I, R, MR, TR, and TRS sterndrives. It also fits all Mercury outboard models that use 3/8-16 non-magnetic drain/fill screws, as well as compatible Johnson/Evinrude and Chrysler/Force/US Marine outboards.

This kit serves as a direct replacement for multiple OEM part numbers, including Mercury 79953Q04, Johnson/Evinrude 307552, Sierra 18-2244, and Mallory 9-72650, providing a reliable aftermarket alternative.

Crafted from durable non-magnetic metal suitable for marine environments.
Features a 3/8-16 UNC thread for manual installation with a secure gasket seal.
Complete kit includes two drain plug screws and two matching yellow gaskets.

Part Number Matrix

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

Brand	Part Number
Mercury/MerCruiser	79953Q04
Mercury/MerCruiser	816610A1
Mercury/MerCruiser	28634
Mercury/MerCruiser	28634A1
Mercury/MerCruiser	79953
Mercury/MerCruiser	79953A2
Mercury/MerCruiser	79953Q2
Sierra	18-2244
Mallory	9-72650
Johnson/Evinrude	307552
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 plug fits most outdrives and outboards with 3/8-16 drain screws, excluding the Verado series. Please verify your specific model in the table.

For Johnson/Evinrude and Chrysler/Force/US Marine owners: This plug is compatible with all outboard models that utilize a 3/8-16 non-magnetic drain plug screw.

Brand	Model	Application	Years	OEM Part No.	Notes
Mercury	I, R, MR Sterndrives	All	All	79953Q04	Non-magnetic
Mercury	Alpha One	Upper & Lower Units	All	79953Q04	Non-magnetic
Mercury	Gen II	Upper & Lower Units	All	79953Q04	Non-magnetic
Mercury	TR, TRS	All	All	79953Q04	Non-magnetic
Mercury	Outboards	All with 3/8-16 drain plugs	All	79953Q04	Except Verado series
Mercury	30/40 EFI (3 CYL)	4-Stroke	All	79953Q04
Mercury	40/50/60 EFI (4 CYL)	4-Stroke	All	79953Q04	Includes Jet 40
Mercury	Formula 60	4-Stroke	All	79953Q04
Mercury	75/90/115/125 DFI	1.5L (3 CYL)	All	79953Q04	Includes 80 Jet
Mercury	115 Pro XS	1.5L (3 CYL)	All	79953Q04
Mercury	135/150/175 DFI	2.5L	All	79953Q04	Includes 110 Jet
Mercury	150/175 Pro XS	2.5L	All	79953Q04
Mercury	200XS DFI	2.5L ROS	All	79953Q04
Mercury	200 DFI Jet Drive	All	All	79953Q04	Includes powerhead & pump
Mercury	225/250 Pro XS	3.0L DFI	All	79953Q04
Mercury	225/250 Sport XS	3.0L DFI	All	79953Q04
Mercury	540 Stroker 4V	All	All	79953Q04
Mercury	Vazer	All	All	79953Q04	Transom and drive applications
Johnson/Evinrude	Outboards	All with 3/8-16 drain plugs	All	307552	Non-magnetic
Chrysler/Force/US Marine	Outboards	All with 3/8-16 drain plugs	All	19183, F50556, F8077, F8186	Non-magnetic

Technical Specs

Product Type: Lower Unit Oil Drain/Fill Plug Screw Kit
Installation: Manual thread-in with gasket seal
Material: Non-Magnetic metal
Thread Size: 3/8-16 UNC
Weight: 0.01 kg (0.317 oz)
Quantity Per Pack: 2 pcs (screw and gasket)
Color: Silver/metallic with yellow gasket
Package Dimensions: 3.82 × 2.68 × 0.43 inches (97 × 68 × 11 mm)
Application: Gear lube drain or fill hole plug

What’s in the Box

2 x Drain Plug Screw (Non-magnetic)
2 x Drain Plug Gasket (Yellow)

Installation Notes

Remove the top (vent) plug first.
Remove the bottom drain plug to allow the old oil to drain completely.
Using a gear lube pump, fill from the bottom hole until new lube flows out of the top vent hole.
Quickly replace the top (vent) plug first, then install the bottom drain plug to minimize oil loss.
Ensure both plugs are torqued to manufacturer specifications to prevent leaks.

Troubleshooting & FAQ

What engines does this drain plug kit fit?

This kit is designed for Mercury/MerCruiser sterndrives (Alpha One, Gen II, I, R, MR, TR, TRS), most Mercury outboards, and all Johnson/Evinrude and Chrysler/Force/US Marine outboards that use a 3/8-16 UNC non-magnetic drain screw.

How do I know if this is the right plug for my engine?

The best way to confirm is to check your service manual or the original part for the 3/8-16 thread size. This is a non-magnetic screw kit, specified for certain gearcases to avoid interfering with internal components. If your model is listed in the compatibility chart, it is a confirmed fit.

Is this a magnetic or non-magnetic drain plug?

This is a non-magnetic drain plug screw kit. It is critical for applications where a magnetic screw is not specified, as a magnetic plug could cause issues in certain lower units.

How often should I replace the drain plug gasket?

It is strongly recommended to use a new gasket every time you change your gear lube. This ensures a tight, leak-proof seal. This kit conveniently includes two new gaskets with the screws.

What are the signs of a failing drain plug or gasket?

Common signs include visible gear oil seeping from the drain or vent holes, stripped threads on the screw or in the housing, or the screw not tightening properly. A milky or cloudy appearance in your old gear lube indicates water has entered the gearcase, often due to a poor seal.

What is the thread size of these screws?

The screws in this kit have a 3/8-16 UNC thread size, which is a common standard for many outboard and sterndrive lower units.

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.

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