O-Ring Drain Screw | Sierra 18-4253-9

Sierra 18-4253-9 Drain Screw O-Ring | Pack of 5 | OMC, Johnson, Evinrude | Replaces OMC 336982, Mallory 9-76653

The Sierra #18-4253-9 is a drain screw O-ring for OMC, Johnson, and Evinrude outboard and sterndrive lower units. Sold as a pack of 5 O-rings. Replaces OMC/Johnson/Evinrude 336982 and Mallory 9-76653.

Product Details:

• Part Number: 18-4253-9 (Sierra)
• SKU: SIERRA-18-4253-9
• Manufacturer: Sierra
• Type: Drain Screw O-Ring
• Pack: 5 O-rings
• Application: OMC, Johnson, Evinrude outboard and sterndrive lower unit drain screws
• Replaces: OMC/Johnson/Evinrude 336982; Mallory 9-76653
• Condition: New

Cross-Reference — Replaces:

• OMC / Johnson / Evinrude: 336982
• Mallory: 9-76653

Additional Information

Drain Screw O-Ring — Function:

Some OMC, Johnson, and Evinrude lower unit drain and fill plugs use an O-ring groove on the plug body rather than a flat washer seating surface to seal against the gearcase housing. The O-ring compresses into its groove when the screw is tightened, forming a reliable radial seal between the plug body and the gearcase bore. A damaged, hardened, or missing O-ring allows gear lube to seep from around the plug body threads or groove, leading to gear lube loss between services.

O-Ring vs. Flat Washer — Know Your Plug Type:

OMC, Johnson, and Evinrude lower units use two distinct drain/fill plug sealing designs across different models:

• Flat washer type — uses a plastic or fiber washer under the plug head that compresses against a flat seating surface on the gearcase housing (see Sierra 18-4248-9)
• O-ring type — uses an O-ring in a groove on the plug body that seals against the gearcase bore (this product, 18-4253-9)

Confirm which sealing type your drain and fill plugs use by inspecting the plugs removed from your lower unit before ordering. Installing a washer on an O-ring plug or vice versa will not seal correctly.

Replace at Every Gear Lube Service:

O-rings harden, compress-set, and lose elasticity over time and with heat cycling. A reused O-ring that has been previously compressed may not return to full cross-section and can fail to seal reliably after reinstallation. Replace the drain screw O-ring at every gear lube service. At $2.95 for a pack of 5 — under $0.60 per O-ring — annual replacement is the lowest-cost protection against a gear lube leak on an OMC, Johnson, or Evinrude lower unit. A pack of 5 provides two complete gear lube services (drain + fill O-ring each) with one spare.

Installation Notes:

• Confirm your drain and fill plugs use O-ring sealing (not flat washer) before ordering — inspect removed plugs
• Install new O-rings at every gear lube change — do not reuse previously compressed O-rings
• One O-ring per plug — a complete gear lube service requires one drain screw O-ring and one fill screw O-ring
• Seat O-ring fully in the plug groove before threading into gearcase — a displaced O-ring will not seal
• Tighten plugs to the torque specification in your OMC/Johnson/Evinrude service manual — do not overtighten
• Check for gear lube seepage around plugs after first use following gear lube service

Frequently Asked Questions

1. How do I know if my drain plug uses an O-ring or a flat washer?
Remove the drain plug and inspect it — O-ring plugs have a groove machined into the plug body that holds the O-ring; flat washer plugs have a flat shoulder under the plug head with no groove. Order the correct sealing type for your plug design.

2. How many O-rings do I need per gear lube service?
Two — one for the drain screw and one for the fill screw. A pack of 5 covers two complete gear lube services with one spare.

3. Can I reuse the old O-ring?
Not recommended — O-rings compress-set and harden with heat cycling and may not return to full cross-section after removal. Replace at every gear lube change.

4. What OMC, Johnson, or Evinrude part number does this replace?
OMC/Johnson/Evinrude 336982 and Mallory 9-76653.

5. What is the difference between this O-ring (18-4253-9) and the plug washer (18-4248-9)?
The 18-4253-9 is an O-ring for plugs with a groove on the plug body. The 18-4248-9 is a flat plastic washer for plugs with a flat seating surface under the plug head. Inspect your drain and fill plugs to confirm which sealing design your lower unit uses before ordering.