Washer Drain/Fill Plug Pack of 5 | Sierra 18-4248-9

Sierra 18-4248-9 Drain/Fill Plug Washer | Pack of 5 | Plastic | OMC, Johnson, Evinrude | Replaces OMC 311598, Mallory 9-60408

The Sierra #18-4248-9 is a plastic drain/fill plug washer for OMC, Johnson, and Evinrude outboard and sterndrive lower unit drain and fill plugs. Sold as a pack of 5 washers. Replaces OMC/Johnson/Evinrude 311598 and Mallory 9-60408.

Product Details:

• Part Number: 18-4248-9 (Sierra)
• SKU: SIERRA-18-4248-9
• Manufacturer: Sierra
• Type: Drain/Fill Plug Washer — Plastic
• Pack: 5 washers
• Application: OMC, Johnson, Evinrude outboard and sterndrive lower unit drain and fill plugs
• Replaces: OMC/Johnson/Evinrude 311598; Mallory 9-60408
• Condition: New

Cross-Reference — Replaces:

• OMC / Johnson / Evinrude: 311598
• Mallory: 9-60408

Additional Information

Drain/Fill Plug Washer — Function and Why It Matters:

The drain/fill plug washer seals the lower unit drain and fill plug threads against gear lube leakage. The washer creates a compression seal between the plug head and the gearcase housing seating surface when the plug is torqued. Without an intact washer — or with a cracked, deformed, or missing one — the plug cannot seal reliably, and gear lube will seep or leak from the gearcase over time. On OMC, Johnson, and Evinrude lower units, the drain and fill plugs each require their own washer; a complete gear lube service requires two washers per service (one drain, one fill).

Replace at Every Gear Lube Service:

Plastic plug washers compress and deform slightly when torqued. Re-using a previously compressed washer risks inadequate sealing and gear lube loss between service intervals. Best practice is to install new washers at every gear lube change — at $8.95 for a pack of 5, each washer costs less than $1.80, making annual replacement the lowest-cost insurance against a gear lube leak on a Johnson or Evinrude lower unit. A pack of 5 provides two complete gear lube services plus one spare.

Plastic Washer — Material and Torque:

The 18-4248-9 uses a plastic (nylon or similar polymer) washer rather than a fiber or aluminum washer. Plastic washers provide adequate sealing under the correct torque specification for OMC, Johnson, and Evinrude drain and fill plugs. Do not overtighten — overtorquing a plastic washer crushes it beyond its sealing geometry and can strip the aluminum gearcase housing threads. Tighten drain and fill plugs to the torque specification in the OMC/Johnson/Evinrude service manual for your specific outboard or sterndrive model.

OMC Sterndrive and Outboard — Coverage:

OMC part number 311598 was used across Johnson and Evinrude outboard models and OMC sterndrive lower units that share the same drain and fill plug washer specification. Confirm your specific engine model uses the 311598 washer by cross-referencing your engine's parts list before ordering.

Installation Notes:

• Install new washers at every gear lube change — do not reuse previously compressed washers
• One washer per plug — a complete gear lube service requires one drain plug washer and one fill plug washer
• Tighten plugs to the torque specification in your service manual — do not overtighten plastic washers
• Inspect gearcase housing seating surface for corrosion or damage before installing new plugs
• Check for gear lube leakage around drain and fill plugs after first use following gear lube service

Frequently Asked Questions

1. How many washers do I need per gear lube service?
Two — one for the drain plug and one for the fill plug. A pack of 5 covers two complete gear lube services with one spare washer.

2. Can I reuse the old washer?
Not recommended — plastic washers compress under torque and may not seal reliably when reused. Replace both washers at every gear lube change.

3. What OMC, Johnson, or Evinrude part number does this replace?
OMC/Johnson/Evinrude 311598 and Mallory 9-60408.

4. How tight should I torque the drain and fill plugs?
Refer to the torque specification in your OMC, Johnson, or Evinrude service manual for your specific model. Overtightening crushes the plastic washer and risks stripping the aluminum gearcase housing threads.

5. Will a gear lube leak occur if the washer is missing or damaged?
Yes — a missing, cracked, or deformed washer allows gear lube to seep from around the plug threads over time. Replace washers at every gear lube service to ensure a reliable seal.