Sierra Oil Seal 18-0595, Replaces Mercury Marine 26-66303

The Sierra 18-0595 is an oil seal engineered for Mercury outboard powerheads, providing a reliable barrier against oil leakage at the shaft. It is built with a 1.125 inch outer diameter and a 0.688 inch shaft size, sized to fit precisely into the powerhead seal bore it is designed for. At only 0.250 inches wide, it is a compact component intended to sit flush within its mounting location without interference from surrounding parts.

This seal directly replaces Mercury Marine part number 26-66303, making it a straightforward drop-in option for powerhead seal replacement and rebuild work. Sierra parts are constructed with quality materials aimed at delivering dependable service life and consistent sealing performance in the marine environment. The 18-0595 falls under Sierra's Mercury Outboard Powerhead Seals & O-Rings category, reflecting its specific application in outboard powerhead assemblies where maintaining oil containment is critical to engine protection.

At just 0.02 pounds, this is a small, lightweight part that is easy to keep on hand as a maintenance spare. Whether performing a full powerhead rebuild or addressing an isolated oil seal failure, the 18-0595 gives technicians and boat owners a Sierra-manufactured alternative to the OEM Mercury Marine part.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-0595
• Product Name: Oil Seal
• Category: Mercury Outboard Powerhead Seals & O-Rings
• Outer Diameter: 1.125 inches
• Shaft Size: 0.688 inches
• Width: 0.250 inches
• Weight: 0.02 pounds
• UPC: 808282233983
• OEM Cross-Reference: Mercury Marine 26-66303

Fitment

• Mercury outboard powerheads using Mercury Marine oil seal 26-66303

Replaces (OEM)

• 26-66303

Frequently Asked Questions

What does the Sierra 18-0595 oil seal replace? The Sierra 18-0595 directly replaces Mercury Marine part number 26-66303, so it can be installed anywhere that Mercury Marine seal is called for.

What is the outer diameter of the 18-0595 oil seal? The outer diameter is 1.125 inches, which is the size of the seal's outer edge that seats into the powerhead bore.

What shaft size does this Sierra oil seal fit? It is sized for a 0.688 inch shaft, matching the shaft diameter it seals against on Mercury outboard powerheads.

How wide is the Sierra 18-0595 seal? 0.250 inches wide, a compact dimension intended to fit flush within its designated seal location.

How much does the 18-0595 oil seal weigh? It weighs 0.02 pounds, a very light single-component part.

What is the UPC for the Sierra 18-0595? The UPC is 808282233983, which can be used to confirm you are ordering the correct oil seal.

Is the Sierra 18-0595 an OEM part or an aftermarket replacement? It is a Sierra-manufactured replacement seal built to replace Mercury Marine 26-66303, not an OEM Mercury Marine part itself, though it is designed as a direct equivalent.

What application is the 18-0595 oil seal used on? It is listed under Mercury Outboard Powerhead Seals & O-Rings, indicating its use in Mercury outboard powerhead assemblies.

What is included when you order the 18-0595? Each order includes one Sierra 18-0595 oil seal.

Is the Sierra 18-0595 suitable for a powerhead rebuild? Yes, its role as a powerhead seal replacing Mercury Marine 26-66303 makes it applicable to powerhead rebuild and repair work.