Sierra Powerhead Base Gasket 18-0333, Replaces Mercury 27-39401, Fits Mercury/Mariner Outboard Motors

The Sierra 18-0333 is a powerhead base gasket engineered as a direct replacement for Mercury Marine part number 27-39401. It is designed to fit Mercury and Mariner outboard motors, sealing the joint between the powerhead and the driveshaft housing to maintain proper compression and prevent water or exhaust leakage at this critical junction. A powerhead base gasket is a wear item that should be replaced any time the powerhead is removed for service, since reusing an old gasket can compromise the seal and lead to leaks or reduced performance.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-0333
• Product Type: Powerhead Base Gasket
• Weight: 0.05 pounds
• UPC: 030999873224

Fitment

• Mercury outboard motors
• Mariner outboard motors

Replaces (OEM)

• 27-39401

Frequently Asked Questions

What does the Sierra 18-0333 gasket fit? The Sierra 18-0333 powerhead base gasket is designed to fit Mercury and Mariner outboard motors.

What OEM part number does 18-0333 replace? It replaces Mercury Marine part number 27-39401.

Is the 18-0333 gasket the same as the OEM 27-39401 part? Yes, the Sierra 18-0333 is built to replace Mercury Marine 27-39401 as a direct equivalent for the powerhead base seal.

How much does the 18-0333 gasket weigh? The 18-0333 powerhead base gasket weighs 0.05 pounds.

Where is the powerhead base gasket installed? The 18-0333 is installed at the base of the powerhead, sealing the joint between the powerhead and the driveshaft housing on Mercury and Mariner outboard motors.

When should I replace the powerhead base gasket? The 18-0333 should be replaced any time the powerhead is removed from the driveshaft housing for service, since reusing the old gasket can result in a poor seal.

Does the 18-0333 gasket work on Mariner-branded outboards? Yes, the 18-0333 is designed to fit both Mercury and Mariner outboard motors.

What is the UPC for the Sierra 18-0333 gasket? The Sierra 18-0333 powerhead base gasket carries UPC 030999873224.

Is the 18-0333 a genuine Sierra part or a generic gasket? The 18-0333 is a Sierra-branded powerhead base gasket manufactured to replace Mercury Marine 27-39401.

What is included when I order the 18-0333? Ordering the 18-0333 gets you one Sierra powerhead base gasket sized to replace Mercury Marine 27-39401.