Sierra Fuel Water Separator Filter Kit - Available as Standard Kit or Filter with Bonus Pack

The Sierra 18-7852 Fuel Water Separator Kit protects marine fuel systems by removing over 99.8% of emulsified water from gasoline before it reaches your engine. Rated at 21 microns and flowing up to 90 GPH, it is built to feed even high-demand motors while guarding sensitive inboard, sterndrive, and outboard fuel injection systems against water contamination and the corrosion, hesitation, and injector damage it can cause.

Each kit centers on a 1/4" filter element and includes the mounting hardware needed to add a water-separating stage to your fuel line. The Standard Kit pairs the filter with an 18-7853-1 mounting bracket for a straightforward installation, while the Filter with Bonus Pack version bundles in an 18-4256 pipe plug for a more complete setup. Both configurations use the same 18-7845 fuel filter element as the serviceable replacement cartridge going forward.

This kit is a Sierra-branded part built to OEM-equivalent specifications, making it a straightforward swap for factory-installed separators on compatible Mercury and Yamaha powered boats.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-7852
• Filtration Rating: 21 Micron
• Filter Size: 1/4"
• Flow Rate: 90 GPH
• Water Removal Efficiency: Removes over 99.8% of emulsified water from gasoline
• Housing Material: Aluminum (Standard Kit); Stainless Steel (Filter with Bonus Pack)
• Weight: 0.32 pounds (Standard Kit); 1 pound (Filter with Bonus Pack)
• Kit Contents: 18-7845 fuel filter and 18-7853-1 mounting bracket (Standard Kit); adds an 18-4256 pipe plug (Filter with Bonus Pack)
• OEM Cross-Reference: Mercury Marine 35-807172A4, 35-60494A4, 35-805369A4, 35-57250A1, 35-55501A1, 35-52456A1, 35-60494A1, 52444 (Standard Kit); Yamaha MAR-SEPAR-AT-OR (Filter with Bonus Pack)
• Application: Inboard, sterndrive, and outboard fuel injection systems

Sizes & Options

This kit is offered in two configurations under the same 18-7852 part family. Choose the Standard Kit if you need the core filter and mounting bracket for a new installation or bracket replacement. Choose the Filter with Bonus Pack version if you also need a pipe plug on hand for the install. Both use the same 1/4", 21 micron filter element.

Frequently Asked Questions

What does the Sierra 18-7852 fuel water separator kit do? It removes over 99.8% of emulsified water from gasoline before it reaches the engine, protecting inboard, sterndrive, and outboard fuel injection systems from water contamination. The Sierra 18-7852 kit is rated at 21 microns and flows at up to 90 GPH.

What is the difference between the Standard Kit and the Filter with Bonus Pack version? Both use the same 1/4", 21 micron filter and 18-7853-1 mounting bracket, but the Filter with Bonus Pack version of the 18-7852 kit also includes an 18-4256 pipe plug for a more complete installation.

What size filter does this kit use? The Sierra 18-7852 kit uses a 1/4" filter element rated at 21 microns in both the Standard Kit and Filter with Bonus Pack configurations.

What is included in the box? The Standard Kit includes an 18-7845 fuel filter and an 18-7853-1 mounting bracket. The Filter with Bonus Pack version includes those same two parts plus an 18-4256 pipe plug.

Is this compatible with Mercury or Yamaha engines? The Standard Kit cross-references to Mercury Marine numbers 35-807172A4, 35-60494A4, 35-805369A4, 35-57250A1, 35-55501A1, 35-52456A1, 35-60494A1, and 52444. The Filter with Bonus Pack version cross-references to Yamaha MAR-SEPAR-AT-OR.

How do I know which variant to order? Order the Standard Kit if you only need the filter and mounting bracket, or the Filter with Bonus Pack version of the 18-7852 if you also want an 18-4256 pipe plug included.

What material is the housing made of? The Standard Kit uses an aluminum housing, while the Filter with Bonus Pack version is listed with a stainless steel outer housing.

What flow rate does the 18-7852 filter support? It supports a flow rate of up to 90 GPH, which is sized to feed high-demand marine engines.

Does this filter work with fuel-injected engines? Yes, the Sierra 18-7852 is designed to prevent water damage to sensitive inboard, sterndrive, and outboard fuel injection systems.

Is this a genuine Sierra part? Yes, this is a genuine Sierra 18-7852 fuel water separator kit manufactured to OEM-equivalent specifications, not a generic aftermarket copy.

How much does each version weigh? The Standard Kit weighs 0.32 pounds and the Filter with Bonus Pack version weighs 1 pound.