Exhaust Water Shutter/Flapper – Fits MerCruiser V6 & V8 Engines 1982–1987 (Replaces 99370A2)

Exhaust Water Shutter/Flapper – Fits MerCruiser V6 & V8 Engines 1982–1987 (Replaces 99370A2)

This exhaust water shutter is engineered to fit various MerCruiser V6 (4.3L) and V8 (5.0L, 5.7L) stern drive engines from 1982–1987 that are equipped with a 3-inch exhaust Y-pipe.

It serves as a direct replacement for Mercury Quicksilver 23-92852, Mercury 99370A2/92802, Sierra 18-2733, GLM 89160, and Mallory 9-42801.

• Prevents water from flowing back into the engine through the exhaust system.
• Designed for a secure fit in 3-inch exhaust Y-pipes.
• The complete kit includes one water shutter and two essential retainer grommets.

Part Number Cross-Reference

Use this table to confirm equivalent part numbers across OEM and aftermarket brands.

Compatible Engine Models

Confirm your engine model/year in the table below. For Mercury owners, here’s a guide to help you identify your engine’s serial/model: Mercury Serial Number Guide. You can also review exploded diagrams to verify part numbers: Mercury Parts Diagrams & Catalog.

Technical Specifications

Package Contents

• 1 x Water Shutter Flapper Kit (99370A2)
• 2 x Retainer Grommets

Installation Guide

1. Safety First: Ensure the engine is cool and disconnect the battery before starting.
2. Access the Y-Pipe: Locate the exhaust Y-pipe where it connects to the transom assembly. You may need to remove exhaust hoses for access.
3. Remove Old Shutter: Carefully pull out the old water shutter and its two retainer grommets from the Y-pipe housing. Take note of its orientation.
4. Clean Housing: Inspect and clean the inside of the Y-pipe housing, removing any debris or old rubber fragments.
5. Install New Grommets: Press the two new retainer grommets into the holes inside the Y-pipe housing.
6. Insert New Shutter: Position the new water shutter so the flapper hangs downward, and firmly press the ends of its steel rod into the new grommets until they snap into place.
7. Reassemble & Test: Reattach any exhaust hoses or components you removed. Reconnect the battery and briefly start the engine to check for proper function and ensure no exhaust leaks.

Troubleshooting & FAQ

Q: How do I know if this water shutter will fit my engine?
A: This shutter is designed for MerCruiser V6 (4.3L) and V8 (5.0L, 5.7L) stern drive engines made between 1982 and 1987 that use a 3-inch exhaust Y-pipe. Please cross-reference your existing part number with the numbers listed in our Part Number table to confirm compatibility.

Q: What are the signs of a failing exhaust water shutter?
A: Common signs include a rattling noise from the exhaust at idle, water ingestion leading to engine hydrolock (a severe issue), or visible damage and deterioration of the rubber flapper, such as cracking or stiffness.

Q: How often should I replace the exhaust water shutter?
A: It is recommended to inspect water shutters annually or every 100 hours of operation. They should be replaced immediately if they show any signs of wear, cracking, or damage to prevent catastrophic engine failure from water backflow.

Q: OEM vs. Aftermarket?
A: This listing is an aftermarket replacement part (not an OEM component). We build to OEM specifications using comparable-grade materials. Production is done in an ISO9002-certified facility, and each batch is inspected for consistent performance.

Q: How fast do you ship and how much does it cost?
A: We offer fast global shipping—typically 5–15 days worldwide—and standard shipping is free. Expedited options are available at checkout depending on your location.

Q: What is your warranty and return policy?
A: This product includes a 1-year warranty against manufacturing defects under normal use. If something goes wrong, contact our support team with your order details. Returns are accepted within our standard return window (unused & in original condition); please see our policy page or reach out for instructions.

Important Notes

• Verify that the product images and specifications match your original part. If discrepancies exist—even if your model is listed—do not proceed with the purchase.
• This product is an aftermarket replacement part and is not an OEM component.
• Professional installation is recommended to ensure safety and optimal performance.

Why Choose JLM MARINE?

• Quality Assured: As a trusted manufacturer for over 20 years, we supply top marine brands globally.
• Fast Global Shipping: Free delivery worldwide in 5–15 days.
• Direct from Manufacturer: Competitive pricing without compromising quality.