Water Exhaust Shutter – Fits MerCruiser V6/V8 Stern Drives (Replaces 99370A2)

Water Exhaust Shutter – Fits MerCruiser V6/V8 Stern Drives (Replaces 99370A2)

This water exhaust shutter fits MerCruiser 4.3L V6, 5.0L V8, and 5.7L V8 engines with center riser manifolds, produced between 1982 and 1987. It is designed to install in the exhaust Y-pipe, where its primary function is to prevent water from flowing back into the exhaust manifold and engine cylinders. This is a critical component for protecting your engine from water ingestion, especially during deceleration or when the stern is low in the water.

This part serves as a direct replacement for several OEM and aftermarket part numbers, ensuring compatibility and a proper fit for the specified engine models.

• Installation Location: Installs inside the exhaust Y-pipe.
• Primary Function: Prevents water backflow into the engine.
• Construction: Made from durable rubber with a steel rod hinge for longevity.

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 Exhaust Shutter (99370A2)

Installation Guide

1. Ensure the engine is off and cool, and disconnect the battery for safety.
2. Locate the exhaust Y-pipe at the rear of the engine assembly.
3. You may need to remove the exhaust bellows or related components to access the shutter.
4. Carefully remove the old, worn-out shutter from its mounting point within the Y-pipe.
5. Thoroughly clean the interior of the pipe where the shutter sits to remove any debris or corrosion.
6. Position the new shutter correctly, ensuring its hinge mechanism moves freely.
7. Reinstall any components that were removed to gain access.
8. Reconnect the battery, start the engine, and check for any unusual exhaust noises.

Troubleshooting & FAQ

Q: How do I confirm this fits my engine?
A: This shutter is for MerCruiser 4.3L V6, 5.0L V8, and 5.7L V8 engines (1982–1987) with center riser manifolds. Please verify your engine model and year against the compatibility list and ensure your current part number matches 99370A2 or its aftermarket equivalents.

Q: What are the signs of a failing exhaust shutter?
A: Common symptoms include a distinct rattling or clanking sound from the exhaust system at idle, water ingestion into the engine cylinders (which can cause severe damage), or visible cracks and deterioration of the old rubber flapper.

Q: How is this part different from the OEM version?
A: Our aftermarket shutter is designed to meet or exceed original equipment specifications for fit, form, and function. It is made with high-quality rubber and steel materials to ensure reliable performance in a marine environment.

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.