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Water Exhaust Shutter – Fits MerCruiser V6/V8 Engines 4.3L, 5.0L, 5.7L (Replaces 99370A2)
- $19.99
$23.00- $19.99
- Unit price
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Water Exhaust Shutter – Fits MerCruiser V6/V8 Engines 4.3L, 5.0L, 5.7L (Replaces 99370A2)
This exhaust water shutter is a direct-fit replacement for MerCruiser V6 and V8 engines (4.3L, 5.0L, 5.7L) manufactured between 1982 and 1987, specifically for models equipped with a 3" Y-Pipe exhaust system. It acts as a critical check valve, preventing water from flowing back into the engine via the exhaust system.
This part directly replaces MerCruiser 99370A2, Sierra 18-2733, Mallory Marine 9-42801, GLM 89160, and Marine Pro 69370P.
- Installation Type: Direct replacement in Y-pipe assembly
- Material: Durable rubber with metal mounting hardware
- Function: Prevents water reversion to protect the engine
Compatible Engine Models
Confirm your engine model/year in the table below.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| MerCruiser | V6 4.3L | 185 HP | 4-Stroke | 1983-1986 | 99370A2 | 2 BBL |
| MerCruiser | V6 4.3L | 205 HP | 4-Stroke | 1985-1986 | 99370A2 | 4 BBL |
| MerCruiser | V8 5.0L | 200 HP | 4-Stroke | 1982-1987 | 99370A2 | 2 BBL, 305 CID |
| MerCruiser | V8 5.0L | 228 HP | 4-Stroke | 1982-1987 | 99370A2 | 4 BBL, 305 CID |
| MerCruiser | V8 5.0L | 230 HP | 4-Stroke | 1982-1987 | 99370A2 | 4 BBL, 305 CID |
| MerCruiser | V8 5.0L | 898 | 4-Stroke | 1982-1987 | 99370A2 | 2 BBL, 305 CID |
| MerCruiser | V8 5.7L | 260 HP | 4-Stroke | 1982-1987 | 99370A2 | 4 BBL, 350 CID |
Technical Specifications
| Specification | Value |
| Product Type | Exhaust Water Shutter/Flapper |
| Installation | Direct replacement in Y-pipe assembly |
| Fuel Type | Gasoline |
| Housing Material | Rubber with metal mounting hardware |
| Dimensions | Approximately 3" (76.2 mm) diameter |
| Other Technical Attributes | Acts as a flexible check valve to prevent water from returning up the exhaust system to the engine |
Package Contents
- 1 x Exhaust Water Shutter (Replaces 99370A2)
Installation Guide
- Ensure the engine is off, cool to the touch, and disconnect the battery for safety.
- Locate the Y-pipe exhaust assembly where the original water shutter is housed.
- Carefully remove the old, worn, or damaged shutter. This may involve removing clamps or other hardware.
- Thoroughly clean the interior surfaces of the Y-pipe where the new shutter will be seated.
- Position the new water shutter correctly, ensuring the flapper can move freely in the intended direction.
- Secure the shutter in place using the original or new mounting hardware.
- Reconnect any exhaust components that were removed.
- Reconnect the battery.
- Start the engine and check for any exhaust leaks or unusual noises at idle.
Troubleshooting & FAQ
How do I know if this water shutter will fit my engine?
This shutter is specifically designed for MerCruiser V6/V8 engines (4.3L, 5.0L, 5.7L) from 1982–1987 that use a 3" Y-Pipe. Please review the detailed compatibility table on this page and verify that your engine's original part number is listed as a direct replacement, such as 99370A2.
What are the signs of a failing exhaust water shutter?
Common symptoms include a distinct rattling noise from the exhaust, especially at idle; water ingestion back into the engine (which can cause hydrolock); or unexplained overheating issues. A visual inspection during maintenance may reveal a torn, melted, or completely missing flapper.
How often should I replace the exhaust water shutter?
Replacement frequency depends on factors like engine hours, operating conditions (saltwater vs. freshwater), and storage. We recommend a visual inspection at least once a year during routine maintenance and immediate replacement if you notice any cracking, warping, or deterioration.
OEM vs. Aftermarket?
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.
How fast do you ship and how much does it cost?
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.
What is your warranty and return policy?
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.
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