Exhaust Water Shutter/Flapper – Fits MerCruiser V6 & V8 Engines 1982–1987 (Replaces 99370A2, 23-92852, 92802, 18-2733, 89160, 9-42801)
Exhaust Water Shutter/Flapper – Fits MerCruiser V6 & V8 Engines 1982–1987 (Replaces 99370A2, 23-92852, 92802, 18-2733, 89160, 9-42801) is backordered and will ship as soon as it is back in stock.
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Delivery and Shipping
Delivery and Shipping
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Exhaust Water Shutter/Flapper – Fits MerCruiser V6 & V8 Engines...
Product Details
This Exhaust Water Shutter/Flapper is designed to prevent water from flowing back into the engine through the exhaust system. It is engineered for MerCruiser V6 (4.3L) and V8 (5.0L, 5.7L) stern drive engines produced between 1982 and 1987 that are equipped with 3-inch exhaust Y-pipes.
This part serves as a direct replacement for multiple OEM and aftermarket part numbers, including Mercury 99370A2 and Sierra 18-2733.
- Acts as a flexible check valve to block water reversion.
- Installs directly into the exhaust Y-pipe using the included grommets.
- Constructed from durable rubber with a steel rod core for longevity.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Mercury | 99370A2 |
| Mercury | 92802 |
| Mercury Quicksilver | 23-92852 |
| Sierra | 18-2733 |
| GLM | 89160 |
| Mallory | 9-42801 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
For MerCruiser applications, verify that your engine falls within the specified model years and uses a 3-inch exhaust Y-pipe, as this component is size-specific.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| MerCruiser | V6 (4.3L) Stern Drive | Various | 4-Stroke | 1982–1987 | 99370A2 | For engines with 3-inch Y-pipes |
| MerCruiser | V8 (5.0L, 5.7L) Stern Drive | Various | 4-Stroke | 1982–1987 | 99370A2 | For engines with 3-inch Y-pipes |
Technical Specs
- Product Type
- Exhaust Water Shutter/Flapper
- Installation
- Exhaust Y-pipe (3-inch)
- Connection
- Fits into 3-inch Y-pipes
- Housing Material
- Rubber with steel rod core
- Housing Color
- Black
- Dimensions
- Approximately 3 inches (76.2 mm) width
- Fitting Type
- Drop-in with retainer grommets
- Warranty
- Varies by manufacturer (typically 1 year)
- Other Technical Attributes
- Acts as a flexible check valve to prevent water backflow into engine
What’s in the Box
- 1 x Water Shutter Flapper Kit (99370A2)
- 2 x Retainer Grommets
Installation Notes
- Gain access to the exhaust Y-pipe where it connects to the transom assembly. This may require removing the sterndrive unit and/or exhaust elbows.
- Carefully remove the old, worn, or damaged water shutter and its retainer grommets.
- Clean the inside surfaces of the Y-pipe to ensure a proper seal and fit for the new shutter.
- Insert the new water shutter into the designated slot in the Y-pipe.
- Secure the shutter by pressing the new retainer grommets into the holes on each side of the Y-pipe, ensuring they hold the shutter's core rod in place.
- Reassemble the exhaust components and sterndrive unit, tightening all hardware to manufacturer specifications.
Troubleshooting & FAQ
How do I know if this water shutter fits my engine?
Confirm that your engine is a MerCruiser V6 or V8 model from 1982–1987. Most importantly, you must verify that your engine is equipped with a 3-inch inner diameter exhaust Y-pipe, as this part is size-specific.
What are the signs of a failing water shutter?
Common symptoms include a rattling noise from the exhaust at idle, engine hesitation or stalling when coming off plane, and in severe cases, water ingestion leading to hydrostatic lock. Damaged shutters may break apart, causing blockages downstream.
How often should I replace my exhaust shutters?
It is recommended to inspect and replace water shutters during routine exhaust system service, such as when replacing manifolds and risers. They are wear items and should be checked every few years, especially in saltwater environments.
Is this the same as the "lower" shutter used in some V8 models?
No, this is the upper water shutter located in the 3-inch Y-pipe. Some V8 models use an additional, larger shutter further down the exhaust path which is a different part number.
Why are the two small grommets included?
The two retainer grommets are essential for installation. They are inserted into the holes on the sides of the Y-pipe to secure the steel rod of the shutter, allowing it to pivot correctly while holding it in place.
OEM vs. Aftermarket?
This listing is an aftermarket replacement (not OEM). Built to OEM-level specifications with comparable materials. Manufactured in an ISO 9002 facility, batch-inspected for consistency.
Shipping speed & cost
We ship worldwide quickly—typical transit 5–15 days. Standard shipping is free; expedited options appear at checkout where available.
Warranty & returns
Covered by a 1-year warranty against manufacturing defects under normal use. If issues arise, contact support with your order details. Returns are accepted within our standard window (unused & in original condition). See our policy page or reach out for instructions.
Safety & Important Info
- Verify images/specifications vs your original part. If anything differs—even if your model appears compatible—do not purchase.
- This is an aftermarket replacement, not an OEM component.
- Professional installation is recommended for safety and performance.
About Sea Sierra
- Pro-Grade Standards — We supply marine parts engineered to OEM-level tolerances and tested for real-world conditions.
- Fast Global Fulfillment — Free standard delivery to most regions in 5–15 days.
- Manufacturer-Direct Value — Fair pricing without compromising on materials or QC.
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