Exhaust Water Shutter Kit – Fits MerCruiser 3.0-4.2L (Replaces Mercury/MerCruiser 807166A3, Sierra 18-2732-9)
Exhaust Water Shutter Kit – Fits MerCruiser 3.0-4.2L (Replaces Mercury/MerCruiser 807166A3, Sierra 18-2732-9) is backordered and will ship as soon as it is back in stock.
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Worry-free returns
Worry-free returns
You may return most new, unopened items within 7 days of delivery for a full refund. We'll also pay the return shipping costs if the return is a result of our error (you received an incorrect or defective item, etc.).
You should expect to receive your refund within four weeks of giving your package to the return shipper, however, in many cases you will receive a refund more quickly. This time period includes the transit time for us to receive your return from the shipper (5 to 10 business days), the time it takes us to process your return once we receive it (3 to 5 business days), and the time it takes your bank to process our refund request (5 to 10 business days).
If you need to return an item, simply login to your account, view the order using the "Complete Orders" link under the My Account menu and click the Return Item(s) button. We'll notify you via e-mail of your refund once we've received and processed the returned item.
Delivery and Shipping
Delivery and Shipping
Free standard shipping on all orders under 1 KG
Exhaust Water Shutter Kit – Fits MerCruiser 3.0-4.2L (Replaces Merc...
Product Details
This Exhaust Water Shutter Kit is designed for MerCruiser 3.0L, 3.6L, and 4.2L inboard and sterndrive engines from model years 1994–1997. It functions as a flexible check valve, preventing water from flowing back up the exhaust system and into the engine.
This kit is a direct interchange for several part numbers, including Mercury/MerCruiser 807166A3, Sierra 18-2732-9, GLM 89170, and Mallory 9-42802.
- Designed for direct replacement, ensuring a secure fit.
- Made from durable rubber/elastomer material to withstand the marine environment.
- Kit includes two water shutters to complete the job.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number |
|---|---|
| Mercury/MerCruiser | 807166A3 |
| Sierra | 18-2732-9 |
| GLM | 89170 |
| Mallory | 9-42802 |
Engine & Model Compatibility
Confirm your engine model/year in the table below.
For MerCruiser Engines: This part fits specific serial number ranges. Please verify your engine's serial number against the notes provided in the table to ensure correct fitment.
| Brand | Model | Rated HP | Stroke | Years | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| MerCruiser | D3.0L (BRAVO) VM 183 I/L5 Sterndrive | 135 | 4-Stroke | 1994–1997 | 807166A3 | Serial: 0D725152 THRU 0F999999 |
| MerCruiser | D3.0L VM 183 I/L5 Inboard/TowSports | 135 | 4-Stroke | 1994–1995 | 807166A3 | Serial: 0D725152 THRU 0F999999 |
| MerCruiser | D3.6L VM 219 I/L6 Inboard/TowSports | 4-Stroke | 807166A3 | Serial: 0D850128 THRU 99999999999999999 | ||
| MerCruiser | D3.6L (BRAVO) VM 219 I/L6 Sterndrive | 4-Stroke | 807166A3 | Serial: 0D850128 THRU 99999999999999999 | ||
| MerCruiser | D4.2L/220 IDI VM 254 I/L6 Sterndrive | 220 | 4-Stroke | 807166A3 | Serial: 0D554732 THRU 0M999999 | |
| MerCruiser | D4.2L/220 IDI VM 254 I/L6 Inboard/TowSports | 220 | 4-Stroke | 807166A3 | Serial: 0D554732 THRU 0M999999 |
Technical Specs
- Product Type
- Exhaust Water Shutter Kit
- Also Known As
- Water flapper
- Installation
- Direct replacement
- Function
- Acts as a flexible check valve to stop water from returning up the exhaust system to the engine
- Material
- Rubber/Elastomer
- Dimensions
- 2.5 in (63.5 mm)
- Package Quantity
- 2 water shutters
What’s in the Box
- 2 x Water Shutters (Replaces 807166A3)
Installation Notes
- Ensure the engine is completely cool and disconnect the battery for safety.
- Locate the exhaust Y-pipe where it meets the riser or manifold.
- Loosen clamps and remove the attached exhaust hoses to access the old water shutter housing.
- Carefully remove the old, worn shutters from inside the exhaust pipe.
- Thoroughly clean the sealing surfaces, removing any old gasket material or debris.
- Insert the new water shutters, ensuring they are oriented correctly with the hinge at the top to allow exhaust out while blocking returning water.
- Reconnect all hoses and securely tighten the clamps to prevent any leaks.
- Reconnect the battery, start the engine, and meticulously check for water or exhaust leaks around the service area.
Troubleshooting & FAQ
How do I know if my exhaust shutters need replacing?
Common signs of failure include engine overheating at idle, difficulty starting, a rattling noise from the exhaust, or water ingestion into the engine cylinders (a serious condition). Visual inspection showing cracked, brittle, or missing flaps also indicates a replacement is needed.
What is the function of an exhaust water shutter?
It's a one-way valve in your exhaust system that lets exhaust gases out but closes to prevent water from surging back up the pipe and into the engine when you decelerate or are in rough seas. They are also known as "water flappers."
Can I run my engine without water shutters?
It is strongly discouraged. Running without them exposes your engine to the risk of catastrophic water ingestion and subsequent hydrostatic lock, which can cause severe internal engine damage.
Is there a specific orientation for installation?
Yes. The shutters must be installed so the flaps can swing open with exhaust pressure but close against water backflow. Typically, the hinge is at the top. Incorrect installation will not protect the engine.
How often should I inspect or replace my exhaust shutters?
We recommend inspecting them annually or every 100 hours of operation. They are a critical wear item and should be replaced as part of preventative maintenance, especially on boats operated in saltwater.
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.
Payment & Security
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