Sierra 18-3066 Mercury/Mariner/Yamaha Impeller
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The Sierra 18-3066 is a six-blade replacement lower-unit water pump impeller for select Mercury, Mariner and Yamaha outboards. It installs inside the gearcase water pump and circulates cooling water through the engine. The 47-3066 number is a distributor SKU for Sierra part 18-3066, which replaces Mercury/Mariner 47-11590M and Yamaha 6G1-44352-00-00.
Key Features
- Sierra manufacturer part number: 18-3066
- Distributor SKU: 47-3066
- Six flexible neoprene impeller blades
- Approximately 1-9/16-inch outside diameter
- Approximately 11/16- to 3/4-inch depth
- Approximately 0.470-inch shaft bore
- Designed for select Mercury, Mariner and Yamaha 6–8 HP outboards
- Included in Sierra water pump kit 18-3460
- UPC: 030999315182
Engine Compatibility
Documented Yamaha applications include:
- Yamaha 6 HP two-stroke: approximately 1986–2000
- Yamaha 8 HP two-stroke: approximately 1984–2009
Documented Mercury and Mariner applications include select 6C, 6D and 8C two-stroke outboards using OEM impeller 47-11590M. Exact compatibility depends on the complete model, production year, serial number and gearcase configuration.
Serial Number Fitment Notice
Do not select this impeller by horsepower alone. Mercury, Mariner and Yamaha used different water pump assemblies across similar small-outboard families.
Before ordering, confirm:
- Complete engine model and serial number
- Production year
- Gearcase and water pump assembly
- Original impeller number
- Mercury/Mariner reference 47-11590M
- Yamaha reference 6G1-44352-00-00
- Impeller diameter, depth and shaft bore
- Drive-key configuration
The original water pump parts diagram provides the most reliable fitment confirmation.
When This Part Needs Replacement
Replace the impeller if:
- Cooling-water discharge becomes weak or intermittent
- The engine begins operating hotter than normal
- The blades are cracked, torn, stiff or permanently bent
- Rubber fragments are missing
- The centre hub slips inside the impeller
- The engine has been operated without cooling water
- The motor has operated in sandy or silty conditions
- The scheduled water pump service interval has been reached
Dry operation, sand and silt can quickly damage the flexible impeller blades and reduce cooling-water delivery.
Installation Notes
Lower-unit removal is normally required to access the water pump assembly. During service:
- Disconnect the ignition and battery where applicable
- Follow the correct shift-linkage and lower-unit removal procedure
- Inspect the pump housing, cup, wear plate, key, seals and driveshaft
- Remove broken impeller fragments from the pump and cooling passages
- Lubricate the new impeller with clean soapy water or an approved assembly lubricant
- Position the drive key correctly
- Rotate the driveshaft in its normal operating direction while lowering the housing over the blades
- Replace worn gaskets, O-rings and pump components
- Reinstall the lower unit according to the engine service manual
- Confirm strong cooling-water flow before operating under load
Never operate the outboard without an adequate cooling-water supply.
Alternate/Superseded Part Numbers
- Sierra: 18-3066
- Distributor SKU: 47-3066
- Sierra catalogue reference: 118-3066
- Mercury/Mariner: 47-11590M
- Mercury shortened reference: 11590M
- Yamaha: 6G1-44352-00-00
- Yamaha shortened reference: 6G1-44352-00
- GLM Marine: 89870
- Mallory Marine: 9-45610
- CEF: 500302
- UPC: 030999315182
Parts Desk Insight
The 47-3066 number resembles a Mercury OEM number, but it is the distributor SKU for Sierra 18-3066. Match the engine's original impeller to Mercury 47-11590M or Yamaha 6G1-44352-00-00 rather than ordering from horsepower alone.
Compatible & Related Products
Other impellers and water pump kits for small Mercury/Mariner and Yamaha outboards available at Marisol Marine:
Shipping information
In-stock and OEM parts: ship same or next business day.
Locally warehoused items: ship within 3–4 business days.
Special-order items: timeline confirmed after order.
Returns & warranty
Returns & Satisfaction Guarantee
We stand firmly behind the quality of every product we sell. Your confidence matters to us — and we back it with a straightforward 30-Day Satisfaction Guarantee.
If you are not fully satisfied, you may request a return within 30 days of delivery. All returns must receive pre-approval prior to being sent back. Unauthorized returns will not be accepted.
To qualify for a return:
Item must be in new, unused condition
Product must be in its original packaging
All parts, components, hardware, manuals, and accessories must be included
Packaging must be undamaged and suitable for resale
Important:
Electronics are strictly inspected. No returns on open-box electronics. Exceptions may apply only with prior written approval. Any electronic unit that has been installed, powered, activated, or altered may not be eligible for return.
We are serious about product integrity — and equally serious about taking care of our customers. If there is ever a product issue, contact us immediately so we can make it right.
For return authorization, please contact our support team before shipping anything back.