The Sierra 18-3001 is a six-blade replacement water pump impeller for select vintage Johnson, Evinrude and OMC outboards. It installs inside the lower-unit water pump housing and circulates cooling water through the engine. This impeller is intended for metal water pump housings and replaces OEM numbers 277181 and 434424. Applications using a plastic pump housing require a different impeller.
Key Features
- Sierra manufacturer part number: 18-3001
- Six flexible impeller blades
- Outside diameter: approximately 2.75 inches
- Thickness: approximately 0.50 inch
- Shaft bore: approximately 0.43 inch
- Key slot: approximately 0.145 inch
- Designed for metal water pump housings
- Drive key is not included
- Replaces Johnson/Evinrude/OMC 277181 and 434424
- UPC: 030999237118
Engine Compatibility
Documented applications include select Johnson and Evinrude outboards:
- 3 HP: 19521978
- 4 HP: 19691972
- 4 HP: 19731983 when equipped with a one-water-tube pump
- 5 HP: 19651968
- 5.5 HP: 19541964
- 6 HP: 19521978
- 7.5 HP: 19541958
Exact compatibility depends on the complete engine model number and the type of water pump housing installed.
Serial Number Fitment Notice
Do not select this impeller by horsepower or approximate year alone. Older Johnson and Evinrude engines may use different water pumps within the same horsepower range.
Before ordering, confirm:
- Complete engine model number
- Production year
- Metal water pump housing
- One- or two-water-tube configuration where applicable
- OEM impeller number 277181 or 434424
- Impeller diameter, thickness and shaft bore
- Drive-key arrangement
For applications with a plastic water pump housing, verify the correct alternative impeller rather than using Sierra 18-3001.
When This Part Needs Replacement
Replace the impeller if:
- Cooling-water discharge becomes weak or intermittent
- The engine begins running hotter than normal
- The blades are cracked, torn, stiff or permanently bent
- Pieces are missing from the blades
- The rubber has developed a permanent set from storage
- The centre hub slips inside the impeller
- The engine has been operated without cooling water
- The water pump’s preventive-maintenance interval has been reached
Regular inspection is particularly important on older outboards that may be operated only seasonally.
Installation Notes
Lower-unit removal is normally required to access the water pump. During service:
- Disconnect the ignition and battery where applicable
- Follow the correct shift-linkage and lower-unit removal procedure
- Confirm that the pump uses a metal housing
- Inspect the housing, wear plate, key, water-tube grommet and seals
- Remove any broken impeller fragments from the cooling passages
- Reuse the existing key only if it is undamaged, or obtain the correct replacement separately
- Lubricate the new impeller with clean soapy water or approved assembly lubricant
- Position the key correctly
- Rotate the driveshaft in its normal operating direction while lowering the housing over the blades
- 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: 18-3001
- Sierra catalogue reference: 118-3001
- Johnson/Evinrude/OMC: 277181
- Johnson/Evinrude/OMC: 0277181
- Johnson/Evinrude/OMC: 434424
- Johnson/Evinrude/OMC: 0434424
- GLM Marine: 89580
- Mallory Marine: 9-45216
- Mallory Marine: 9-45216-10
- CEF: 500350
- UPC: 030999237118
Parts Desk Insight
The most important distinction with Sierra 18-3001 is the pump housing material. It is designed for the older metal-housing water pump. Confirming both OEM number 277181 or 434424 and the housing type prevents confusion with similar-looking impellers used in later plastic pump housings.
Compatible & Related Products
Other Sierra Johnson/Evinrude impellers available at Marisol Marine:
- Sierra 3002 Johnson/Evinrude Impeller
- Sierra 3043 Johnson/Evinrude Impeller
- Sierra 3083 Johnson/Evinrude Impeller
- Sierra 3090 Johnson/Evinrude Impeller
- Sierra 3050 Johnson/Evinrude Impeller
- Sierra 3051 Johnson/Evinrude Impeller
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