Water Pump Impeller – Fits Mercury/Mariner 8/9.9 HP 4-Stroke, 6/8/9.8 HP 2-Stroke (Replaces 47-8037481, 3B2-65021-1)

$13.69 $21.00

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Water Pump Impeller – Fits Mercury/Mariner 8/9.9 HP 4-Stroke, 6/8/9.8 HP 2-Stroke (Replaces 47-8037481, 3B2-65021-1) is backordered and will ship as soon as it is back in stock.

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

Free standard shipping on all orders under 1 KG

If you have any questions, feel free to email us at info@sierramarines.com, and we’ll get back to you within 20–36 hours.

Product Details

This high-quality Water Pump Impeller – Fits Mercury/Mariner 8/9.9 HP 4-Stroke, 6/8/9.8 HP 2-Stroke (Replaces 47-8037481) is an essential replacement component for maintaining your outboard engine’s cooling system. It is designed for a broad range of Mercury/Mariner (8–9.9 HP 4-Stroke, 6–9.8 HP 2-Stroke), Tohatsu/Nissan (6–9.8 HP 2-Stroke, 8–9.8 HP 4-Stroke), and Parsun (6–9.8 HP) models, ensuring reliable water circulation to prevent overheating.

This component serves as a direct replacement for Mercury 47-8037481, 8M0214945; Tohatsu 3B2-65021-1; Sierra 18-8920; CEF 500344; Mallory 9-45401; and Parsun PAF8-04000200.

Installs as a direct-fit component within the lower unit water pump assembly.
Constructed from durable neoprene rubber with a plastic hub for longevity in marine environments.
Kit includes the impeller and a square drive key required for driveshaft mounting.

Part Number Matrix

Use this matrix to confirm equivalent references across OEM and aftermarket brands.

Brand	Part Number
Mercury / Mariner	47-8037481, 8037481, 8M0214945
Tohatsu / Nissan	3B2-65021-1, 3B2650211
Sierra	18-8920
CEF	500344
Mallory	9-45401
Parsun	PAF8-04000200

Engine & Model Compatibility

Confirm your engine model and year in the table below to ensure accurate fitment.

For Mercury/Mariner owners: This impeller fits specific 8/9.9 HP 4-stroke models (2005 and newer, non-BigFoot) and various international 2-stroke SeaPro models. Please check your serial number range (0P325500 and up for the 4-strokes).

For Tohatsu/Nissan owners: Compatible with a wide range of 6, 8, and 9.8 HP models in both 2-stroke and 4-stroke configurations, including the MFS8 and MFS9.8 series.

For Parsun owners: Fits corresponding F6, F8, and F9.8 aftermarket engine models.

Brand	Model	Rated HP	Stroke	Years	OEM Part No.	Notes
Mercury	8/9.9 (209cc)	8/9.9	4-Stroke	2005+ (0P325500+)	47-8037481	Non-BigFoot models
Mercury	8/9.8 SeaPro	8/9.8	2-Stroke	Various	47-8037481	2 cylinder (International) models
Mercury	6/8	6/8	2-Stroke	Various	47-8037481	2 cylinder (International) models
Tohatsu	Various	6/8/9.8	2-Stroke	Various	3B2-65021-1	All compatible models
Tohatsu	MFS8/MFS9.8	8/9.8	4-Stroke	Various	3B2-65021-1	All compatible models
Nissan	Various	6/8/9.8	2-Stroke	Various	3B2-65021-1	Models sharing same design with Tohatsu
Parsun	F6/F8/F9.8	6/8/9.8		Various	PAF8-04000200	Aftermarket fit

Technical Specs

Product Type: Water Pump Impeller
Installation: Replaceable component in lower unit water pump assembly
Material: Neoprene rubber with plastic hub
Number of Blades: 6
Outer Diameter: 40.00 mm (1.587 inches)
Hub Diameter: 18.00 mm (0.709 inches)
Inner Shaft Diameter: 11.58 mm (0.472 inches)
Key Type: Square key required for installation
Rotation: Clockwise
Operating Temperature: -10°C to 80°C (14°F to 176°F)
Warranty: 1 Year (varies by supplier)

What’s in the Box

1 x Water Pump Impeller (47-8037481 / 3B2-65021-1)
1 x Square Drive Key (for driveshaft mounting)

Installation Notes

Disconnect the negative battery cable to prevent accidental starting.
Place a drain pan under the lower unit and remove the gear oil drain/fill screws to empty the gearcase.
Remove the bolts securing the lower unit (gearcase) to the engine's mid-section and carefully slide it off.
Unscrew the bolts on the water pump housing cover to access the impeller.
Remove the old impeller from the driveshaft, taking note of the drive key's orientation. Remove the old key.
Clean any debris or corrosion from the impeller housing and wear plate. Inspect them for deep grooves or warping and replace if necessary.
Insert the new drive key into the driveshaft slot.
Lightly coat the new impeller and the inside of the housing with marine grease. Slide the new impeller onto the shaft while turning the driveshaft clockwise to correctly fold the blades.
Reinstall the water pump housing and torque the bolts to manufacturer specifications.
Re-attach the lower unit to the engine, ensuring the driveshaft, shift shaft, and water tube are correctly aligned.
Refill the lower unit with fresh marine gear oil until it seeps from the upper vent hole, then reinstall both screws.
Reconnect the battery. Before launching, test the engine with a water source ("muffs") to confirm a strong, steady stream from the tell-tale outlet.

Troubleshooting & FAQ

How do I confirm this impeller fits my exact engine model?

The most reliable method is to match your engine's model, year, and serial number against the compatibility table. For Mercury models, the serial number (e.g., 0P325500+) is crucial. If your old part number matches one listed in our Part Number Matrix, it is also a strong indicator of a correct fit.

What are the signs of a failing water pump impeller?

Common symptoms include a weak or non-existent water stream from the "tell-tale" outlet, engine overheating alarms, or a noticeable decrease in engine performance. Impellers can become brittle, cracked, or lose blades over time, reducing their ability to pump water effectively.

How often should I replace my impeller?

As a general rule, it is recommended to inspect your impeller annually and replace it every 1-2 years or every 100-200 hours of use, whichever comes first. Usage in saltwater or sandy/murky water may require more frequent replacement.

Is the square drive key included with the impeller?

Yes, this kit includes one water pump impeller and one square drive key for mounting on the driveshaft. Please check the "What's in the Box" section for a complete list of contents.

My engine still overheats after installing the new impeller. What could be wrong?

First, ensure the impeller blades were oriented correctly (usually by turning the driveshaft clockwise during installation). Other potential causes include a clogged water intake, a blocked cooling passage somewhere else in the engine, a worn or damaged water pump housing, or a faulty thermostat. A thorough system flush may be necessary.

What is the difference between an OEM and an aftermarket part?

This listing is an aftermarket replacement (not OEM). It is built to OEM-level specifications with comparable materials. All parts are manufactured in an ISO 9002 certified facility and are batch-inspected to ensure quality and consistency.

How fast is shipping and what does it cost?

We ship worldwide quickly—typical transit is 5–15 days. Standard shipping is free to most regions, with expedited options available at checkout where applicable.

What is the warranty and return policy?

This product is covered by a 1-year warranty against manufacturing defects under normal use. If you encounter any issues, please contact our support team with your order details. Returns are accepted within our standard window for items that are unused and in their original condition. See our full 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 quality control.

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