Water Pump Impeller – Fits Tohatsu/Nissan 9.9–20 HP & Mercury 8–20 HP (Replaces 334-65021-0, 47-803748)

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Water Pump Impeller – Fits Tohatsu/Nissan 9.9–20 HP & Mercury 8–20 HP (Replaces 334-65021-0, 47-803748) 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 Water Pump Impeller – Fits Tohatsu/Nissan 9.9–20 HP & Mercury 8–20 HP (Replaces 334-65021-0, 47-803748) is a critical component for maintaining your engine's cooling system. It is designed for Tohatsu/Nissan 9.9-20 HP (2-Stroke & 4-Stroke), Mercury/Mariner 8-20 HP (4-Stroke), and is cross-compatible with select Honda 7.5-10 HP outboard motors.

This part provides a direct interchange for OEM part numbers Tohatsu 334-65021-0, Mercury 47-803748/8M0214944, Honda 19210-935-003, Evinrude 5040046, and Sierra 18-8921.

Installs as a direct OEM-equivalent replacement.
Features a key-driven shaft mount for secure fitting.
Made from salt water resistant rubber for durability in marine environments.

Part Number Matrix

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

Brand	Part Number
Tohatsu/Nissan	334-65021-0 / 334650210 / 334650210M
Mercury	47-803748 / 8M0214944
Honda	19210-935-003
Evinrude	5040046
Sierra	18-8921

Engine & Model Compatibility

Confirm your engine model/year in the table below.

Fits a range of Tohatsu & Nissan 2-stroke and 4-stroke outboard models from 9.9 HP to 20 HP.

Designed for Mercury & Mariner 4-stroke outboards from 8 HP to 20 HP, including Bigfoot gearcase models.

Cross-compatible with specific Honda and Evinrude models as listed.

Brand	Model	Rated HP	Stroke	OEM Part No.	Notes
Tohatsu	MFS9.9/15/18/20	9.9-20	4-Stroke	334-65021-0
Nissan	NSF9.9/15/18/20	9.9-20	4-Stroke	334-65021-0
Tohatsu	M9.9/15/18/20	9.9-20	2-Stroke	334-65021-0
Nissan	NS9.9/15/18/20	9.9-20	2-Stroke	334-65021-0
Mercury	F8/F9.9/F10/F15/F18/F20	8-20	4-Stroke	47-803748	Also fits Bigfoot gearcase models
Mercury Marine	8M0135803	9.9-20	4-Stroke	8M0214944	Service kit part number
Honda	BF7.5/BF10	7.5-10	4-Stroke	19210-935-003	Cross-compatible
Evinrude	E15	15		5040046	Cross-compatible

Technical Specs

Product Type: Water Pump Impeller
Installation: Direct OEM Replacement
Connection: Key-driven Shaft Mount
Housing Material: High-quality Rubber
Housing Color: Black
Fitting Type: Shaft Mount with Key
Other Technical Attributes: Salt water resistant

What’s in the Box

1 x Water Pump Impeller (334-65021-0/47-803748)

Installation Notes

Disconnect the spark plug wires and battery cables for safety.
Place a drain pan under the gearcase and remove the drain plug to empty the gear oil.
Unbolt and carefully lower the gearcase (lower unit) from the outboard's main housing.
Locate the water pump housing on top of the gearcase and remove its retaining bolts.
Slide the housing up and off the driveshaft to expose the old impeller. Note the orientation of the vanes.
Remove the old impeller and key. Clean any debris or corrosion from the housing and wear plate.
Install the new key and slide the new impeller onto the driveshaft. Rotate the shaft clockwise while pushing down to seat the vanes correctly.
Apply a light coat of marine grease to the inside of the housing and reinstall it.
Re-bolt the water pump housing to the specified torque.
Reattach the gearcase to the outboard, ensuring the driveshaft, shift shaft, and water tube align correctly.
Refill the gearcase with new lubricant and start the engine in water to verify proper water flow from the tell-tale outlet.

Troubleshooting & FAQ

How do I know when to replace my water pump impeller?

Signs of a failing impeller include a weak or intermittent water stream from the "tell-tale" outlet, engine overheating alarms, or a noticeable drop in cooling performance. It's recommended to replace it as part of regular annual service, or every 100-200 hours of use, whichever comes first.

What are the symptoms of complete impeller failure?

Complete failure will result in a total loss of cooling water flow, leading to rapid engine overheating, which can cause severe and permanent damage. You will likely get an overheat warning on your console or engine management system.

Is this impeller compatible with both 2-stroke and 4-stroke engines?

Yes, as specified in the compatibility table, this impeller fits a range of both 2-stroke and 4-stroke models from Tohatsu and Nissan, and 4-stroke models from Mercury/Mariner and Honda.

Can I install this myself?

While DIY installation is possible for those with mechanical experience, it involves removing the lower unit of your outboard. We recommend professional installation to ensure correct seating of the impeller, proper alignment of shafts, and to prevent damage to the engine.

My engine model is listed, but the year is not. Will it fit?

This part is listed by engine model and horsepower range. While specific year ranges are not provided, it is designed to fit the models listed. Always compare the photos and part numbers to your existing impeller to be certain. When in doubt, consult a professional mechanic.

What is the difference between this and an OEM impeller?

This is an aftermarket replacement part, not an original equipment manufacturer (OEM) component. It is engineered to meet or exceed OEM specifications for fit, form, and function, using high-quality, salt-water resistant rubber for reliable performance.

How fast is shipping, and what is the cost?

We ship worldwide quickly—typical transit is 5–15 days. Standard shipping is free; expedited options will appear at checkout where available for your location.

What is the warranty and return policy?

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

Safety & Important Info

Verify images and specifications against your original part before purchase. 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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