Water Pump Impeller – Fits Mercury/Tohatsu 8-20 HP 4-Stroke Outboards (Replaces 47-803748)

$21.50 $34.00

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Water Pump Impeller – Fits Mercury/Tohatsu 8-20 HP 4-Stroke Outboards (Replaces 47-803748) is backordered and will ship as soon as it is back in stock.

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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 aftermarket Water Pump Impeller – Fits Mercury/Tohatsu 8-20 HP 4-Stroke Outboards is engineered for a wide range of applications, including Mercury/Tohatsu 8–20 HP 4-Stroke (2003 and newer), Command Thrust models, 209cc Mercury engines, and select Honda 7.5–10 HP 4-Stroke outboards.

It provides a direct interchange for numerous OEM and aftermarket part numbers from leading brands like Mercury, Tohatsu, Honda, and more.

Installs directly using the included key and existing keyway.
Constructed from high-durability neoprene rubber with a hardened nylon insert for longevity.
Kit includes one impeller and one impeller key for a complete replacement.

Part Number Matrix

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

Brand	Part Number
Mercury	47-803748
Mercury	8M0135803
Mercury	8M0214944
Tohatsu	334-65021-0
Tohatsu	334650210M
Honda	19210-935-003
Evinrude/Johnson	5040046
Sierra	18-8921
CEF Marine	500383

Engine & Model Compatibility

Confirm your engine model/year in the table below.

Provides coverage for many Mercury/Mariner 4-stroke models from 8 to 20 HP, including Command Thrust and international variants.

Brand	Model	Rated HP	Stroke	Years	OEM Part No.	Notes
Mercury	8 HP Command Thrust	8	4-Stroke	2003+	47-803748	209cc models
Mercury	9.9 HP Command Thrust	9.9	4-Stroke	2003+	47-803748	209cc models
Mercury	9.9 HP International	9.9	4-Stroke		47-803748	2 cylinder models
Mercury	10 HP	10	4-Stroke		47-803748
Mercury	15 HP	15	4-Stroke	2003+	47-803748
Mercury	15 HP Super International	15	4-Stroke		47-803748
Mercury	18 HP	18	4-Stroke		47-803748
Mercury	20 HP	20	4-Stroke		47-803748

Fits a wide range of Tohatsu and Nissan 2-stroke and 4-stroke outboards from 9.9 to 20 HP.

Brand	Model	Rated HP	Stroke	OEM Part No.
Tohatsu	M9.9, NS9.9	9.9	2-Stroke	334-65021-0
Tohatsu	M15, NS15	15	2-Stroke	334-65021-0
Tohatsu	M18, NS18	18	2-Stroke	334-65021-0
Tohatsu	MFS9.9, NSF9.9C	9.9	4-Stroke	334-65021-0
Tohatsu	MFS15, NSF15	15	4-Stroke	334-65021-0
Tohatsu	MFS18, NSF18	18	4-Stroke	334-65021-0
Tohatsu	MFS20, NSF20	20	4-Stroke	334-65021-0

Applicable to some Honda 4-stroke models, primarily in the 7.5 to 10 HP range.

Brand	Model	Rated HP	Stroke	OEM Part No.	Notes
Honda	BF75, BF75Z, BF75K1-K3	7.5	4-Stroke	19210-935-003
Honda	BF100, BF100Z	10	4-Stroke	19210-935-003
Honda	BF75Z	75	4-Stroke	19210-935-003	Less common application
Honda	BF100Z	100	4-Stroke	19210-935-003	Less common application

Listed as compatible with select Evinrude/Johnson 15 HP applications.

Brand	Model	Rated HP	OEM Part No.	Notes
Evinrude	Various	15	5040046

Technical Specs

Product Type: Water Pump Impeller
Material: Neoprene rubber with hardened nylon insert
Number of Blades: 8
Height: 23.8 mm (0.94 in)
Diameter: 41.2 mm (1.62 in)
Hub Diameter: 14.0 mm (0.55 in)
Weight: 0.70 oz (19.8 g)
Color: Black
Installation Type: Keyway
Warranty: 1 Year (aftermarket)

What’s in the Box

1 x Water Pump Impeller (47-803748)
1 x Impeller Key (28-803749)

Installation Notes

Disconnect the battery and remove the engine cover.
Place the outboard in neutral and drain the lower unit gear oil.
Remove the bolts securing the lower unit to the engine.
Carefully separate the lower unit, taking note of the shift shaft linkage.
Unbolt and remove the water pump housing cover.
Slide the old impeller off the driveshaft, removing the old key.
Clean the housing and base plate, inspecting for wear or damage.
Insert the new impeller key into the driveshaft keyway.
Align the new impeller with the key and slide it onto the shaft.
Reinstall the housing, ensuring the blades are oriented correctly (turn the shaft clockwise).
Reassemble the lower unit in the reverse order of removal.
Refill the gear oil and test the engine with a water supply.

Troubleshooting & FAQ

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

The best way is to cross-reference your existing part number with our Part Number Matrix. Additionally, check our Engine & Model Compatibility tables. If your model or part number is not listed, this part may not fit.

What are common signs of a worn or failed impeller?

A weak or no water stream from the "tell-tale" port, engine overheating alarms, or a noticeable decrease in engine cooling performance are all indicators that the impeller may need inspection or replacement.

How often should a water pump impeller be replaced?

As a preventative maintenance item, it is recommended to replace the impeller every 1-2 years or every 100-200 hours of operation, whichever comes first. This interval can be shorter in saltwater or silty/sandy conditions.

Why is the included impeller key important?

The key is a small but critical component that locks the impeller to the driveshaft, ensuring it spins correctly to pump water. Always use a new key during installation, as the old one may be worn or fatigued.

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

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Fast Global Fulfillment — Free standard delivery to most regions in 5–15 days.
Manufacturer-Direct Value — Fair pricing without compromising on materials or QC.

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