Water Pump Impeller Kit – Fits Mercury 9.9-20 HP 4-Stroke (Replaces 8M0135821, 8M0137849)

$51.99 $83.00

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Water Pump Impeller Kit – Fits Mercury 9.9-20 HP 4-Stroke (Replaces 8M0135821, 8M0137849) is backordered and will ship as soon as it is back in stock.

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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).

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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 Water Pump Impeller Kit – Fits Mercury 9.9-20 HP 4-Stroke (Replaces 8M0135821, 8M0137849) is designed for Mercury and Mariner 4-Stroke outboards (9.9, 10, 15, and 20 HP, 333cc 2-Cylinder models) from 2020 and newer with serial numbers 0R833820 and above, including ProKicker and SeaPro variants. It is also compatible with select Nissan and Tohatsu MFS 15-20 HP models featuring equivalent cooling systems.

This kit serves as a direct interchange for Mercury OEM part numbers 8M0135821, 8M0137849, 98-8M0135821, 46-8M0135821, 46-8M0137849, Quicksilver 8M0134484, and Mercury 46-8M0122064.

Engineered as a direct-fit replacement for specified OEM parts, ensuring seamless installation.
Constructed with a corrosion-resistant marine alloy housing for enhanced durability in saltwater and freshwater.
The impeller is designed for improved flexibility across a wide range of water temperatures.

Part Number Matrix

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

Brand	Part Number
Mercury	8M0135821
Mercury	8M0137849
Mercury	98-8M0135821
Mercury	46-8M0135821
Mercury	46-8M0137849
Mercury/Quicksilver	8M0134484
Mercury	46-8M0122064
Tohatsu	3RS-87322-1

Engine & Model Compatibility

Confirm your engine model/year in the table below.

For Mercury/Mariner models, this kit fits 2020 and newer 9.9-20 HP 4-stroke engines with serial number 0R833820 and above.

Brand	Model	Rated HP	Stroke	Years	OEM Part No.	Notes
Mercury	9.9 HP EFI	9.9	4-Stroke	2020+	8M0135821/8M0137849	S/N 0R833820 and above
Mercury	10 HP EFI	10	4-Stroke	2020+	8M0135821/8M0137849	S/N 0R833820 and above
Mercury	15 HP EFI	15	4-Stroke	2020+	8M0135821/8M0137849	S/N 0R833820 and above
Mercury	20 HP EFI	20	4-Stroke	2020+	8M0135821/8M0137849	S/N 0R833820 and above
Mercury	ProKicker	9.9-20	4-Stroke	2020+	8M0135821/8M0137849	333cc, 2-cylinder variants
Mercury	SeaPro	9.9-20	4-Stroke	2020+	8M0135821/8M0137849	333cc, 2-cylinder variants

This kit may also fit certain Nissan/Tohatsu models. Use the part numbers for cross-reference only and verify fitment independently.

Brand	Model	Rated HP	Stroke	OEM Part No.	Notes
Tohatsu	MFS	15	4-Stroke	3RS-87322-1	Cross-reference only
Tohatsu	MFS	20	4-Stroke	3RS-87322-1	Cross-reference only

Technical Specs

Product Type: Water Pump Impeller Repair Kit
Installation: Direct replacement for OEM parts
Housing Material: Corrosion-resistant marine alloy
Connection: Direct fit to impeller housing
Warranty: 12 months (aftermarket); Mercury OEM parts carry standard Mercury warranty
Other Technical Attributes: Designed for durability with improved flexibility across varying water temperatures

What’s in the Box

1 x Water Pump Impeller (key component in repair kit)
1 x Impeller Housing
1 x Face Plate
1 x Gasket
1 x Key
1 x Seal
Multiple x O-rings, grommets, and washers (exact quantities vary by manufacturer)

Note: Silicone grease, glycerin, or dish soap recommended for installation but not included in kit.

Installation Notes

Disconnect the battery and shift the outboard into neutral.
Remove the lower unit (gearcase) by unbolting it from the engine's midsection.
Unbolt and remove the old water pump housing assembly.
Carefully note the orientation of the old parts, then remove the old impeller, key, gaskets, and plate.
Clean all mating surfaces thoroughly, ensuring no old gasket material remains.
Install the new face plate, gaskets, and seals. Place the new key on the driveshaft.
Apply a lubricant (like glycerin or dish soap) to the inside of the new housing and slide the new impeller into it while turning the driveshaft clockwise to bend the vanes correctly.
Secure the new housing assembly with the provided bolts, tightening them to the manufacturer's specified torque.
Reinstall the lower unit, ensuring the driveshaft, shift shaft, and water tube align correctly.
Once assembled, start the engine in water and verify a strong, steady stream from the tell-tale outlet.

Troubleshooting & FAQ

How do I confirm this kit fits my specific Mercury engine?

This kit is for 9.9-20 HP four-stroke models (2020 and newer). The most important check is your engine's serial number. It must be 0R833820 or higher. If your serial number is lower, this kit will not fit.

What are the signs of a failing water pump impeller?

Common signs include the engine overheating at idle or low speeds, a weak or intermittent water stream from the "tell-tale" outlet, and in severe cases, a steam or high-temperature alarm from your console.

How often should I replace my outboard's impeller?

As a general maintenance guideline, we recommend replacing the impeller every 1 to 2 years, or every 100 to 200 hours of operation. This interval may be shorter if you frequently operate in sandy, silty, or saltwater conditions.

Is any special lubricant needed for installation?

Yes, applying a lubricant to the impeller and inside the housing makes installation easier and prevents damage to the impeller on the first dry start. We recommend marine-grade glycerin, silicone grease, or even simple dish soap. Do not use petroleum-based grease.

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

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 QC.

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