Water Pump Repair Kit – Fits Mercury 9.9–20 HP 4-Stroke (Replaces 8M0135821, 98-8M0135821, 8M0137849, 3RS-87322-1)
Water Pump Repair Kit – Fits Mercury 9.9–20 HP 4-Stroke (Replaces 8M0135821, 98-8M0135821, 8M0137849, 3RS-87322-1) is backordered and will ship as soon as it is back in stock.
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Worry-free returns
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
Delivery and Shipping
Free standard shipping on all orders under 1 KG
Water Pump Repair Kit – Fits Mercury 9.9–20 HP 4-Stroke (Replaces 8...
Product Details
This Water Pump Repair Kit is designed for Mercury 4-Stroke 9.9–20 HP outboard engines with serial numbers 0R833820 and above, including ProKicker and SeaPro models. It provides all necessary components to restore the engine's cooling system to factory specifications.
It serves as a direct replacement for Mercury/Quicksilver part numbers 8M0135821 and 98-8M0135821, Mercury 8M0137849, and Tohatsu 3RS-87322-1.
- Engineered to meet original equipment manufacturer (OEM) specifications for reliable performance.
- Includes a new impeller, upper and lower housings, and plate for a complete overhaul.
- Installation is a direct replacement process requiring common shop tools.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number | Notes |
|---|---|---|
| Mercury / Quicksilver | 8M0135821 | Primary reference number |
| Mercury / Quicksilver | 98-8M0135821 | |
| Mercury | 8M0137849 | |
| Tohatsu | 3RS-87322-1 | Cross-references to Mercury 8M0135821 |
Engine & Model Compatibility
Confirm your engine model and serial number in the table below. Verification is critical for proper fitment.
| Brand | Model | Rated HP | Stroke | Years / Serial No. | OEM Part No. | Notes |
|---|---|---|---|---|---|---|
| Mercury | 4-Stroke Outboards | 9.9 | 4-Stroke | 0R833820 and above | 8M0135821 | Includes ProKicker and SeaPro models |
| Mercury | 4-Stroke Outboards | 10 | 4-Stroke | 0R833820 and above | 8M0135821 | Includes ProKicker and SeaPro models |
| Mercury | 4-Stroke Outboards | 15 | 4-Stroke | 0R833820 and above | 8M0135821 | Includes ProKicker and SeaPro models |
| Mercury | 4-Stroke Outboards | 20 | 4-Stroke | 0R833820 and above | 8M0135821 | Includes ProKicker and SeaPro models |
| Mercury | 2-Cylinder (333cc) | 9.9-20 | 4-Stroke | 8M0135821 | For 2-Cylinder 333cc engines | |
| Tohatsu | MFS | 15 | 4-Stroke | 3RS-87322-1 | Cross-reference to Mercury 8M0135821 | |
| Tohatsu | MFS | 20 | 4-Stroke | 3RS-87322-1 | Cross-reference to Mercury 8M0135821 |
Technical Specs
- Product Type
- Water Pump Repair Kit
- Installation
- Direct replacement, requires common shop tools
- Connection
- Direct fit to lower unit
- Package Dimensions
- Length: 4.25 in (108 mm), Width: 4.50 in (114 mm), Height: 6.25 in (159 mm)
- Weight
- 0.63 lb (0.29 kg)
- Manufacturing
- Produced to meet Mercury Marine original equipment manufacturer specifications
- Warranty
- 1 Year (from select retailers)
What’s in the Box
This kit includes the following components for a full assembly:
- 1 x Water Pump Impeller
- 1 x Upper Housing
- 1 x Lower Housing
- 1 x Plate
Installation Notes
- Disconnect the battery and shift the outboard into neutral.
- Remove the lower unit (gearcase) by unbolting it from the engine's midsection. You may need to disconnect a shift shaft or speedometer tube.
- Locate the water pump assembly on top of the gearcase and remove the bolts securing its housing.
- Carefully lift off the old housing and remove the old impeller, key, gaskets, and wear plate.
- Clean all mating surfaces thoroughly, ensuring they are free of old gasket material and corrosion.
- Install the new wear plate and gaskets as provided in the kit.
- Slide the new impeller onto the driveshaft (turn the shaft clockwise to ease installation) and insert the drive key.
- Lubricate the inside of the new housing and install it over the impeller, ensuring a proper seal.
- Tighten the housing bolts to the manufacturer's specified torque.
- Reinstall the lower unit, carefully reconnecting any shift shafts or water tubes.
- Once assembled, test the engine using a water source (flushing muffs) to confirm water is pumping correctly from the tell-tale outlet.
Troubleshooting & FAQ
How do I confirm this kit fits my engine?
This kit is for Mercury 4-Stroke 9.9–20 HP outboards with serial number 0R833820 or higher. Always verify your engine's serial number, usually found on the transom bracket, against our compatibility table before ordering.
What are the signs of a failing water pump?
Common symptoms include a weak or intermittent water stream from the "tell-tale" outlet, engine overheating alarms, and a dry-rotted or cracked impeller found during inspection. A healthy water pump is critical for engine cooling.
How often should I service the water pump?
As a best practice, inspect and replace the water pump impeller every one to two years or every 100-200 hours of use. Service intervals should be shorter if operating in saltwater or in water with heavy sand or silt content.
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.
Payment & Security
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