Mercury Heavy Duty Impeller Kit – Fits MerCruiser 4.5L & 6.2L Engines (Replaces 98-8M0121940)
Mercury Heavy Duty Impeller Kit – Fits MerCruiser 4.5L & 6.2L Engines (Replaces 98-8M0121940) 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
Mercury Heavy Duty Impeller Kit – Fits MerCruiser 4.5L & 6.2L E...
Product Details
This Mercury Heavy Duty Impeller Kit is a complete service replacement part for the sea water pump in Mercury MerCruiser 4.5L & 6.2L engines (serial numbers 2A531163 and above). It ensures your engine's cooling system operates reliably under demanding marine conditions.
This aftermarket kit is a direct replacement for Mercury part numbers 98-8M0121940, 47-8M0137221, 8M0121940, and 8M0137221. It also interchanges with GLM part numbers 89703 and 89704.
- Features a heavy-duty impeller design for enhanced durability and performance.
- Engineered as a direct-fit service replacement for specified MerCruiser models.
- Complete kit includes the impeller and necessary wear plates for a full restoration.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket.
| Brand | Part Number | Superseded By | Notes |
|---|---|---|---|
| Mercury | 98-8M0121940 | 47-8M0137221 | |
| Mercury | 8M0121940 | 8M0137221 | |
| GLM | 89703 | Aftermarket Interchange | |
| GLM | 89704 | Aftermarket Interchange |
Engine & Model Compatibility
Confirm your engine model and serial number in the table below.
For Mercury MerCruiser engines, verifying your engine's serial number against the listed range is critical for ensuring correct fitment.
| Brand | Model | Stroke | OEM Part No. | Notes |
|---|---|---|---|---|
| Mercury | MerCruiser 4.5L | 4-Stroke | 98-8M0121940 | Serial numbers 2A531163 and above, Superseded by 47-8M0137221 |
| Mercury | MerCruiser 6.2L MCM (sterndrive) | 4-Stroke | 98-8M0121940 | Serial numbers 2A531197 and above, Superseded by 47-8M0137221 |
| Mercury | MerCruiser 6.2L MIE (inboard) | 4-Stroke | 98-8M0121940 | Serial numbers 2A530774 and above, Superseded by 47-8M0137221 |
| Mercury | MerCruiser 6.2L TowSport | 4-Stroke | 98-8M0121940 | Serial numbers 2A531348 and above, Superseded by 47-8M0137221 |
Technical Specs
- Product Type
- Heavy Duty Impeller Kit
- Installation
- Service replacement
- Dimensions
- Height: 8.0 in; Width: 12.0 in; Length: 17.0 in
- Key Feature
- Heavy duty impeller design
What’s in the Box
- 1 x Shorter Heavy Duty Impeller (Replaces 47-8M0137221)
- 1 x Rear Wear Plate
- 1 x Overmolded Inner (Front) Wear Plate
Installation Notes
- Disconnect the boat's battery and close the engine's raw water intake valve (seacock).
- Loosen the hose clamps and carefully remove the hoses from the sea water pump.
- Unscrew the pump housing cover bolts to access the impeller.
- Remove the old impeller and the front/rear wear plates. An impeller puller tool may be needed.
- Thoroughly clean the inside of the pump housing, checking for and removing any debris or old impeller fragments.
- Install the new rear and front wear plates into the pump housing.
- Lightly lubricate the new impeller and housing interior with a water-based lubricant or liquid soap.
- Insert the new impeller, rotating the driveshaft in the engine's direction of operation to correctly bed the vanes.
- Reinstall the housing cover with its gasket/o-ring, tighten bolts to spec, and reattach hoses.
- Open the seacock, reconnect the battery, start the engine, and immediately check for proper water flow and any leaks.
Troubleshooting & FAQ
How do I confirm this impeller kit fits my engine?
This kit fits specific Mercury MerCruiser 4.5L and 6.2L engines. The most important check is your engine's serial number. Please find your serial number on the engine block or flame arrestor cover and compare it to the ranges listed in the compatibility table.
What are the signs of a failing impeller?
Common symptoms include the engine overheating (especially at idle), a noticeably weaker stream of water from the exhaust outlet, or, upon inspection, impeller vanes that are cracked, brittle, or have separated from the hub.
How often should I replace my engine's impeller?
For preventative maintenance, it's recommended to replace the impeller every 1 to 2 years or every 100-200 hours of operation. Intervals should be shorter in saltwater or silty/sandy water conditions. Always consult your engine's service manual for official guidance.
What is a "heavy-duty" impeller?
A heavy-duty impeller is made from a more robust polymer compound that offers greater resistance to wear, heat, and chemical breakdown compared to a standard impeller. This enhances durability and is ideal for high-performance or commercial applications.
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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