Water Pump Impeller Kit – Fits Mercury/Tohatsu 4/5/6 HP 4-Stroke (Replaces 8M0120836, 3GR-87500-0)
Water Pump Impeller Kit – Fits Mercury/Tohatsu 4/5/6 HP 4-Stroke (Replaces 8M0120836, 3GR-87500-0) 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 Impeller Kit – Fits Mercury/Tohatsu 4/5/6 HP 4-Stroke (R...
Product Details
This Water Pump Impeller Kit is designed for cooling system maintenance on select Mercury/Mariner and Tohatsu 4, 5, and 6 HP 4-stroke outboard engines. It ensures your engine's cooling system operates efficiently, preventing overheating and potential damage.
It serves as a direct replacement for Mercury part number 8M0120836 and Tohatsu part number 3GR-87500-0.
- Engineered for direct-fit installation.
- Crucial for routine cooling system service.
- Includes core components for impeller replacement.
Part Number Matrix
Use this matrix to confirm equivalent references across OEM and aftermarket suppliers.
| Brand | Part Number |
|---|---|
| Mercury | 8M0120836 |
| Tohatsu | 3GR-87500-0 |
Engine & Model Compatibility
Confirm your engine model and serial number in the table below.
Fits Mercury/Mariner 4, 5, and 6 HP 4-stroke EFI outboards with serial number 0R411838 and higher.
| Brand | Model | Rated HP | Stroke | OEM Part No. | Notes |
|---|---|---|---|---|---|
| Mercury | 4 HP EFI | 4 | 4-Stroke | 8M0120836 | For serial number 0R411838 and above |
| Mercury | 5 HP EFI | 5 | 4-Stroke | 8M0120836 | For serial number 0R411838 and above |
| Mercury | 6 HP EFI | 6 | 4-Stroke | 8M0120836 | For serial number 0R411838 and above |
Technical Specs
- Product Type
- Water Pump Impeller Kit
- Installation
- Direct replacement
- Other Technical Attributes
- For cooling system maintenance
What’s in the Box
- 1 x Water Pump Impeller Kit (Replaces Mercury 8M0120836/Tohatsu 3GR-87500-0)
Installation Notes
- Disconnect the battery and remove the engine cover.
- Shift the outboard into neutral.
- Remove the lower unit (gearcase) by unbolting it from the main engine leg. Take note of any shift shaft connections.
- Place the lower unit on a workbench and locate the water pump housing, typically found at the top of the unit.
- Remove the bolts securing the water pump housing cover.
- Slide the old housing, impeller, and wear plate off the driveshaft. Clean all mating surfaces thoroughly.
- Install the new gasket, wear plate, impeller (rotate clockwise), and housing.
- Lightly grease the driveshaft and housing interior before reassembly.
- Reinstall the water pump housing cover and torque bolts to manufacturer specifications.
- Reattach the lower unit to the engine, ensuring the driveshaft, water tube, and shift shaft are correctly aligned.
- Secure all bolts and reconnect the battery.
- Test the engine using a water source (flushing muffs or in water) to verify proper water flow from the tell-tale outlet.
Troubleshooting & FAQ
How do I know if this impeller kit fits my engine?
This kit is specifically for Mercury/Mariner and Tohatsu 4, 5, and 6 HP 4-stroke models. For Mercury engines, it is critical that your serial number is 0R411838 or higher. Always cross-reference your existing part number with 8M0120836 (Mercury) or 3GR-87500-0 (Tohatsu) to guarantee fitment.
What are the signs of a failing water pump impeller?
Common symptoms include a weak or intermittent stream from the "tell-tale" water outlet, engine overheating alerts, or a noticeable increase in engine operating temperature. Reduced performance under load can also indicate a cooling problem.
How often should the water pump impeller be replaced?
As a general maintenance rule, the impeller should be inspected annually and replaced every 2-3 years or every 200-300 operating hours, whichever comes first. Usage in saltwater or sandy/silty conditions may require more frequent replacement.
Can I replace just the impeller instead of the whole kit?
While possible, it is highly recommended to replace all components included in the kit. The wear plate, gaskets, and housing are also critical wear items that degrade over time and can cause pressure loss or leaks, leading to premature failure of the new impeller.
Is this an OEM part?
This listing is an aftermarket replacement (not OEM). It is built to OEM-level specifications with comparable materials and manufactured in an ISO 9002 facility, where it is batch-inspected for consistency.
What are your shipping speed and cost?
We ship worldwide quickly—typical transit is 5–15 days. Standard shipping is free, and expedited options will appear at checkout if they are 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 use. If any issues arise, please contact our support team with your order details. Returns are accepted within our standard window for unused items in their original condition. See our policy page or reach out for instructions.
Safety & Important Info
- Verify images and specifications against 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 quality control.
Payment & Security
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