Water Pump Impeller Maintenance Kit – Fits Mercury/Mariner/Tohatsu 4–6 HP 4-Stroke – Replaces 8M0120836, 3GR-87500-0
Water Pump Impeller Maintenance Kit – Fits Mercury/Mariner/Tohatsu 4–6 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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Delivery and Shipping
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Water Pump Impeller Maintenance Kit – Fits Mercury/Mariner/Tohatsu ...
Water Pump Impeller Maintenance Kit – Fits Mercury/Mariner/Tohatsu 4–6 HP 4-Stroke – Replaces 8M0120836, 3GR-87500-0 is backordered and will ship as soon as it is back in stock.
Product Details
This Water Pump Impeller Maintenance Kit is intended for cooling-system service on selected Mercury, Mariner, and Tohatsu 4–6 HP 4-stroke outboard engines. Replacing worn water-pump components helps maintain cooling-water circulation and reduce the risk of overheating caused by an aged or damaged impeller.
The kit is listed as a replacement for Mercury part number 8M0120836 and Tohatsu part number 3GR-87500-0. Confirm the part number, engine model, stroke, and serial-number range before ordering.
- Maintenance kit for water-pump service.
- Designed for selected 4–6 HP 4-stroke outboards.
- Aftermarket replacement for the referenced manufacturer part numbers.
- Verify fitment and the supplied component arrangement before installation.
Part Number Matrix
Use these references to compare the replacement against the part being removed. Part-number matching should be combined with engine-model and serial-number verification.
| Brand | Manufacturer Part Number |
|---|---|
| Mercury | 8M0120836 |
| Tohatsu | 3GR-87500-0 |
Engine & Model Compatibility
This replacement is associated with selected Mercury/Mariner and Tohatsu 4–6 HP 4-stroke outboards. The available product information does not establish a complete model-year or serial-number list, so do not rely on horsepower alone to confirm fitment.
| Brand | Rated HP Range | Stroke | Reference Part Number | Fitment Note |
|---|---|---|---|---|
| Mercury | 4–6 HP | 4-Stroke | 8M0120836 | Selected models; verify exact model and serial number. |
| Mariner | 4–6 HP | 4-Stroke | 8M0120836 | Selected models; verify exact model and serial number. |
| Tohatsu | 4–6 HP | 4-Stroke | 3GR-87500-0 | Selected models; verify exact model and serial number. |
Technical Specs
- Product Type
- Water pump impeller maintenance kit
- Application
- Cooling-system maintenance for selected outboard engines
- Engine Range
- Selected Mercury/Mariner/Tohatsu 4–6 HP 4-stroke models
- Replacement References
- Mercury 8M0120836; Tohatsu 3GR-87500-0
- Product Status
- Aftermarket replacement, not an OEM-branded component
What’s in the Box
- 1 × Water pump impeller maintenance kit
Component quantities and exact contents can vary by kit configuration. Compare the supplied parts with the original water-pump assembly before beginning installation.
Installation Notes
- Review the engine service manual and confirm that the replacement references and engine application match your outboard.
- Disconnect the battery where applicable, remove the engine cover, and place the outboard in a safe, stable position.
- Shift the outboard into neutral if required by the service procedure.
- Remove the lower unit according to the manufacturer’s instructions, noting any shift-shaft, water-tube, and wiring connections.
- Locate the water-pump housing on the upper portion of the gearcase and remove the retaining fasteners.
- Remove the existing housing components and impeller. Inspect the housing, wear surfaces, keyway, driveshaft, and water tube for damage or excessive wear.
- Clean the mating surfaces and install the replacement components in the same arrangement as the original assembly. If a separate impeller key is required, reuse or replace it according to the service manual.
- Install the impeller with the correct direction of vane rotation for the engine and apply only lubricants approved by the manufacturer.
- Reassemble the water-pump housing and tighten the fasteners to the manufacturer’s specified torque.
- Reinstall the lower unit, ensuring correct alignment of the driveshaft, water tube, and shift mechanism.
- Secure all connections and fasteners, then test the engine in water or with an appropriate flushing device.
- Confirm a steady tell-tale stream and monitor the engine for leaks or overheating before returning it to service.
Troubleshooting & FAQ
How do I know if this maintenance kit fits my engine?
Check that your engine is a compatible Mercury, Mariner, or Tohatsu 4–6 HP 4-stroke model and that the existing water-pump part number matches 8M0120836 or 3GR-87500-0. Because model and serial-number coverage may vary, verify the exact engine model and serial number against the manufacturer’s parts information before ordering.
What are the signs of a failing water-pump impeller?
Common symptoms include a weak or intermittent tell-tale stream, an overheating warning, unusually high operating temperature, or reduced cooling-water flow. Stop operating the engine if it overheats and inspect the cooling system before further use.
How often should the water-pump impeller be inspected?
Inspect and service the impeller according to the engine manufacturer’s maintenance schedule. Frequent use in saltwater, sand, or silt can increase wear and may require more frequent inspection.
Can I replace only the impeller?
That depends on the condition of the remaining water-pump components and the contents of the supplied kit. Inspect the housing, wear surfaces, gaskets, and impeller key, and replace worn or damaged parts as required by the service manual.
Is this an OEM part?
No. This listing is for an aftermarket replacement maintenance kit associated with Mercury part number 8M0120836 and Tohatsu part number 3GR-87500-0. Mercury and Tohatsu are referenced only for compatibility and part-number identification.
What are your shipping speed and cost?
Standard shipping is free, and expedited options may be shown at checkout when available for your location. Delivery timing depends on destination, carrier, and service selected.
What is the warranty and return policy?
See the current store warranty and return-policy terms for eligibility, time limits, and required conditions. Contact support before returning a product if you need installation or fitment assistance.
Safety & Important Information
- Confirm the exact engine model, year where applicable, stroke, and serial-number range before purchase.
- Do not operate an outboard without a proper cooling-water supply.
- Follow the manufacturer’s service manual for disassembly, torque values, lubrication, and testing.
- Stop operation immediately if the tell-tale stream is weak or the engine shows signs of overheating.
- This is an aftermarket replacement, not an OEM-branded component.
- Professional installation is recommended if you are not familiar with lower-unit or water-pump service.
About Sea Sierra
- Marine Maintenance Parts — Replacement components for routine outboard service and repair.
- Fitment-Focused Support — Compare part numbers and engine details before ordering.
- Convenient Fulfillment — Shipping options and delivery estimates are shown at checkout based on destination.
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