Water Pump Repair Kit - Fits Mercury/Mariner 2-Stroke 30-70HP Outboards (Replaces 77177A3, 46-77177A3)

Water Pump Repair Kit – Fits Mercury/Mariner 2-Stroke 30–70HP Outboards (Replaces 77177A3, 46-77177A3)

This complete water pump repair kit is designed for Mercury and Mariner 2-stroke outboard motors in the 30–70 HP range, manufactured from 1977 through 1997. The kit includes all necessary components to rebuild the water pump assembly for reliable cooling performance.

This kit is a direct replacement for Mercury/Mariner part numbers 77177A3 and 46-77177A3, as well as several aftermarket equivalents.

• Includes a new impeller, upper and lower housings, face plate, gaskets, and seals for a complete overhaul.
• Engineered as a direct replacement part for straightforward installation.
• Compatible with Mercury and Mariner 2-stroke outboard cooling systems within the specified horsepower range.

Part Number Cross-Reference

Use this table to confirm equivalent part numbers across OEM and aftermarket brands.

Compatible Engine Models

Confirm your engine model/year in the table below. For Mercury owners, here’s a guide to help you identify your engine’s serial/model: Mercury Serial Number Guide. You can also review exploded diagrams to verify part numbers: Mercury Parts Diagrams & Catalog.

Technical Specifications

Package Contents

• 1 x Upper Pump Housing (18-3118)
• 1 x Lower Pump Housing/Water Pump Base (18-3424)
• 1 x Impeller (18-3007)
• 1 x Face Plate (18-3107)
• 1 x Drain Gasket (18-2945)
• 1 x Lower Water Pump Base to Face Plate Gasket (18-2823)
• 1 x Upper Face Plate to Body Gasket (18-2824)
• 1 x Water Pump Base Gasket (18-2825)
• 1 x Water Pump Base Gasket (18-2841)
• 1 x Drain Plug (18-2948)
• 1 x O-Ring (18-7155)
• 1 x O-Ring (18-7174)
• 1 x O-Ring (18-7115)

Installation Guide

1. Safety First: Disconnect the engine's battery and remove the spark plug wires.
2. Drain Lubricant: Place a drain pan under the lower unit and remove the upper and lower gear lube drain screws to drain the lubricant.
3. Remove Lower Unit: Remove the bolts securing the lower unit (gearcase) to the engine's midsection and carefully lower it.
4. Disassemble Pump: Unscrew the bolts on the water pump housing and lift it off. Remove the old impeller, wear plate, and gaskets. Note their orientation.
5. Clean Surfaces: Thoroughly clean all mating surfaces on the driveshaft and lower unit, removing any old gasket material or corrosion.
6. Install New Components: Place the new base gasket and face plate over the driveshaft. Insert the new drive key into the driveshaft.
7. Install Impeller: Slide the new impeller down onto the driveshaft, turning the shaft clockwise to help the vanes flex correctly.
8. Reassemble Housing: Apply a light coat of marine grease to the inside of the new pump housing. Install the new upper gasket and press the housing down over the impeller.
9. Secure Housing: Align the bolt holes and tighten the housing bolts to the manufacturer's recommended torque.
10. Reinstall Lower Unit: Guide the lower unit back into place, ensuring the driveshaft, shift shaft, and water tube align correctly. Secure it with the bolts.
11. Refill and Test: Refill the lower unit with fresh gear lube. Reconnect the battery and test the engine in the water to confirm a strong water stream from the telltale outlet.

Troubleshooting & FAQ

Q: How do I confirm this kit fits my specific engine?

A: The most reliable method is to check your engine's serial number against the ranges listed in the "Compatible Engine Models" table above. For example, this kit fits 35 HP Mercury/Mariner outboards with serial numbers 6445653 and up. Please use our linked serial number guide to identify your engine if you are unsure.

Q: What are the signs of a failing water pump?

A: Common signs of a worn or failed impeller include the engine overheating at idle or low speeds, a weak or intermittent water stream from the "telltale" outlet, and, in severe cases, steam coming from the exhaust. Do not run the engine if you suspect an cooling issue.

Q: How often should the water pump assembly be replaced?

A: For preventative maintenance, it is recommended to inspect the impeller annually and replace the entire water pump kit every 1-2 years or every 100-200 hours of operation. This interval may be shorter if you frequently operate in saltwater or water with heavy sediment.

Q: OEM vs. Aftermarket?

A: This listing is an aftermarket replacement part (not an OEM component). We build to OEM specifications using comparable-grade materials. Production is done in an ISO9002-certified facility, and each batch is inspected for consistent performance.

Q: How fast do you ship and how much does it cost?

A: We offer fast global shipping—typically 5–15 days worldwide—and standard shipping is free. Expedited options are available at checkout depending on your location.

Q: What is your warranty and return policy?

A: This product includes a 1-year warranty against manufacturing defects under normal use. If something goes wrong, contact our support team with your order details. Returns are accepted within our standard return window (unused & in original condition); please see our policy page or reach out for instructions.

Important Notes

• Verify that the product images and specifications match your original part. If discrepancies exist—even if your model is listed—do not proceed with the purchase.
• This product is an aftermarket replacement part and is not an OEM component.
• Professional installation is recommended to ensure safety and optimal performance.

Why Choose JLM MARINE?

• Quality Assured: As a trusted manufacturer for over 20 years, we supply top marine brands globally.
• Fast Global Shipping: Free delivery worldwide in 5–15 days.
• Direct from Manufacturer: Competitive pricing without compromising quality.