Mercury – Quicksilver Water Pump Base Assembly | Reinforced Nylon with Seal | 803750A04

Overview

A dependable cooling system keeps your engine alive, and that starts at the base. The Mercury Marine 803750A04 Quicksilver Water Pump Base Assembly is built tough to keep water flowing smoothly through your outboard. Made from reinforced nylon and featuring an integrated seal and O-ring, it’s designed to handle years of use in heat, pressure, and saltwater without warping or leaking. It’s a direct replacement for Mercury 9.9HP FourStroke BigFoot, 15HP FourStroke (0R235949 and newer), and 20HP FourStroke (0R235168 and newer) models — the same part Mercury installs at the factory to keep their engines running cool and reliable.

Key Features

• Purpose: Provides a solid, watertight foundation for your engine’s cooling system.
• Construction: Built from reinforced nylon that stands up to vibration, heat, and marine conditions.
• Design: Comes with an integrated seal and O-ring for a clean fit and easy installation.
• Performance: Maintains consistent water pressure to prevent overheating.
• Ease of Use: Direct OEM replacement that bolts right into place.

Engine & Boat Compatibility

• Mercury 9.9HP FourStroke BigFoot
• Mercury 15HP FourStroke (serial number 0R235949 and up)
• Mercury 20HP FourStroke (serial number 0R235168 and up)

Performance & Real-World Benefits

The 803750A04 water pump base helps your outboard keep its cool under pressure. When bases age, they can warp or crack, letting air or water escape — the kind of hidden problem that leads to overheating. Swapping it out restores your cooling system’s integrity, ensuring smooth, consistent flow through the motor.

It’s built from reinforced nylon, a tough, lightweight material that handles marine punishment without deforming. With the seal and O-ring already integrated, there’s no fussing with extra parts or leaks. Once installed, it just works — keeping your outboard cool, quiet, and efficient.

Why Choose Mercury OEM

The Quicksilver 803750A04 isn’t just made to fit — it’s made to last. Aftermarket bases often use cheaper plastics that can flex or distort over time. Mercury’s OEM version uses high-grade materials tested to withstand saltwater, temperature changes, and long run hours.

This is the same base Mercury technicians rely on at the factory and in the field. It’s built to meet their exact standards for sealing, performance, and long-term reliability. When it comes to cooling, you don’t want “close enough.” You want the real deal.

FAQ

Q1: What’s included in this assembly?
It includes the water pump base, integrated seal, and O-ring — everything you need to install.

Q2: Why should I replace the water pump base?
A warped or cracked base can reduce water pressure and cause overheating. Replacing it restores proper cooling.

Q3: What’s it made of?
It’s made from reinforced nylon, which is lightweight, heat-resistant, and built for marine conditions.

Q4: Is installation difficult?
No — it’s a direct-fit OEM part that goes in easily with standard tools.

Q5: Why use OEM instead of an aftermarket version?
OEM parts fit right the first time and last longer, giving you factory-quality reliability and peace of mind.