Raw Water Pump Replacement: A Step-by-Step Guide for Boaters

Introduction

The raw water pump plays a vital role in your boat's engine cooling system, ensuring optimal performance and preventing costly damage. Regular replacement of the raw water pump or its components is essential to avoid overheating and maintain the overall health of your boat's marine engine. Over time, components within the pump such as the raw water impeller, seals, and gaskets can degrade due to friction and exposure to debris in the water. If left unchecked, a worn seawater pump can fail, leading to engine overheating and costly repairs.

Understanding Your Raw Water Pump

What Is a Raw Water Pump?

A raw water pump, whether it's a bronze sea water pump or another material, circulates water from the surrounding environment (lake, river, or ocean) through the engine's heat exchanger to keep it cool. This prevents the engine from overheating and ensures it runs efficiently. These pumps draw water from the sea and circulate it through the engine's heat exchanger.

Key Components of a Raw Water Pump

Key components of the engine cooling pump include:

• Impeller: The flexible impeller that spins inside the pump to move water through the cooling system.

• Pump Body: The main housing that contains the impeller and other internal parts.

• Cover Plate: Secures the impeller inside the pump body.

• Mounting Hardware: Bolts, screws, and pump bracket used to attach the pump to the engine.

• Pump shaft: The axis around which the impeller rotates.

Signs It’s Time for a Replacement

Common Indicators of Wear

Keep an eye out for these common signs that your raw water pump may need attention:

• Reduced water flow: Less water coming out of your engine’s exhaust.

• Unusual noises: Squeaking or grinding sounds from the pump.

• Engine overheating: The engine frequently overheats.

• Visible wear: Cracks, missing blades, or other damage on the raw water impeller.

• Leaks: Water or oil leaks around the pump.

Recommended Replacement Intervals

Impellers should be replaced every 1-2 years or approximately every 250 hours of operation, depending on usage and water conditions. Some boaters inspect and fully rebuild their pump every 4 to 5 years, while others may opt to replace the impeller more frequently.

Tools and Materials Needed

Essential Tools

• Screwdriver set

• Wrenches or socket sets

• Pliers

• Impeller puller: A tool specifically designed to remove the impeller from the water pump housing1.

• Marine grease

• Clean rag

• Gasket scraper

• Hose barb fitting

Replacement Parts

• New impeller kit, including impeller, gaskets (avoid cheap paper gaskets), O-rings, and lubricant.

• Additional replacement hardware (if needed).

• Engine seal, oil seal, or shaft seal if leaks are present.

• Gasket sealer or silicone gasket maker.

Safety Equipment

• Gloves

• Safety goggles

Step-by-Step Raw Water Pump Replacement Process

Preparation and Safety Measures

Draining the Engine Cooling System

Always start by ensuring the engine is turned off and completely cool. Once cool, drain the raw water from the cooling system by opening the drain plug on the engine. This will prevent any unwanted water flow when you remove the pump.

Securing the Boat and Engine

Make sure the boat is stable and secure before beginning any work in the engine compartment.

Removing the Old Pump

Removing the Screws and Mounting Hardware

Locate the Mounted Raw Water Pump on your engine. Depending on your engine model, it’s usually mounted on the front or side. Loosen the bolts or screws holding the pump in place and carefully disconnect the hoses attached to the hose barb on the pump. Be sure to take note of which hose goes where for reinstallation later.

Pry the Cover Plate Off

To start, remove the cover plate from the housing. Accessing the impeller or replacing it will almost always require replacement of the cover plate gasket or O ring.

Removing the Old Impeller

Use an impeller puller to carefully remove the old impeller. If it’s been a while since your last pump service, the impeller may be stiff and require a little extra force to remove. For impellers that are equipped with threads, jacking screws can be used for removal.

Inspecting the Pump Body for Wear

Once the impeller is removed, inspect the pump housing for signs of wear or damage. Clean the inside of the housing with a rag to remove any debris or build-up. Also check the sealing surfaces.

Installing the New Pump/Impeller

Cleaning the Pump Cover Plate

Clean the pump cover plate to ensure a good seal with the new gasket.

Installing the New Impeller Kit

Take the new impeller from your rebuild kit and apply a light coating of marine grease to the blades. This will help lubricate the impeller and ensure it fits smoothly inside the pump housing. Next, replace the old seals and gaskets with the new ones provided in the rebuild kit. Be sure to install them in the correct positions and use marine grease to lubricate the seals before inserting them.

Reassembling the Pump and Securing It in Place

Carefully place the new impeller inside the housing, making sure the blades are bending in the correct direction. Replace the cover plate and tighten the screws securely. Reconnect the hoses to the pump, ensuring they are in the correct positions. Secure the pump back in place on the engine by tightening the bolts or screws you removed earlier.

Post-Installation Testing

Checking for Leaks and Proper Water Flow

Once the pump is reinstalled, refill the cooling system with water. Start the engine and check for leaks around the pump.

Verifying Engine Cooling Performance

Let the engine run for a few minutes to ensure the pump is working correctly and water is flowing through the system as it should. Also, monitor the engine temperature to ensure it remains within the normal operating range.

Troubleshooting and Maintenance Tips

Common Installation Issues and How to Fix Them

• Stubborn screws: Use penetrating oil and the correct size screwdriver to avoid stripping the heads.

• Misaligned parts: Double-check the orientation of all components before tightening.

• Damaged pump components: Replace any worn or damaged parts immediately.

Preventative Maintenance

• Regular visual inspections: Check the pump and impeller for wear and tear during routine maintenance.

• Scheduled replacement intervals: Adhere to manufacturer recommendations for impeller and pump replacement.

When to Seek Professional Assistance

If you’re uncomfortable performing the replacement yourself or encounter significant issues, consult a qualified marine mechanic or Fisheries Supply. A press is sometimes needed to remove bearings.

Frequently Asked Questions (FAQ)

How often should I replace my raw water pump impeller?

Impellers should be replaced every 1-2 years or approximately every 250 hours of operation, depending on usage and water conditions.

Can I reuse the pump body with a new impeller?

Yes, if the pump body is in good condition (no cracks, corrosion, or significant wear).

What are the warning signs of pump failure?

Common signs include engine overheating, reduced water flow, unusual noises, and visible leaks.

Are there differences between pump models I should consider?

Yes, different engines require specific pump models. Always use the engine manufacturer-recommended replacement. Oberdorfer Pumps and Depco Pump are some of the manufacturers of the pumps.

Conclusion

Summary of Key Steps and Benefits

Proper raw water pump replacement ensures your boat's engine stays cool, preventing damage and maintaining optimal performance. Regular maintenance and timely replacements can save you money and provide peace of mind on the water. Carrying a spare pump is also a good idea.

Final Recommendations

Perform routine inspections and replace the impeller or pump as needed. Consult with marine professionals if you encounter any issues beyond your comfort level.

Additional Resources

Consult your engine's manual for specific instructions and recommendations.