How to Tell If Your Outboard Water Pump Is Bad

The engine water pump is a vital part of an outboard. However, some boat owners don’t know the crucial things they need to know about water pumps. Many boaters can’t tell when they have a depraved outboard water pump. Others can’t even remember when last they had it serviced or replaced. The vital parts of an outboard water pump need regular servicing to sustain their condition. Water pump impellers and marine engine cooling drive help in maintaining the condition of an outboard boat’s engine.

Common Causes Of Faulty Outboard Water Pump

The engine water pump impeller is the most common cause of overheating and water circulation issues. It is a small, round disc with spinning blades that help to channel water throughout the circuit of the outboard motor. The water supply stops when it becomes faulty causing an overheated engine.

There are three common ways to identify if an outboard water pump might be failing which includes:

The Outboard Motor overheats

Rising outboard motor’s water temperature is a clear indicator of a potential problem. If the motor refuses to produce a steady flow of water, even after it has reached the right operating temperature, the impeller might be worn or completely damaged. The second possible cause although rare is wasps. Wasps sometimes like to eat into the cooling water outlet, especially during winter.

Overused Impeller

You should always inspect your impeller each spring when preparing your boat engine water pump. The Impeller has a service life of approximately 300 work hours or three years max. Now you know how long you should use your impeller before changing.

Reduced Stream Of Water From The Cooling Water Outlet

During your first outing of the season, you may notice a lower than usual stream of water from the cooling water outlet, this might be another possible indicator of damage caused by wasps. To ascertain this, you are advised to insert a thin wire into the outlet and check around for damages. If you notice this fault on your second or third outing then it might be caused by a faulty impeller or damaged pump.

How To Replace An Outboard Water Pump 

Outboard water pumps are like every other motor, its parts and components also get broken or damaged and will require replacing. The maintenance schedule for your outboard water pump can be seamlessly found in the operator’s manual. Below is a rough breakdown of how you can remove and replace an old outboard water pump.

Step 1

Change the motor into reverse gear

Step 2

Remove the mounting bolts securing the lower unit to the midsection and other bolts on the trim tab. Disconnect the shift rod while referring to your manual for directives.

Step 3

Take out the lower unit and bolts on the pump housing and gently remove the engine water pump housing and impeller from the gear case.

Step 4

Install the marine engine water pump wear plate and gaskets on the gear case after carefully reading the instructions for installing. Remember to a proper sealer to avoid leaks on the gasket.

Step 5

Lubricate the impeller cup, driveshaft and keyway then install the impeller to line up with the impeller key.

Step 6

Install the water pump housing. The driveshaft should be turned while placing the housing on top of the impeller. Line up the water tube, driveshaft, and shift rod while installing the lower unit, and don’t overtight the housing’s mounting screw.

Step 7

Install the marine water pump housing, lubricate and reinstall the bolts connecting the midsection and lower unit then run the motor and flush it to ensure a constant stream of water.

Final Note

How often you should change your outboard water pump generally depends on how you use it and the manufacturer’s recommendation. The part of the water pump that requires much attention is the impeller. Most mechanics and manufacturers propose that impellers shouldn’t be used for more than three years. Water pump repair kits can be purchased for as low as $100 including the impeller and would save you a huge amount of money if you can do the installation yourself.


Hilligoss, M. &. (2021). Bornagain boating. Retrieved from Signs of a bad outboard water pump and maintenance tips:

Media, K. (2021). Retrieved from Great Lakes Scuttlebutt:

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