The Importance of a Water Pump

Water pump impellers.

Most people understand the importance of regular boat maintenance, such as changing the oil in the engine and lower unit, but they struggle with changing their water pump. I think this is because they don’t understand the difference between the water pump in their car and the one on their outboard motor.

A car’s water pump is a closed loop using freshwater and anti-freeze. Nothing is being pumped through the system from the outside environment. The pump itself is under the hood of the vehicle, and the outside housing is never submerged (unless the car is driven into the water). Coolant is changed about every 65,000 miles, and in some vehicles 100,000 miles.

Usually, when a vehicle’s water pump fails or starts to fail, puddles of anti-freeze can be spotted on the ground. A driver may also notice the car running hot by the temperature gauge. In some cases the vehicle will completely overheat, spilling coolant everywhere, but most drivers stop the vehicle before any major damage is done.

An outboard water pump is very different, especially when you consider saltwater—one of the most corrosive environments on the planet. This coolant is not only saltwater, but also whatever may be in the water, including sand, mud, shells, and more. The entire pump housing is submerged in this environment, as well.

An outboard motor has either a metal or plastic housing with a rubber impeller that looks like a starfish. It rotates at the speed of the driveshaft drawing water through it and to the rest of the motor to keep it cool. If it sucks up sand or mud, it sends it through the rest of the engine, and, in most cases, those items exit out the “pee hole.”

Over time, this debris takes a toll on the water pump and housing, causing the pump to lose flow or volume, which results in the engine running hotter and eventually causing it to overheat. Due to gravity, once the pump quits on an outboard, all coolant (saltwater) leaves the engine. This can cause the engine’s temperature to spike, resulting in costly internal damage.

I recommend to most my customers they change their water pump every other year, and if they fish in shallow water and pump a lot of sand and mud, then I recommend every year. The cost on average is $250, but a water pump keeps a $10,000 to $20,000 piece of equipment running correctly. The other benefit of changing the water pump every other year is it allows either you or the technician to clean and lubricate the mounting bolts for the lower unit. I have seen my technicians spend eight hours (which the customer is paying for) on breaking a lower unit loose to get to a water pump because the customer thought they were saving money by not changing their water pump for five years. However, they failed to realize that salt was building up in the mounting bolts and causing them to swell.

A little preventive maintenance will save you big in the future. See you on the water.

Chris Butler is the owner of Butler Marine and has been boating and fishing for 15 years. Chris can be reached at Butler Marine at (843) 522-9461 or