How to Tell if an Outboard Water Pump Has Gone Bad
The water pump is an outboard cooling system component that circulates water through the engine. And when the water pump fails, the effects on the motor are catastrophic.
Water pump failure can easily be prevented, as the main reason it happens is due to a worn out or broken impeller. That part of the water pump assembly is inexpensive and very easy to replace, once the lower unit of the outboard is removed.
Signs an Outboard Water Pump is Bad
Most outboards have open cooling systems that use the water the boat is passing through to keep the engine cool. Salt, sand and debris often get sucked into the cooling system, eating away at the impeller and other parts of the water pump over time.
One sign that your outboard’s water pump is going bad is hearing a grinding or rattling sound coming from the engine due to a damaged impeller, the part that distributes cooling liquid throughout the engine as it spins inside its housing. The small rotating plastic blades of an impeller are prone to cracking and breaking off over time.
When this happens, the impeller won’t send enough (or any) cold water through the cooling system, causing the motor to overheat, which is another sign the water pump has gone bad. Chunks of a worn out impeller can break off and get sucked into the engine, which wreaks havoc on the entire outboard.
A broken water pump can also make screeching noises due to worn out bearings. Besides unusual noises, other signs a water pump has gone bad include water leakage, reduced water flow, and as mentioned, engine overheating. An overheating outboard or an usually weak stream of water from the “pee hole” are clear signs of a failing water pump.
How Often Does an Outboard Water Pump Need Replacing?
Once you’ve removed the lower unit to access it, the water pump is easy to replace. Changing out just the impeller or the entire water pump is essentially the same process, since swapping out the impeller requires disassembling the water pump.
The first thing you should do after buying a used outboard is replace the water pump impeller, no matter how new or old the motor is, because doing so once every boating season is recommended. Even if the previous owner says the impeller has been replaced as part of its regular cooling system maintenance, remove the gearcase and pop a new one in anyway just to be safe.
Although the impeller alone is easy to swap out, it’s recommended to just buy a water pump kit and replace the entire assembly. Impellers are notorious for failing, so you should inspect them after every 100 hours of use or once a year and replace them if necessary.
Inspect the impeller for cracks, rotting and deformities, and for broken or missing blades. Water pump impellers are inexpensive, so you should always carry a spare or three on your boat just in case one fails.
It takes approximately one hour to remove the gearcase, swap out the impeller, and then re-install the gearcase, so don’t wait for it to rot and break off into the engine.
