Try to mount the new impeller with vanes bent in the same directionĢ) Most impellers that are mounted to a shaft are held in place by a small metal key. When installing the new impeller, there are a few things to watch for:ġ) Take note of which direction the impeller blades were bent on the original impeller. If they aren’t visible, they may have made their way into the engine – so take care to flush the engine through to ensure that rubber bits aren’t blocking any cooling passages! If the impeller has cracked, or has pieces missing, try your best to find any missing pieces. There are a number of handy tools that can be used to extract a stuck impeller (in a pinch, a pair of screwdrivers tend to work well). When removing an impeller, space is sometimes limited. The forks pull on the back of the impeller as the screw is turned (pressing on the water pump shaft), forcing the impeller out. The back of the pump can then be taken off, to access the impellerĪlpha: Alpha drives have a set-up similar to most outboards: The lower unit of the drive needs to be removed to access the water pumpīravo: Bravo drives are similar to Volvo drives, with an engine mounted water pump.Ī handy tool to remove an impeller. The water pump can be taken off the engine by removing a few bolts. To locate it, follow the hoses that run from the stern drive, along the underside of the engine. Volvo: These stern drive units have vents similar to outboards and OMC drives, but the water pump is mounted to the front of the engine. A few bolts later, the impeller can be accessed and changed. Once removed, the water pump is accessible. OMC: The water pump is behind a casing at the top of the stern-drive. Each major stern-drive manufacturer uses a different way to mount their water pumps Sterndrives: Stern drives function similar to an outboard drive leg: Water is sucked up through the vents near the propeller, and forced through a water hose into the engine. The impeller is found beneath the casing. To get to it, the bolts securing the lower unit need to be removed (the owners manual should be consulted), the lower unit taken off, and the plastic casing of the water pump unbolted. The water pump is found inside the leg, between these two halves. Half-way up the leg of the outboard, there are a number of bolts that connect the lower unit to the upper. Outboards – Outboards draw cooling water through a vent at the bottom of the drive leg. The water pump is mounted at the top of the lower unit, at the base of the shaft. Behind the flat plate on the face of the water pump will be the impeller To find the water pump, trace the hose that runs from the seacock (where water enters the boat), to the first place that it clamps onto the engine: This will be the water pump. Inboards – as found on most sailboats, and on powerboats with a prop and shaft set-up. The triangular shaped plate covers the impeller on this engine-mounted water pump on a Yanmar diesel The impeller is the only device to provides the suction and pressure to move the water necessary for engine cooling – and without it working correctly, the engine will overheat.ĭepending on the type of engine, the impeller could be located in a few different places: Additionally, any overheating of the water pump will cause the impeller to break up into small bits. The impeller is pressed tightly into the housing of a water pump, and over time it loses its fit, and the rubber vanes can crack or degrade. There aren’t too many complicated parts to the system, and one of the seasonal maintenance tasks that is necessary is to check the impeller: A small rubber device (similar to a paddle-wheel) that is spun by the engine, sucking water up, into and through the engine. Water is sucked up from the water surrounding the boat, is run through the engine, and out through the exhaust system along with exhaust gases. The marine engine’s cooling system is pretty basic. This is true for inboards, outboards and stern-drives, whether power or sail. What they’re looking for are signs of water exiting with the exhaust: Water exiting means that water is being sucked up and pushed through the engine appropriately – this is the only visual clue that the raw water cooling system is working appropriately. If you’ve spent any time in a boat yard during spring commissioning season, you won’t find it out of place to hear the roar of the engine, a cloud of blue smoke erupt, and a mechanic craning over the stern to look at the exhaust. Note that the vanes are bent - a new impeller will have straight vanes that need to be bent in place to fit.
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