by Bob Van Brunt
- Why did the impeller in my pump go bad?
- How many engine hours should it last?
The sea water pump is a positive displacement pump. They have better suction than the centrifugal pumps, and you don’t have to prime them. They are used for all sea water cooling applications. About 500 engine hours is the average life of an impeller. The Volvo Penta impellers are made of neoprene rubber. There are some aftermarket impellers (blue in color) that are designed to run longer dry without damage.
Check your impeller prior to spring commissioning as part of your pre-launch maintenance. Look for cracks at the base of the fins and for missing fins. Any of these defects warrants replacement of your impeller. Loss of cooling water due to a damaged impeller can cause serious and expensive engine damage.
An impeller may go bad early because it is run dry. Either a through-hull sea valve has shut, or a sea strainer has clogged. You should have a hull strainer and a sea strainer with a removable basket on your boat. If they do not get water, they will burn up in about 30 seconds. Make sure your valves are open and that your strainers are clean before you go out.
The circulation pump is a centrifugal pump. It has a metal impeller that pumps cooling fluid (jacket water or anti-freeze) through the engine. If your circulation pump is leaking fluid from the “tattle-tale” hole, located just below the pulley and shaft assembly, you may have a bad seal and the pump needs to be replaced. Another problem that arises with circulation pumps is the failure of shaft bearings, usually evident from a rattle or “squeal” from the water pump area. The pump bearings can be checked with the engine shut off by checking the movement on the pump pulley. There should be very little, if any, up and down movement. Most people replace circulation pumps thinking that it will solve an overheating problem. This a common mistake. If the pump bearings are fine and the seals are not leaking, there is a good chance that the pump is fine.
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December 1, 2009 / mpartsexpress / 0
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