Marine Impeller Pump Inspect, Repair and Rebuild

Marine Impeller Pump Inspect, Repair and Rebuild

Inspect, Repair & Rebuild A Marine Impeller Pump

Marine Impeller Pump How to:

If a boat’s engine or generator is raw-water-cooled, then be aware that a marine raw water pump is an all-too-common source of trouble. Blockage in the cooling system or a failure of the pump can cause major damage to a raw-water-cooled engine.

Without enough cooling, an engine can overheat and can be damaged permanently. Proper maintenance of the raw water pump now can help to avoid a mountain of headaches with the boat in the future!

If there is no water flow to cool the engine, then there are several things that need to be  checked. Always run the engine and water pump with an available water source feeding the cooling system; do NOT run the water pump dry. First, if the pump is belt-driven, observe whether the pump pulley is turning when the engine is running. If the pulley is not turning, check, tighten or replace the drive belt. Another possibility could be the pump shaft has become frozen in the pump housing. If so, then the pump needs to be disassembled to determine the failure. If the pulley is turning, then most likely there is an issue with the impeller or pump body. Again, the pump would need to be disassembled.

A typical raw water pump is a flexible impeller pump. Inside the pump body is a flexible rubber impeller with several vanes squeezed down one side of the pump as it turns. This pushes out any fluid trapped between the vanes creating the flow needed to pump the fluid throughout the cooling system. The impeller is a common replacement item which generally needs to be replaced at least every year. It may need to replace it or more often, depending on how much use the boat gets. The raw water pump and its impeller can quite often be difficult to access, but the effort is worth it to ensure safe and proper engine performance. Sometimes, it may be needed to remove the entire pump to get access to the impeller.

To access the impeller, first, remove the cover plate. Then the impeller should then be visible. If there is excessive swelling, noticeable wear and/or cracks, or one or more of the impeller vanes have broken off, replace the impeller pump immediately. Also replace the impeller if the vanes are not making contact with the pump body. Impeller pumps work best when it’s run on a regular basis. If the boat has sat idle for a long time, the impeller may have lost all moisture and dried up. An impeller lacking moisture is prone to breaking up during its next use.

If vanes were missing, the impeller most likely ran dry, and it requires troubleshooting to find out why and also locate the missing vanes. Debris in the cooling system hoses can limit water flow and cause your engine to overheat. Detach all cooling system hoses and look for any pieces of rubber which might be loose. Check for a collapsed hose, a clogged strainer, a closed seacock, or any other obstruction which would prevent water from getting to the pump.

An impeller fits snug inside the pump body, and usually requires a tool and some force to pry it out. Impeller manufacturers recommend using a specially-designed impeller puller to remove it. An impeller puller is a worthwhile investment. It will avoid unnecessary damage to the pump body or other pump components with a quality impeller puller. Most impellers are a sliding fit on the pump shaft, but a few feature locking screws or retaining rings that will need to be removed as well. Very important – before removing the impeller from the pump completely, note the direction the vanes bend inside the pump housing. Then turn the new impeller so it pushes the vanes down in the same direction.

Make sure the new impeller represents an exact replacement for the pump model for the engine. Hundreds of impellers exist on the market, all with different diameters, thicknesses, shaft sizes and types, materials and so on. Some variations are slight, but they can make a huge difference. For example, many late model Volvo Penta gas engines use one of two different almost identical impellers. They differ only 1/32-inch in thickness, but this slight difference can cause the engine to overheat! To verify that it's the correct impeller for the application, get the model and the serial number of the engine. You can then email Macomb Marine Parts for help in identifying the correct impeller.

When the impeller is replaced, make sure the impeller gasket and/or o-rings are also replaced. These usually come with a new impeller. Once again, it should be an exact replacement of the gaskets or o-rings removed. Depending on the condition of the components inside the water pump, it may be needed to either replace the pump or rebuild it. Replacing the entire pump can be a much quicker repair, but a new raw water pump can cost several hundreds of dollars. Rebuilding the pump might be more cost effective, but it can take longer and requires more technical skill. Also, if it is an older pump, many internal components may no longer be available. A pump replacement may be the only option.

The internal components will vary from pump to pump. Inside the pump, there may be a cam, a wear plate, shaft seals (there are several varieties), bearings, a shaft, other retaining rings, gaskets, and seals. Removing some of these components can be tricky. If it is done wrong, significant damage to the pump and other component parts can occur. It’s recommended to seek out an experienced marine mechanic for a major pump rebuild.

Regular maintenance of a boat is the key to enjoying the fullest  time on the water. Taking the time to inspect the cooling system – and especially the engine cooling pump – will save a lot of trouble and money. It will also help to maximize the time spent having fun on the water. Visit MacombMarineParts.com today!