Changing the raw water pump impeller on a Kohler 5E marine generator is really a breeze as long as it can fit in the small work area where the pump is. The generator is a closed system with a heat exchanger mounted on top of the generator. You will only need a few hand tools to do this job. A new booster is available at your marina or local marine supply store.
You must first turn off the raw water supply at the helmet accessory. Locate the pump, mine is mounted on the starboard side of the boat, even with the waterline yours could be on the opposite side. Remove the four 1/4 “bolts that hold the pump to the generator. The only thing you really need to remove from the pump is the cover with the O-ring and then remove the old impeller from the pump. Pump partially off the driveshaft and then snap back into position so the impeller sticks out a bit so you can grab it with your pliers.
If you have most of the impeller vanes on the old impeller, there is no need to worry. If there are only a couple of impeller vanes on the old impeller, it is a good idea to flush the system with a garden hose to make sure there is good water flow and most of the vanes are out of the system. Check the rotation of the pump by tapping the start button on the generator control panel and note which direction the shaft has moved or if the impeller still has vanes install the new impeller with the vanes running in the same direction.
The next thing you need to do is install the impeller on the pump. You should lubricate the impeller with petroleum jelly or liquid soap to facilitate installation and start-up. The easiest way to fit the impeller into the pump is to pull the pump out of the generator a bit, place the impeller on top of the pump, and rotate it in the correct direction to start (the vane tips follow the rotation), and then align the impeller with the flats on the driveshaft and slide it into the pump body. After installing the impeller, the O-ring should be put into the groove of the pump casing with a little lubricant, and the cover should be replaced with the bolts and tightened.
When the cap is in place and tight, it is time to open the water intake valve, checking that there are no leaks. After everything looks good, it’s time to run the generator to make sure the entire system is working properly. There should be an ample supply of water coming from the generator exhaust port while the generator is running. This will become a normal annual maintenance job on your boat with normal use of the generator.
Sometimes these boosters will last a few years with just periodic use, but most will need to be changed annually if they are used frequently during boating season. Different makes of boats will have the same type of system and are very close to this procedure. The only major difference could be the pump that is used in the generator, but it still shouldn’t be a large pump.
After performing this maintenance item for the first time and getting to know your boat, it should only take about 20 minutes to complete this task. The first time can be up to 90 minutes or so depending on what you will study, concentrate, and observe.
This procedure was performed on a 2006 Searay, 280DA with twin 5.0 Mercruiser engines.
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