I love the easy engine access our Hunter 376 provides. I really feel sorry for some of the folks whose blogs I read, when they post pictures of the cramped little holes they have to crawl into in order to service their engine. But there’s one routine task we have to perform that’s a real PITA, and that’s changing the raw water impeller. On our last boat, the raw water pump was a belt driven unit that was mounted right on the front of the engine and was totally easy to access.  But on Eagle Too, the raw water pump is gear driven and set into the engine block on the port side of the engine, tight up against the bulkhead. For reasons known only to a handful of Japanese engineers, the cover plate for the impeller faces aft, right in front of the starter. There isn’t enough room between the pump cover and the starter to use a socket wrench, and the location is almost impossible to get a visual on. You have to use a box wrench to remove the four bolts that hold the impeller cover on and pull the impeller entirely by feel. I actually can’t even get my hand into the space without first removing the alternator to open up an access. It just seems like a really bad design for something that has to be serviced pretty regularly. Some people actually cut a hole through the bulkhead and install a hatch in the head (bathroom) in order to have another way to approach this problem. We just didn’t want to cut a hole in the boat for a job that’s only done once a year.

Alternator removed to give me access to the area indicated.

This is the small space you have to work in. Raw water pump to the left, starter to the right.

One thing I did discover though is that having the right tool makes the job quite a bit easier. In this case, the right tool is a pair of right-angle pliers. The first time I tried changing the impeller, it stubbornly refused to come out. I had to use the old trick of prying at it with two screwdrivers to try and get it out of the pump body, ripping it to shreds in the process. One thing I did to make the next time go a little easier is that I coated the pump shaft with Tef-Gel before installing the new impeller. This Teflon based paste keeps parts from corroding and freezing together, and it’s very useful whenever you have to put something together that you hope to be able to easily disassemble again in the future.

The other trick was the pliers. Since there’s very little room to work, I thought the perfect solution would be to use a set of right-angle pliers to reach into the pump body, grasp the impeller, and then pull it out. A quick trip to Harbor Freight turned up exactly what I was looking for.

The owner’s manual for our Yanmar 3JH2E diesel engine says the impeller should be changed every 600 hours. After we returned from our last season of cruising, we were right at 650 hours, so it was due. While the job was still a bit of a pain, the combination of having used Tef-Gel when installing the impeller and using the special pliers to get into the tight space made the job go much easier.

It looks like the recommended maintenance interval was spot on, because when I examined the old impeller, I could see the beginnings of cracks on some of the vanes. Let this job go for too long, and these vanes start breaking off, travel through your cooling system and end up clogging the tubes in your heat exchanger, causing your engine to overheat.

Vanes just starting to crack.

If you’ve done this job, you know what a pain it is. Try the Tef-Gel and bent pliers. I think you’ll be pleased with how much easier things are.

If you haven’t done this job, what are you waiting for? Don’t let a worn our impeller leave you stranded.