Changing the Impeller

White Pepper continues to be plagued with motor overheating. The motor overheated in the Northwest Providence Channel after leaving Port Lucaya. In Nassau I found that the raw water strainer was full of grass and the belt to the water pump loose. Both were easily fixed.

Then between Black Point and Cave Cay on the bank side the water belt broke. I had to replace it underway. Jan did a fine job hand steering while I wrestled the belts down below.

However, the engine continued to run hot. I suspected the impeller because little water was coming out of the exhaust. The impeller had not been changed in several years, but I had spares and gaskets for the pump thanks to the foresight of home town mechanic Don Gallant. He assured me that I would need them someday.

At first I could not even figure out how to get to the water pump. A review of a helpful blog post on the internet showed me a clever way to remove the belt and detach the whole pump from the engine. With the plate exposed the 6 bolts came right out without protest. The pump is a super simple apparatus. I was grateful that Yanmar used the highest quality materials to manufacture it. There was not a speck of corrosion despite continual exposure to salt water for decades. One curiosity was that the entire engine is metric; however, the water pump has English measure bolts—9/32 inches.

When I removed the impeller it seemed to be in good shape. One of the vanes was pointed in the wrong direction and I wondered how it survived all these years and how much that had degraded the performance of the pump. While the rubber vanes all seemed to be intact close inspection of the key way showed subtle signs of wear. I wondered if the key was slipping past the key way. (Picture below.)

I applied plenty of white lithium grease to the new impeller. I used an electrical tie to compress the vanes and line them all up in the proper direction. I had taken a picture of the old impeller to learn and remember the proper direction. I rechecked that picture and sure enough I had put the impeller in wrong. I flipped it around and eased off the electrical tie. (Picture below.) The whole thing went back together fairly easily and without leaks. The secret to avoiding leaks is to use a proper gasket which should also be heavily greased.

I opened up the sea cock and started the engine. More water seemed to be coming out of the exhaust so I know the new impeller helped. However, I suspect more problems for the future. A common problem in the Yanmar 3-HM is a plugged up mixing elbow. Or the water jacket could be full of corrosion.

Later while in St. Augustine, FL in May the real culprit was discovered by mechanic, Al.  The cover plate had become so scored that it was allowing the prime to fail.  Al simply reversed the cover, and it worked fine.  I had never heard of such a problem, but Al said it was common.

Regardless, White Pepper just needs to get back to Florida where a new engine awaits her.

Water Pump with new belt is in lower left corner.  It has to be unbolted and removed to access the impeller.

New impeller  (top) and old one with rounded key way (bottom).  By coincidence real culprit is in left upper corner.

New impeller with vanes all held in place by electrical tie.