Buddy,
The Sherwood pump will work. But there really is no reason to stick with it now that the new Oberdorf is a drop in replacement.
What most of us found with the Sherwood is that the pump began to fail around 500-600 hours. You can see that by oil and/or water coming out of the "weep" hole on the lower portion of the pump housing. When that happens it's time to either rebuild the pump to replace it. I attached a photo of my old Sherwood at the time I purchased my boat. H
ere is an article from Maine Sail's site about rebuilding a water pump.
It's at that point that I started to research the pump. I found that rebuilt Sherwood pumps fail after about 200-400 hours. So rebuilding didn't seem like the best option. Purchasing a new pump seemed better. Then I looked into the quality of the pump and found that the Oberdorf was better quality, lasted longer and had better results following a rebuild. I went with the Oberdorf even though I had to get out the angle grinder and modify the base for it to fit on the engine. You don't have to do that with the new pump it drops right in.
The Oberdorf has the added benefit of being quicker to change. You can't get a socket or even a ratcheting box wrench on the bolts to remove the face of the Sherwood. This leaves you with having a small turn on an open-ended wrench and it takes you about 20-30 minutes to change the impeller in calm conditions. Now trying doing that when you have something stuck in the pump or your impeller breaks while in a busy area or on a lee shore.
You can see what the previous owner of my boat believes to be the original impeller when I first changed it. It would have been 10 years old with 500 hours on it at that time.
As far as when to replace the impeller, I adopted Maine Sail's approach to this matter. In the fall when I winterize the motor, I remove the impeller so it is not sitting in the antifreeze as that can have negative effects on the impeller material. I save that impeller I just removed as a spare after washing it with water. In the spring I put a new impeller in at launch. I keep the old one as a spare for that season and toss it in the fall when I repeat the procedure.
When we start to cruise this fall I decided I will make the impeller an inspect at 50 hrs, replace at 150 hrs item. Some may think that is too often but I would rather be safe than sorry.
Good luck and fair winds,
Jesse
