For the complete engine maintenance story, start with the first article: Periodic Engine Maintenance and Spares.
Knowing your engine model doesn't confirm which water pump you have. It's easy to determine by simply looking at one simple characteristic.
A variety of pumps were used by the engine manufacturer
Universal Medalist used both Sherwood and Oberdorfer water pumps throughout the production of their diesel engines. After Medalist was purchased by Westerbeke, the pump was changed to a different Sherwood pump. After this change, we are told that all Universal diesels installed in Catalinas used the later Sherwood pump.
For those who enjoy learning every detail about each pump, we have posted extensive information on our site regarding engine models, years, impeller dimensions etc. Visit the pump's or the impeller's feature page and explore the information available under every available tab, Description, More Info, Dimensions, and Warnings & Notes.
Another factor adds additional confusion however. Even if you have an early boat, you may have the new Sherwood pump. As old pumps have worn out, they may have been replaced. We offer a Westerbeke upgrade kit. This kit replaces either the old Sherwood or Oberdorfer pump with a new Sherwood pump. A previous owner may very well have upgraded to this pump in the past. All this information makes it looks intimidating and confusing to determine what impeller you need.
Three machine screws fasten the cup onto the body of the pump. The heads of the screws are only accessible from behind the cup, an extremely unfortunate design choice.
Just look at the fasteners: A late Sherwood pump has three
The housing is secured to the pump with three machine screws. This is the late Sherwood pump.This pump requires Engine Spares Kit #Z2555 (for M series engines) or Impeller Kit #Z2545.
The Oberdorfer's design provides for much quicker access to the impeller. Its four machine screws are easily accessible.
The Oberdorfer pump has a simple square cover plate with four fasteners
Notice the cover plate is secured to the pump with four screws on the Oberdorfer pump. Any Oberdorfer pump uses our Engine Spares Kit #Z2553 (for M series engines) or impeller kit #Z2548.
A simple round cover plate with easy to access machine screws are a feature of this early pump.
Early Sherwood pumps used six fasteners
The cover plate of the early Sherwood is secured with six screws. This pump requires Engine Spares Kit #Z2554 (for M series engines) or impeller kit #Z2549.
If your early Sherwood pump is leaking, it will need to be replaced. If it has the typical 3/8" female National Pipe Thread (NPT) ports, the correct replacement pump can be located here: Z2857