Hi, Just purchased a 1987 Catalina 36 in April. Two questions: I have a Universal 25XP diesel engine. The previous owner left me a small box of "spares". Included in this box were two Zinc pencils. I know that the Heat Exchanger has a Zinc Pencil that has to be changed periodically, but the ones he left me are the wrong size for the HE. Is there one anywhere else in the engine? My engine has a factory-installed or directed By-Pass that shunts the coolant thru the Hot Water Heater before it goes through the Heat Exchanger - if the gate valve on the By-Pass is closed. Seems like a good idea to me, but what would be the purpose or advantage of opening the valve? Thanks!