The heat exchanger is on the upper back (aft) portion of the engine -it looks like a 4" cylinder approx. 2ft. long lying on its side athwartship. Look in your owner’s manual at the picture of an M25/M25XP it will show the exchanger and the zinc . If you don't have a manual, contact your Westerbeke dealer. That owner’s manual and the parts manual are a MUST to have on board.
The heat exchanger zinc is accessed by means of a screwed-in mount at the bottom of the heat exchanger, in the back of the engine. You'll need to access this through the back cabin; it's quite a contortion, though, so get somebody to help you if you have back problems. Ron Hill, APACHE #788
What's involved in maintaining it?
I've added this maintenance to my annual spring fitting out list, doing all that is mentioned below. One additional step that I perform is to use radiator flush (the typical automotive type - found just about anywhere) and after the cleaning ritual below, fill the exchanger with the prescribed mixture and let it soak overnight. A couple of vigorous shakes the next day, followed by multiple rinses and reassembly has kept mine troublefree for 5 years now. Several years ago I also cleaned the exterior with a wire brush and got it completely down to bare metal. Then I primed and painted it with an engine enamel (black). Bob Mack, Upon A Star #52
What size zinc do I need?
Better chandleries, especially marine diesel shops such as Hansen Marine (a Universal "stocking dealer") can tell you which zinc you need. They need to know the diameter of the heat exchanger. Some older engines have 2" exchangers the new ones are 3" in diameter. Alby Anderson, Full Moon #1380
There are two sizes (diameter) of heat exchanger zincs. You can't mix them up because the larger won't fit. But you can screw up the tubes inside the heat exchanger if the zinc is too long. Take a screwdriver, a #2 pencil, or something that will go up through the hole, and measure how far up it went. Then hack saw the zinc off to match. In high-saline conditions or year around use, I'd check the heat exchanger zinc at least twice a year. Zincs are cheap; heat exchangers and engines are expensive. Ron Hill, APACHE #788