When we put Sinbad to bed on the hard last fall it had a nice dry bilge. This spring I found just a little engine coolant under our 80 horse Ford Lehman engine. I found the guilty hose right away but continued to inspect the entire system. That's when I discovered that a weld on one of the heat exchangers (think radiator) mounting bracket was broken. Not a fun job getting the two pieces off the boat to have them welded up. These surprise "jobs" quit being fun along time ago.
If you double click on the first picture it will enlarge, making it easy to see that some of the tubes are plugged. The second picture is after I pulled the end caps and ran a rod through the tubes. The pile of stones in front of the heat exchanger was what was making the rattle sound. It’s all that remains of a 30 yr old zinc pencil. The zinc is supposed to look like the one in the shiny brass base on the left side of the photo. Zincs are installed to protect the engine from electrolysis in salt water; they don't work in fresh water. I just happened to have the new one because it was on my "to do" list before heading into salt water.
In the long run this was "Good Luck". It saved me from trying to figure out why the engine was over heating when we go through the