For what it's worth, I've just solved a mystery related to disappearing coolant. My 34MKii engine was losing small amounts of coolant every time I checked, even though I only ever use the engine for getting to and from the marina, raising and lowering sails, and anchoring.
There were no signs of leaks on any of the engine hoses. To check to see if perhaps it was evaporating, I put pieces of cardboard down at the bottom of the engine compartment, on both sides and under the belts, then ran the engine. Again, no sign of leaks. I also ran the engine with the coolant cap off to see whether there were bubbles, an indication of a blown gasket. Nothing there, either. And no, there was no spillage coming from the overflow in the lazarette.
I cleaned the bilge completely, and then ran the engine again. This time I noticed coolant in the aft bilge compartment, but at that point there wasn't enough to leak through the passage hole to the middle part of the bilge. I couldn't see any signs of the coolant on the curved hull leading down to the bilge, so I put my hand through to feel for any coolant. When I did that I was very surprised (to say the least) that the whole top of my arm became coated with the coolant. I then looked under the galley sink and found where the coolant hose runs through to the water heater. But again, there wasn't any sign of coolant, that is until I felt around to the back of the hose.
It turned out that the hose had developed a very small hole at the edge of the tube running from the water heater. It had been seeping from that hole around the back of the hose and down to where the hose goes through the bottom of the galley sink cabinet. It then ran along the whole length of that piece of laminate until it came to the edge, and then dripped directly down into the bilge.
Needless to say, I was quite relieved, particularly since the worst case option would probably have been a leaking heat exchanger, which would have required a rebuild. All that was required was cutting a larger hole in the back of the cabinet to make it easy to get at the hose, the cutting off of the damaged part of the hose, and resetting with a hose clamp.
There were no signs of leaks on any of the engine hoses. To check to see if perhaps it was evaporating, I put pieces of cardboard down at the bottom of the engine compartment, on both sides and under the belts, then ran the engine. Again, no sign of leaks. I also ran the engine with the coolant cap off to see whether there were bubbles, an indication of a blown gasket. Nothing there, either. And no, there was no spillage coming from the overflow in the lazarette.
I cleaned the bilge completely, and then ran the engine again. This time I noticed coolant in the aft bilge compartment, but at that point there wasn't enough to leak through the passage hole to the middle part of the bilge. I couldn't see any signs of the coolant on the curved hull leading down to the bilge, so I put my hand through to feel for any coolant. When I did that I was very surprised (to say the least) that the whole top of my arm became coated with the coolant. I then looked under the galley sink and found where the coolant hose runs through to the water heater. But again, there wasn't any sign of coolant, that is until I felt around to the back of the hose.
It turned out that the hose had developed a very small hole at the edge of the tube running from the water heater. It had been seeping from that hole around the back of the hose and down to where the hose goes through the bottom of the galley sink cabinet. It then ran along the whole length of that piece of laminate until it came to the edge, and then dripped directly down into the bilge.
Needless to say, I was quite relieved, particularly since the worst case option would probably have been a leaking heat exchanger, which would have required a rebuild. All that was required was cutting a larger hole in the back of the cabinet to make it easy to get at the hose, the cutting off of the damaged part of the hose, and resetting with a hose clamp.