Strange Problem With the Diesel

Last week I realized that it was time to do the 250 hour maintenance to our new diesel. We had actually gone over a few hours, but we were close. The maintenance is pretty easy and consists of changing filters, changing o-rings, change the belt, and a few other odds and ends. Doing maintenance like this gives you the chance to give the engine a good once-over for other problems. It’s a good thing I did take a closer look.

A few months ago I noticed that a bit of coolant was being pushed past the exchanger cap and was leaking into the bilge. I bought a recovery tank and installed it to catch any future overflow. During the maintenance, I noticed that coolant was being pushed out of the overflow tank’s cap at an alarming rate. I initially thought it was probably saltwater that was being pumped past a leaky heat exchanger tube, but in closing the saltwater intake seacock, the water was still coming out the overflow cap. The only other theory I had was a long shot, but I was running out of ideas.

The only other place where outside water comes close to the coolant, is inside the hot water heater where the exchanger coil has hot coolant running through it. I turned off the fresh water pump and opened the faucet in the galley to release pressure. The overflow at the take cap slowly stopped. Bingo! I found the problem! I plumbed a double-male into the coolant lines from the engine and looped the hot water heater exchanger tube back into itself. This temporary fix worked well enough so that I could complete the maintenance and could buy a new hot water heater. Maintenance complete and now off to West Marine for a new hot water heater!

I installed the new water and plumbed it to the engine, and finally finished. As it turned out, the pressure from the fresh water pump was greater than that of the coolant in the hot water heater, and so pushed fresh water into the engine and out the overflow. The maintenance was complete and the water ingress that was caused by a leaky hot water heater exchanger coil, was solved. Now, off the the next adventure!

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About Captain Tom

Over 10 years sailing and over 3500 miles under our keel. Was an engineer (EE) for over 30 years, then after moving into management, decided that the corporate world was no longer for me. Ran my wife's law office for 15 years and recently retired. Now we live aboard and sail the California coast, soon to leave for the Sea of Cortez.
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