**12 December 2016**

Most marine engines employ salt water, commonly called raw water, as a coolant source. The raw water is pumped around the engine to cool not only the coolant  (fresh water mixed with antifreeze) that cools the engine, but also the lubricating oil and the exhaust before it is routed overboard and back to the sea.


Heat exchanger, where raw water cools the coolant.

As we sailed north from Grenada our raw water pump began leaking around the bearings after several months of faithful service, and I replaced it in Bequia with a spare pump we had rebuilt while in Grenada.  32 days ago, as we tried to get underway to head north to Martinique, our overheating saga began.

We checked out the pump and replaced both the impeller and the cover plate, and it appeared to be running as designed but we never really could determine if there was sufficient flow because our overboard exhaust discharge is underwater.  There’s good reason why many boats plumb the overboard discharge above the waterline.

With help from many sources, which was sometimes overwhelming, we traced out every inch of the raw water route looking for a blockage. Along the way I found oil leaking through the oil cooler, and some delamination in the exhaust hoses, so we replaced those. But otherwise the system seemed clear.

After sailing to Martinique with no engine and being towed to a  marina we brought a recommended mechanic onboard. We related all of our previous troubleshooting to him, translated into French, and after 30 minutes his diagnosis was: a crack in either the block or a cylinder, suggesting that we replace the engine.

After the initial shock wore off and we talked more about the symptoms, we questioned that seemingly hasty diagnosis. Carrie’s two sons, both accomplished mechanics, also questioned the diagnosis, and we set to work again to find the true cause.

With renewed vigor we traced through the entire fresh water coolant loop this time, but still didn’t find anything that would suggest a cause for our constant overheating.  We even tested the coolant temperature sensor and the temperature gauge.  Both tested good.

With Carrie’s research projecting costs of buying a new engine at $7K-$15K and sailing somewhere (Grenada? Trinidad?) to get it installed for an additional $5K-$10K, things were looking dismal.

Then we realized that if we disconnected the hose running from the Mixer (mixes exhaust with seawater) to the Muffler and directing it into a bucket, we could start up the engine for a short period and actually see the flow from the raw water pump.


Exhaust hose running from Mixer to Muffler.

We would be venting exhaust into our bedroom, but hey…

Running the engine for 30 seconds revealed no raw water flow at all, and the problem became pretty clear.  After 4 weeks of troubleshooting, we were right back where we started, at the recently rebuilt raw water pump.

By the way, our smoke detector works very well, and boy is it loud!

With some quick local research we took our spare pumps (2) in to have them rebuilt here. Five days later we installed one and ran the engine for over an hour at the correct temperature.  Success!

The following morning we left our mooring and motored back out to St. Anne to find a secure spot to anchor.  I dove on the anchor to ensure my crew that we are securely set, but even if it does drag we now have the engine to help keep us safe.

We hope to spend a quiet and stress free Christmas and New Years with our friends.  We hope that all of you have a wonderful holiday season as well.