Generator Blues, the Refrain

You’re just going to have fill in your own basic minor chord blues riff there.

The back 1/3 of the generator lying in the cockpit

When we called in the cavalry from the local Westerbeke distributor we knew there were two problems with the generator. 1) It was not making A/C power when running and 2) it was stalling out intermittently.  Ninety percent of diesel issues involving stopping are tied to fuel.  Since in my research I found a fuel filter that I previously did not know existed (and therefore had not changed in seven years) I thought I might have a line on what that second problem might be. I was wrong. The good news is the Main Stator came back rebuilt, the generator is reassembled, and when it is running it is producing AC power again.  So that part of the repair worked well. The bad news is they engine was stalling out not because of fuel problems, but because of problems relating to a failed heat exchanger.  Which I might add is every bit as hard to rhyme as “Generator”. Most larger diesel engines in boats are Fresh Water Cooled, like your car but they use a different means to cool off the liquid (or Coolant – a mix of fresh water and anti-freeze) that does the job.  Your car uses a radiator to cool this fresh water coolant.  Air passes over the flat metal blades in the radiator while coolant pumps through the baffles, the baffles radiate off the heat and cool the coolant.  As your car goes faster you get more and air flow to help this.

There are two different problems with this in a boat.  First a sailboat doesn’t go more than about ten miles per hour under power so you don’t get the same airflow.  But more importantly the engine is buried deep within the bowels of the boat which is usually a hot stifling room with little airflow.  So instead of relying on fast-moving air a “Fresh Water Cooled” boat diesel will generally use sea water to cool the Coolant in the engine.

This is accomplished with a “Heat Exchanger”.  A heat exchanger a bundle of copper pipes contained inside a tube.  Sea water passes in one direction through the small copper tubes.  Engine coolant is flushed through the heat exchanger around the smaller tubes in the other direction, bathing the small cool tubes and bleeding off heat from the coolant into the sea water which is then pumped out the exhaust.  The sea water (or “raw water” as it is known) only contacts the engine in the exchanger, the pump and the plumbing hoses.  Since raw water contains a lot of minerals, salts, and contaminants and can be corrosive this is a good thing.  There is no direct liquid contact between the Coolant, which circulates through the whole engine, and the raw water.

It appears that one or more of the small copper pipes in the heat exchanger has failed.  Sea water is getting into the freshwater coolant.  This means several things.  First, the exchanger has failed.  Some exchangers have replaceable cores, where the copper pipes can be pulled out and changed.  This does not appear to be the case in our engine.  Secondly, seawater has circulated to places it shouldn’t.  This is bad, very bad.  A very thorough flush of the cooling system must be done after replacing the exchanger to ensure any ongoing damage stops and all salt and deposits are cleared out.  Some engines do use pure raw water cooling, so it is not instantly fatal to an engine, but those engines are designed to deal with raw water.

The final implication is that some things in the engine might get damaged.  It appears the overheat sensor is one of those things.  Fortunately it is not a big expensive part, but when it senses overheating it disrupts the electrical flow needed to keep the engine running.  This part is damaged, and is likely the culprit for shutting the engine down even when it was not over heating.  The sensor needs to be replaced but the heat exchanger problem needs to be rectified first.

The good news in this is we can likely get a used replacement exchanger here in Panama for a not outrageous amount of money – a new one ordered in the states costs more than $1,200 and that is just the part, not the labor to replace it.  The bad news is we are losing more time wasting away here in Panama City.