Ding Dong the Gremlin Is Dead!

I’ve been unusually silent, not posting updates, during our travels south.  Frustration silenced my desire to post updates.  During our first day out, Beaufort to Wrightsville Beach, we discovered that our engine was running hot.   If we ran the engine over 2200 RPM it would overheat.  Our typical operating range is 2200 to 2400 RPM.  The issue was particularly irritating due to the energy I put into engine repairs and maintenance during our summer haul out.

 So began my search for the engine gremlin causing the overheating.  Each evening, I worked to eliminate possible causes... blockage in the raw water intake; failing impeller; blockage in the heat exchanger;  low coolant level.  After a few days I exhausted possible suspects and then called Stan at Beta Marine.  Stan proved amazingly helpful and willing to assist me with the overheating.  I lowered the hot water bypass lines; filled the coolant from the high point in the system; restricted flow to the hot water tank; checked the orientation of the heat exchanger tube stack, etc.  None of these experiments proved fruitful.  According to Stan this left only two possible causes… the thermostat is functioning partially or the heat exchanger tube stack is damaged. 

We purchased a new thermostat and a refurbished tube stack.  Stan sent the parts ahead to the Fort Pierce City Marina and we picked them up upon our arrival days later.  The second I inspected the new tube stack I knew we snared the engine gremlin.  

One of these things is not like the other...

For those of you unfamiliar with a marine engine a quick explanation of the heat exchanger and tube stack I’ll do my best to pen a simple explanation.   If you are familiar with the system feel free to skip the next paragraph.

 Most marine engines intended for use in salt water circulate cool salt water through a heat exchanger and back out of the boat via the engine exhaust.   The fresh water that circulates through the engine block is cooled by the salt water in the heat exchanger, but the two fluids do not mix.  The salt water passes through small tubes in the heat exchanger tube stack (see image).  The engine coolant flows around the cool salt water filled tubes, transfer’s the heat to cool salt water, and then returns to the engine block.

The Beta Marine engine’s use a metal shield around the tube stack to direct the hot coolant around the cool water in the tubes.  In the image the hot water flows into the heat exchanger and floods around the tube stack.  The water then flows along the stack directed by the copper casing and exits the opening at the lower end.  Our old tube stack, on the right in the image, was damaged when the mechanic removed it during our maintenance this summer.  It is obvious that the shield slid down the tube and would not allow the coolant water to exit and return to the engine block.  I am surprised the mechanic did not realize this would cause over heating once it was re-installed.

Ding dong the gremlin is dead!