Hi Mark & SlackwaterJack (Alex),
Alex got me thinking more about this, so I dug out my copy of Nigel Calder's "Marine Diesel Engines, Maintenance, Troubleshooting, and Repair, Second Edition". If fellow Tugnut's don't own a copy of this book, go find one. Nigel Calder, if you don't know, is the guru of diesel mechanics and does a great job of relaying his vast knowledge in the field in a way that the average person can fully comprehend.
Anyway, In the section on troubleshooting, under "Failure to Start" on page 57, this is what Nigel has to say about the solenoid valve "Many newer newer engines have a solenoid operated fuel shutdown valve which is held in the closed position by a spring when the ignition is turned off. When the ignition is turned on, it energizes a magnet, which opens the valve. Any time the electrical supply to the solenoid is interrupted, the magnet is de-energized and the spring closes the valve. Any failure in the electrical system will automatically shut off the fuel supply to the engine."
So the electrical gremlins could still be the suspect in a potential fuel system issue, but that doesn't answer your cooling system mystery.
It just might be time to have a qualified mechanic check over the both the electrical system and the motor, it seems like this is getting rather complicated.
Eric