To load or not to load...
Q
I have a Volvo 2002 engine in my Gibsea 92. During the winter period I run my engine for about 15 minutes each week in neutral in the marina. Should I run the engine in gear? Eric Thompson, by email
STU DAVIES REPLIES:
In most yacht diesels the air intake is always wide open and the ‘throttle’ is actually a governor that controls the amount of fuel injected, which controls the power output. As the load increases, the governor senses this and injects more fuel, so keeping the speed constant. Think punching into a heavy sea: as you climb the swell the note of the engine exhaust deepens and sometimes you will see a burst of black smoke from the exhaust. The revs stay the same but the engine is taking the load. By burning more fuel to take that load the engine produces more heat – and it’s at this point I can answer your question.
Lightly loaded engines such as yours running in neutral don’t produce enough heat, meaning the cylinders and exhaust system are at sub-optimal temperature leading to more harmful exhaust products being deposited in your exhaust elbow. Bore glazing and ring sticking can also become a problem.
So to answer your question, put it in gear to load the engine and run it at a brisk speed to warm it up quickly.
I also run my engine at max speed when coming to the end of a long motor sail/engine trip: it burns out any accumulated exhaust products in the exhaust system.