Bad practice: Engine idling




A common misconception in the marine industry is that you must allow diesel engines to idle before putting them under load. With modern diesel engines, this belief is 100%, completely incorrect.

In fact, allowing an engine to sit at idle for long periods of time has the opposite effect: It increases wear on the engine, increases emissions, and wastes fuel.

How did this belief get started? Quite simply, people observed truckers at truck stops allowing their engines to idle and thought it was “Best Practice.” On older diesel engines, this may have been the case with fuel efficiency, and it is certainly the case with gasoline engines. Yet, a glance at a fuel consumption curve will show that a diesel consumes more fuel at idle, over a greater time period, than at startup. Additionally, in colder climates, it is believed that idling maintains the temperature. However, all modern diesel engines that are used in cold climates have sufficient heating to allow an easy start.

Unlike gasoline engines, modern diesel engines are designed to heat up under load. The fuel is under compression by heat, combusting more efficiently, and idling does not generate that necessary heat. Sitting at idle does not provide this load, and merely increases the friction in the cylinders. The load is generated on a boat under throttle. Idling for a period of time any more than an initial 30 seconds or so after the engine is started does nothing. No extra lubrication. No benefits. All marine engines manufactured by MarineDiesel are sufficiently lubed in this time period.

Finally, add in the fact that many jurisdictions in the world restrict unnecessary idling, due to emissions, this practice is one that should be eliminated. It just creates waste.