Systems+Engines

Ask Sail: Smoking Like a Hippie

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"Rocket" Rod Linder of Searcy, Arizona, asks:

Can you give me some ideas on what might cause excessive white smoke in the exhaust of a 2-year-old Yanmar diesel? I have added stabilizer to the tank, and the engine runs great, but it smokes like a hippie on holiday. Something is not right, and I’m not sure how to diagnose the problem.

Nigel Calder replies:

If the white smoke appears on start-up and then clears, it generally indicates poor compression in one or more cylinders. However, it seems your smoke is not dissipating, which means you may have a cylinder that is continuously misfiring. Hold your hand over the exhaust for a few seconds, and then sniff your hand. If it stinks of diesel, you have a misfiring cylinder. If not, the white smoke is probably water vapor. In this case you should check the raw-water flow (inlet, strainer, pump impeller, heat exchanger and the water-injection point into the exhaust) for loss of flow and/or obstructions. You may have enough flow to keep the engine from overheating, but not enough to keep much of the cooling water from being expelled as steam. If this doesn’t produce any clues, next check your fuel filters for dirt and water (you should really do this anyway), and if necessary clean the fuel tank. Finally, you might have a blown cylinder-head gasket or a cracked cylinder head, although given that the engine is running fine this is unlikely.

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