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Smoke Signals – What Smoke from Your Diesel Generator Is Trying to Tell You

All marine diesel engines create smoke.  But it should be virtually invisible in an otherwise healthy engine.  If you do see smoke, though, you can learn a lot simply from the color of the smoke.  The following is not intended to replace the diagnosis of a registered technician.  It should, however, give you a guide to the health of your generator set’s diesel engine.


Blue Smoke


What It Means – Oil is present in the combustion chamber or is leaking into the exhaust turbocharger.


What To Do– Oil consumption will be high, but the generator may continue to run surprisingly well.  Schedule a service call.


Grey/White Smoke


What It Means – Grey or white smoke can be caused by a number of factors: Operating temperature too low for proper combustion; low compression; bad fuel which can damage the valves and injectors; worn or poorly adjusted valves; problems with the fuel injector(s); a leaking aftercooler or head gasket.


What To Do – If the smoke continues after warm up you can eliminate operating temperature as a cause.  If the diesel fuel in the engine is dirty you’ll have to flush the fuel system thoroughly.  If valves, injector or an aftercooler is compromised; or if the engine compression is low, call for service immediately.


Black Smoke


What It Means – More fuel is being delivered than can be efficiency burned, which leads to unburned or partially burned fuel in the engine.  This may indicative of a clogged or wet air intake, carbon plugged wet exhaust elbow, overloading or bad injectors.


What To Do – Contact your servicing dealer right away.




What It Means – Steam sometimes resembles white smoke but evaporates quickly. It usually signals an overheated engine.  It may also indicate a failing seawater pump or plugged sea strainer.


What To Do – Check the exhaust temp and look for problems in the cooling system.  The muffler and wet exhaust system hoses should not be hot to the touch in normal operation.  If the exhaust and cooling systems check out okay, check the seawater pump and sea strainer.  Clean or replace as necessary.


Soot on the Transom


What It Means – Soot on the transom can be a sign of excessive light load operation.  It can also indicate that the air filter is plugged, that there is an issue with the injectors, or that the propeller is not matched.


What To Do – The generator should be run at 40-50% of its rated kW load at all times to prevent underloading.  Air filters can be cleaned or replaced.  Issues with the injector or propeller should be addressed by an authorized servicing dealer.


We hope these tips were helpful.  Northern Lights is already ready to help.  You can contact our Service Department at service@northern-lights.com or by calling 1-800-762-0165.

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