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Why is my engine smoking?


There are usually 3 common types of smoke emitted from a diesel engine .. black, blue and white.

Basically, smoke from a diesel engine indicates that something is not right. Smoke should be taken as an indication that there is a problem existing (or developing) that will potentially shorten the engine life, or result in unnecessary costs.

Smoke should be regarded as an opportunity to take measures that will save you money in both the long term and also the short term. At the least, smoke may be due to a simple problem, that is causing poor combustion efficiency and costing you in excessive fuel bills (eg carboned up engine from excessive idling, stop start operation or short run times). At the other end of the scale, smoke may be your last chance to act before a catastrophic engine failure occurs (eg piston seizure, valve or turbocharger failure).

A diesel engine in good condition should produce no visible smoke from the exhaust, unless under heavy load. A short puff of smoke when an engine is accelerated under load may be acceptable, due to the lag before the air flow is able to match the volume of diesel injected into the cylinders.

BLACK smoke ..

A black, steady stram of smoke is the most common emitted from diesel engines and indicates incomplete combustion of the fuel. Black smoke causes can vary widely and include ..

Dirty or restricted air cleaner systems .. air filter clogged or partially blocked. Clogged or restricted muffler (actually more common than you might think).

Dirty or worn fuel injectors .. commonly carbon deposits affecting spray pattern.

Engine overloaded .. reduce load, use lower gear, 
Fuel injection pump wear, or incorrect settings.
Carbon deposits in combustion chambers .. common in lightly loaded engines.
Excessive carbon build-up around exhaust valves and exhaust spaces.
Sticking piston rings .. often due to carbon deposits.
Glazed cylinder cross-hatch .. due to carbon deposits.
Incorrect valve clearances ..
Faulty valve stem seals .. rarely.
Engine wear in general .. often misdiagnosed when carbon deposits are the real problem.
Engine oil viscosity too low .. check oil grade against operating conditions.
Incorrect fuel injection timing ... only applicable if it has been changed from its factory setting. Yanmar engines do not "loose timing". 
Poor quality fuel.

Obviously, worn or damaged components must be replaced .. the earlier you identify and fix the problem, the less damage will be done. Keep on top of engine tune issues, including valve adjustments, regular servicing of air, fuel and oil filters. Do not buy fuel from suspect outlets. Dirty engine components, such as fuel injectors can be easily restored to full cleanliness by using an effective and reliable fuel system cleaner.


BLUE smoke ..

Blue tinted smoke or smoke that has a 'burning rubber' smell is caused by engine lubricating oil burning. The oil can enter the combustion chamber from several sources including ..

Worn valve guides, or seals
Cylinder &/or piston ring wear
Cylinder glaze
Piston ring sticking
Incorrect grade of oil .. too thin and getting past rings, or valves guides
Fuel dilution of the oil, making it too thin.
Blue smoke is often evident at cold start, which can reflect reduced oil control due to carbon fouling deposits around the piston rings and/or cylinder glaze (which is actually carbon deposited in the machined cylinder crosshatching. These tiny grooves actually hold a film of oil, which in turn completes the seal between the combustion chamber and the oil wetted crankcase).

Blue smoke should not be evident at any stage.

An engine may burn oil without the evidence of blue smoke, because good compression burns oil quite cleanly, however, it is not acceptable for any new engine, or engine in good internal condition to burn large amounts of lubricating oil.

Once again, restore physical cleanliness to all components. Replace worn parts where necessary. 


WHITE smoke ..

White smoke is caused by raw, unburnt fuel passing into the exhaust stream or water burning in the combustion. Common causes include ..

Blown head gasket allowing water to enter the combustion area. This will usually smell slightly sweet. Defective fuel injectors
Low cylinder compression
Low cylinder compression may be caused by leaking valves, sticking piston rings, ring wear, cylinder wear, or cylinder glaze.

When white smoke occurs at cold start and then disappears as the engine warms up, the most common causes are fouling deposits around piston rings and/or cylinder glazing.

Water entering combustion spaces will also create white smoke. Faulty head gaskets and cracked cylinder heads or blocks are a common cause of water entry.


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Article details
Article ID: 60
Category: Knowledgebase
Date added: 2011-03-21 08:55:55
Views: 70449
Rating (Votes): Article rated 4.9/5.0 (63)

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