Diesel Smoke tells YOU a Story...
Basically, smoke from a diesel
engine indicates that something is not right. It 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. It 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, that 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, it 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, under most
A short puff of smoke when an engine is accelerated under
load may be acceptable, due to the lag before the turbocharger speed and air
flow is able to match the volume of diesel injected into the cylinders. That
would only apply to older technology diesel engines, but with modern type
diesels, no smoke at all should be evident.
There are three basic types of
smoke, as identifiable by their color.
BLACK SMOKE is the most common
smoke emitted from diesel engines. It indicates poor and incomplete combustion
of the diesel fuel. There are many causes, including
- Dirty or
turbocharger (ie not enough air to match the fuel)
valve clearance Incorrect
cylinder compression (eg sticking piston rings or worn components)
- Dirty air
induction system (eg system too small or kinked inlet piping)
engine tune factors
carbon build up in combustion and exhaust spaces
Obviously, worn or
damaged components must be replaced, and the earlier you identify and fix the
problem, the less damage will be done. Keep on top of engine tune issues,
including valve adjustments, and regular servicing of air, fuel and oil filters.
Do not buy fuel from suspect outlets. Dirty components, such as injectors can
be easily restored to full cleanliness by using an effective and reliable fuel
system cleaner. If you choose from our range of products, Cleanpower is what you need.
Cleaning of internals
of engines has usually only been possible at overhaul, however, Cost Effective
Maintenance provide two products to enable vehicle and equipment owners to
quickly, safely and cheaply restore full cleanliness to combustion and exhaust
spaces (FTC Decarbonizer) as well as piston rings,
oil pumps, oil galleries, oil coolers, piston skirts, valve gear, etc (Flushing Oil Concentrate).
Black smoke is high
in carbon or soot, which is an undesirable product of diesel combustion. Now,
the combustion of diesel is a complicated process of breaking down the various
hydrocarbon fuel molecules into progressively smaller and smaller molecules, by
burning in the presence of oxygen. The main and ideal end products of
combustion are CO2 and H2O (carbon dioxide, the greenhouse gas and water). It is believed that the last step in the
process is carbon monoxide (the poisonous gas) to carbon dioxide. This is also
the slowest step by far, and when combustion conditions deteriorate some
upstream bottle necking occurs in the chain of combustion reactions. This
results (according to some authorities) in polymerization of smaller partly
burnt molecules into much larger ones, which become visible as soot, or black
BLUE SMOKE is an indication of oil being burnt. The oil can enter
the combustion chamber for several reasons.
- Worn valve guides or seals
- Wear in power assemblies (ie cylinders, piston rings,
- Cylinder glaze
- Piston ring sticking
- Incorrect grade of oil (eg oil too thin, and migrating
past the rings)
- Fuel dilution in the oil (oil thinned out with diesel)
At cold start, blue smoke is often evident, and can
reflect reduced oil control, due to fouling deposits around piston rings 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 time, but it is worth
noting, that engines with good sound compression can actually burn quite a lot
of oil without evidence of blue smoke. Good compression allows oil to burn
cleanly, as part of the fuel. It is not good though!
Once again, restore physical cleanliness to all
components. Replace worn parts where necessary. In some situations, where the
engines are pretty worn, but you just need to keep them in service, cleaning
with the previously mentioned products, followed by effective additional
anti-wear protection, will reduce internal stresses on all those tired
components, providing extended service life.
WHITE SMOKE occurs when raw diesel comes through the exhaust completely intact
and unburned. Some causes of this include
- Faulty or damaged injectors
- Incorrect injection timing (could be a worn timing gear or
damaged crankshaft keyway).
- Low cylinder compression (eg caused by leaking or broken
valves, piston ring sticking, cylinder and/or ring 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, and are often to blame. Unfortunately, expensive mechanical
repair is the only proper solution here.