When a car is producing blue smoke it means oil is getting into the combustion
chamber for one reason or another and being burnt along with the normal
gasoline. This creates a blue colored smoke which is passed down the exhaust system
and then exits the car along with normal gases. A blue smoke condition is typically present
when the engine is under load and at first start up after sitting for a few
hours.
What goes wrong?
As you can imagine engine oil is present all welcome throughout the engine as it
lubricates internal parts. The
combustion chamber is the exception. This chamber must stay as oil free as
possible to help allow the fuel to burn as clean as possible. There are nine
main causes that can allow oil to enter the chamber.
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Blue Smoke Common Causes
Engine too full of oil
Engine low on oil
Cylinder head drain back holes are clogged
Valve stem seals are worn out
Broken piston oil control ring
Plugged crankcase ventilation
Overheating engine oil
Intake gasket leak (V8 and V6 only)
Excessive block to piston clearances
What's the cost?
This repair can vary from one extreme to the next for example if the engine oil
is too full the repair means letting some out to obtain the correct level should
be around $25.00 (US) go ahead and
change the oil while
you are at, if its time. If the oil drain back passages in the cylinder head are
plugged filling the valve train galley the valve covers will need to be removed and the engine
cleaned and flushed which will run about $400.00 (US). If the engine has high
mileage or extreme usage the pistons rings can be worn out meaning the engine
will need to be replaced which can run between $2500 (US) and $7000.00 (US)
depending the type of engine.
Let's get started
The easy stuff
When the engine oil level becomes very low it can cause the oil to
become overheated and lose its viscosity. When this happens the piston oil
control rings stop working because the oil is to thin and it washes by the
rings and into the combustion chamber. To fix this problem
check the engine
oil level. Also this condition can occur when the oil level is normal if the
engine is under heavy load for a long period of time. This is why some heavy
duty trucks are equipped with oil temperature gauges.
If the engine is too full it can cause the piston oil control rings to
be overloaded causing the same effect as overheated oil. Lift the hood and locate the engine oil level dipstick which usually has
a yellow handle on it to distinguish it from other components. With the
engine off and the car on level ground remove the dipstick and wipe it
clean, then reinsert and remove to observe the level. The level should be
between the FULL and ADD marks.
Engines are designs with a crankcase ventilation system of some kind to
allow internal crankcase pressures to dissipate. This system can be built into the
valve cover using an internal baffle system or the job can be done by the PCV valve (positive crank ventilation) and a breather. Both are typically
found near the top of the engine or under the intake manifold on some four
cylinders. Look for broken or disconnected hoses and remove and check the
PCV valve. Shake it back and forth to make sure it rattles lets you know it
is working.
Little tougher
Due to poor maintenance sludge can build up inside the engine's cylinder
head not allowing the lubricating oil of the valve train to drain
successfully back into the crankcase (oil pan). As a result the oil fills
the cylinder head forcing oil down the intake and exhaust valve stems (past
the seals) and into the combustion chamber or directly into the exhaust port
(fire). To check for this condition the
valve covers must be removed
for inspection. If sludge is found the drain back holes then must be cleaned
and the sludge flushed down through the oil pan and out of the engine. After the repair
it take about 2 to 4 days before the remainder of oil on the valve stems to
dry up.
Valve stem seals are designed to control the amount of oil that is
allowed to lubricate the valve stems inside the cylinder head. Both intake
and exhaust valve are equipped with these seal and when they wear or get
over heated they can allow too much oil to travel down into the combustion
chamber much like when the cylinder head drain back hole plug up. These
seals can be changed while the cylinder head is still on the car in most
cases.
The top two piston rings are design to contain the combustion of the
engine while the third ring down controls the engine oil. As an engine wears
the integrity of this seal becomes comprised allowing both combustion to
escape (blow-by) and engine oil to enter the combustion chamber. This can
typical be tested by doing a
compression test and
visually checking for oil on each of the spark plugs. It best not to replace
the piston rings due to the irregular shape of the cylinder bore, (the
problem will be worse, round ring into an oval hole). Replacement engines
can be obtained by the dealer or at a independent rebuilder, call for prices
and go with the best warranty.