Gas, Kerosene, Diesel-Why change oil?
Why Change Crankcase Oil?
Motor oil must perform two primary functions. It must lubricate the engine and serve as a collector
of contamination. Therefore, regular oil changes are necessary to remove oil degradation products
and oil contamination products, to minimize engine wear and deposit formation and to prevent
premature engine failure.
Oil degradation refers to destructive changes that happen to the motor oil itself. These changes
include oxidation, nitration and additive depletion.
Oxidation of the motor oil takes place in all types of engines. High temperatures, constant mixing
with blowby products and air, and particles from engine wear make an engine lubrication system a
very reactive environment that can promote oxidation. Very simply, oxidation results from the
mixing of motor oils with air at high temperatures. It has a number of effects on the motor oil. The
most apparent is thickening (viscosity increase). Oxidation also breaks down the motor oil itself and
will lead to the formation of varnish and deposits.
Nitration also occurs within internal combustion engines. It starts in the combustion chamber where
nitrogen oxides (NOx) are formed. These gases will react with the motor oil and can also cause a
thickening effect.
Additive depletion means that the additives which are used in motor oil have lost their effectiveness
and can no longer perform as intended. For example, when oxidation inhibitors are depleted, motor
oil oxidation becomes uncontrollable. When dispersant additives have suspended their limit of
contaminants, any additional contaminants will settle from the motor oil to form deposits with the
engine.
The other limiting factor to the useful life of motor oil is oil contamination. These contaminants
include combustion blowby products, liquid fuel and solid particles.
Combustion blowby products include fuel soots, fuel resins, water and unburned fuel. These
products can cause oil thickening, form deposits and corrode engine parts. They work down past the
piston into the crankcase and are generally the result of "dirty combustion". An engine used in
typical city driving with a lot of short trip, stop and go driving, seldom has a chance to warm up
thoroughly and usually operates at its lowest efficiency. The cold cylinder walls act as condensers
for the fuel soot, fuel resins, water and unburned fuels which then work their way past the pistons
into the crankcase oil. After the engine has been run long enough to become thoroughly warmed up,
it is then operating at its best efficiency which means clean combustion and minimum contamination
with combustion blowby.
Fuel dilution is the direct result of partially burned or liquid fuel entering the crankcase from piston
ring blowby or fuel system leakage. It is the result of cold starts, stop and go driving, over-rich
mixtures and dripping injector nozzles. High amounts of fuel dilution can cause a loss of oil
viscosity (thinning), a reduction of the oil film that protects bearings and pistons form rapid wear,
varnish formation, lubricant deterioration and engine deposits.
Solid particles found in motor oils would include dirt and airborne dust, engine wear metals and fuel
soot. Dirt and wear metals can be abrasive and cause wear if allowed to become excessive. Soot can
thicken the oil and reduce adequate oil flow.
As you can see, the crankcase lubricant is a collector of contaminants and must perform under harsh
conditions. Today's high quality motor oils will provide the required performance and protection.
However, if they are not changed at regular intervals, they can become overburdened with
contamination and lose their ability to lubricate. Therefore, regular oil changes are necessary to
remove oil degradation products and oil contaminants in order to minimize engine wear, deposit
formation and to prevent premature engine failure.
Oil change intervals, as well as other vehicle maintenance items should be followed as found in the
owner's manual for the type of service involved. Keep in mind that the majority of people drive
under what is considered severe service at least part of the time. Therefore, oil and filter change
intervals should be performed as found under the severe service recommendation, or according to the
oil change indicator on vehicles so equipped.
The benefits of regular oil changes and maintenance are less engine wear and deposit formation is
minimized. This relates to lower maintenance costs improved fuel economy and better engine
performance. The net overall result is longer engine life.
{from the Web}
jim
