The severe
engine conditions of temperature and pressure to which the lubricating oil is
subjected, cause its deterioration in many ways.
Sludge formation
Sludge is a mushy material composed of oil, dirt, water and
other combustion products. It readily clogs the oil lines and galleries. It is
caused by the condensation of water in the engine crankcase, which forms an
emulsion with the oil dirt and other matter. Obviously, this occurs in the case
of the engine which seldom runs hot to drive away the water vapour out of the
crankcase.
A vehicle, which runs mostly in traffic, running slow and stopping intermittently
is thus more prone to sludge formation. This can be remedied at least partially
in the case of such a vehicle by adjusting its cooling system so that the engine
remains at a reasonably high temperature.
Lacquer formation
Lacquer or varnish is formed when the oil gets oxidized due
to high temperatures. Lacquer is often responsible for sticking valves and
clogged piston rings. To avoid this problem, use suitable additives and change the
oil regularly.
Oil dilution
Oil dilution is caused by the leakage of gasoline past the
piston into the crankcase, or by the condensation of water vapor in the
crankcase. This happens often when the engine is cold which means at the time of
starting and warming up. In winter, the choke is used frequently to start the engine.
The effect of using a choke is to introduce a small additional quantity of
gasoline in the cylinder, which contributes towards oil dilution. Thus it is
seen that choke should be applied only when it becomes a must, for example,
in very cold weather. Further, it is also observed that the dilution occurs
mostly under starting and idling conditions only. It follows; therefore, that the engine should not be raced heavily just after starting because there is no
lubrication at that time.
Oil dilution
may give sometimes a faulty dipstick reading. For example, if the dipstick shows a satisfactory oil level when put into the sump when only the engine has started,
the same will be misleading because the condensed water vapour is also present
there in the sump. As the engine warms up and comes to normal running
conditions, the water will vaporize and the indicated oil level will therefore
fall.
Carbon deposition
Carbon formation occurs normally on the combustion chamber
walls, piston, valve stems and piston rings. It results due to incomplete
combustion of fuel, particularly so at the time of starting and idling when
richer fuel is supplied.
Carbon is a
bad conductor of heat and therefore dissipation of heat from the engine will be
less. The result is higher combustion chamber temperatures, which encourage
oxidation of the oil and thicken out the deposits further. Moreover, the
tendency to detonate is increased. The sticking of rings in the grooves causes
blow-by of hot gases and the consumption of oil is increased.
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