Page 159 - 05. Subyek Teknik Mesin - Automobile Mechanical and Electrical Systems Automotive Technology Vehicle Maintenance and Repair (Vehicle Maintenance Repr Nv2) by Tom Denton

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Engine systems 143

Figure 2.124 Gauge and circuit: 1, voltage stabilizer; 2, gauge; 3, sender unit

to the cooling-system radiator at the front of the vehicle. Pipes from the fi lter
housing carry oil to and from the oil-cooler radiator.
A key component of the lubrication system is the dipstick. No matter how clever
the system is it will not work if the oil level is low. The dipstick is marked to show
the maximum and minimum acceptable levels. Key fact
Many modern engines are now also fi tted with an electronic sensor that A key component of the lubrication
system is the dipstick!
supplies information to the driver on the level of oil in the engine (low oil pressure
indicating low oil level). A warning light, or a gauge in the instrument panel,
indicates whether the oil level is within acceptable levels ( Fig. 2.124 ). The sensor

is fi tted into the sump or the engine block. Some engines now have oil quality
sensors to indicate when the oil should be changed.
To warn the driver about low oil pressure, a pressure-sensitive switch is fi tted
into the main gallery. It makes an electrical contact when the pressure is below
about 0.5 bar (7 psi). The switch may be fi tted in the same circuit as the oil level
warning lamp. When the switch contacts make a connection, the lamp lights,
and this should occur before the engine is started. Once the engine is running,
oil pressure builds up and the switch contacts separate and the warning lamp
will go out. This indicates that a minimum oil pressure is being maintained in the
system. Oil pressure gauges are also used and employ a piezoelectric pressure
sensor fi tted into the main gallery and a gauge unit.

2.2.4 Oil fi lters

Even new engines can contain very small particles of metal left over from the
manufacturing process or grains of sand that have not been removed from the
crankcase after casting. Old engines continually deposit tiny bits of metal worn
from highly loaded components such as the piston rings. To prevent any of these
lodging in bearings or blocking oil ways, the oil is fi ltered ( Fig. 2.125 ).
The primary fi lter is a wire mesh strainer that stops particles of dirt or swarf from
entering the oil pump. This is normally on the end of the oil pick-up pipe. An