Cessna 172R Operating Handbook page 236

SECTION 7
AIRPLANE SYSTEMS DESCRIPTION
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Oil pressure signals are generated from an oil pressure
line/transducer combination.
upper front of the engine
baffle, the oil
I
transducer produces an electrical signal which is translated into a
pressure reading by the oil
instrument panel.
In addition, a separate low oil pressure indication is provided
through the panel annunciator. This annunciator is wired to
pressure switch located on the rear of the engine accessory case.
When oil pressure is below 20 PSI, the switch grounds and
completes the annunciator
light. When pressure exceeds 20 PSI, the ground is removed and
the OIL PRESS annunciator goes
The low oil pressure
hour (Hobbs) meter.
PSI, a ground is supplied to the hour meter,
completing the hour meter circuit.
temperature signals
Oil
probe located in the engine accessory case. As oil temperature
changes, the probe
translated into oil
The engine driven mechanical tachometer is located on the
instrument panel to the right of the pilot's control wheel. The
instrument is calibrated in increments of 100 RPM and indicates
both engine and propeller speed. An hour meter in the lower section
of the dial records elapsed engine time in hours and tenths.
Instrument markings include the normal operating range (green arc)
from 1 900 to 2400 RPM.
The exhaust gas temperature (EGT)
LH instrument panel as part of the EGT/Fuel Flow indicator. Since
exhaust gas temperature varies with fuel-air ration (mixture), density
throttle position and
altitude,
adjusting the mixture for best economy
indicator allows
fuel-air mixture)
exhaust gas
can be positioned manually
location of the peak. Never lean using EGT when operating at
than 80% power.
more
7-20
An oil
case
pressure line is connected
circuit, illuminating
switch
are generated from a
resistance
temperature readings
the pilot to lean (reduce the
a known value using the maximum or "peak"
to
as a
temperature
pressure line is routed from the
the rear engine baffle. At the
to
to
pressure gage
out.
NOTE
is also connected
pressure exceeds
When
changes. This resistance is
on the cockpit indicator.
indicator is located on
RPM, the instrument is
or performance. The EGT
proportion of fuel in the
reference. An index
provided for the pilot
is
CESSNA
MODEL 172R
a transducer. This
located on the LH
the red OIL PRESS
to the
20
resistance-type
a useful aid in
pointer which
to mark the
Revision 7
a
the