Cessna Skyhawk 172N Pilot Operating Handbook page 123

CESSNA
SECTION 7
MODEL 172N
AIRPLANE
&
SYSTEMS DESCRIPTIONS
ENGINE INSTRUMENTS
Engine operation is monitored by the following instruments: oil
pressure gage, oil temperature gage, and a tachometer. An economy
mixture (EGT) indicator and a carburetor air temperature gage are also
available.
The oil pressure gage, located on the left side of the instrument panel,
is operated by oil pressure. A direct pressure oil line from the engine
delivers oil at engine operating pressure to the oil pressure gage. Gage
markings indicate that minimum idling pressure is 25 PSI (red line), the
normal operating range is 60 to 90 PSI (green arc), and maximum pressure
is 100 PSI (red line).
Oil temperature is indicated by a gage adjacent to the oil pressure
gage. The gage is operated by an electrical-resistance type temperature
sensor which receives power from the airplane electrical system. Oil
temperature limitations are the normal operating range (green arc) which
is 100°F (38°C) to 245°F (H8°C), and the maximum (red line) which is 245°F
(118°C).
The engine-driven mechanical tachometer is located on the instrument
panel to the left 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 (multiple width green arc) of 2100 to 2700 RPM, and a maximum (red
line) of 2700 RPM. The multiple width green arc has steps at 2450 RPM, 2575
RPM, and 2700 RPM which indicate a 75% engine power setting at altitudes
of sea level, 5000 feet. and 10,000 feet.
An economy mixture (EGT) indicator is available for the airplane, and
is located on the right side of the instrument paneL A thermocouple probe
in the tailpipe measures exhaust gas temperature and transmits it to the
indicator. The indicator serves as a visual aid to the pilot in adjusting
cruise mixture. Exhaust gas temperature varies with fuel-to-air ratio,
power, and RPM. However, the difference between the peak EGT and the
EGT at the cruise mixture setting is essentially constant, and this provides
a useful leaning aid. The indicator is equipped with a manually positioned
reference pointer.
A carburetor air temperature gage is available for the airplane. Details
of this gage are presented in Section 9, Supplements.
NEW ENGINE BREAK-IN AND OPERATION
The engine underwent a run-in at the factory and is ready for the full
1 July 1978
7-17