Cessna 1973 172 - Oil Quick-Drain Valve; Carburetor Air Temperature Gage

OIL QUICK-DRAIN VALVE
An oil quick-drain valve is optionally offered to replace the drain
plug in the oil sump drain port. The valve provides a quicker and clean-
er method of draining engine oil. To drain the oil with this valve in-
stalled, slip a hose over the end of the valve, route the hose to a suitable
container, then push upward on the end of the valve until it snaps into the
open position. Spring clips will hold the valve open. After draining, use
a screwdriver or suitable tool to snap the valve into the extended (closed)
position and remove the drain hose.
CARBURETOR AIR TEMPERATURE GAGE
A carburetor air temperature gage may be installed in the aircraft to
help detect carburetor icing conditions. The gage is marked with a yel-
low arc between -15° and +5°C. The yellow arc indicates the carburetor
temperature range where carburetor icing can occur; a placard on the
gage reads KEEP NEEDLE OUT OF YELLOW ARC DURING POSSIBLE
ICING CONDITIONS.
Visible moisture or high humidity can cause carburetor ice formation,
especially in idle or low power conditions. Under cruising conditions, the
formation of ice is usually slow, providing time to detect the loss of RPM
caused by the ice. Carburetor icing during take-off is rare since the full-
open throttle condition is less susceptible to ice obstruction.
If the carburetor air temperature gage needle moves into the yellow
arc during potential carburetor icing conditions, or there is an unex-
plained drop in RPM, apply full carburetor heat. Upon regaining the
original RPM (with heat off), determine by trial and error the minimum
amount of carburetor heat required for ice-free operation.
NOTE
Carburetor heat should not be applied during take-off
unless absolutely necessary to obtain smooth engine
acceleration (usually in sub-zero temperatures).
7-8
1