Cessna Skyhawk 172N Pilot Operating Handbook page 124

SECTION 7
CESSNA
AIRPLANE
&
SYSTEMS DESCRIPTIONS
MODEL 172N
range of use.
It
is, however, suggested that cruising be accomplished at
65% to 75% power until a total of 50 hours has accumulated or oil
consumption has stabilized. This will ensure proper seating of the rings.
The airplane is delivered from the factory with corrosion preventive
oil in the engine.
If,
during the first 25 hours, oil must be added, use only
aviation grade straight mineral oil conforming to Specification No. MIL­
L-6082.
ENGINE OIL SYSTEM
Oil for engine lubrication is supplied from a sump on the bottom ofthe
engine. The capacity of the engine sump is six quarts (one additional quart
is required if a full flow oil filter is installed). Oil is drawn from the sump
through an oil suction strainer screen into the engine-driven oil pump.
From the pump, oil is routed to a bypass valve.
If
the oil is cold, the bypass
valve allows the oil to bypass the oil cooler and go directly from the pump
to the oil pressure screen (full flow oUfilter if installed). If the oil ishot, the
bypass valve routes the oil out of the accessory housing and into a flexible
hose leading to the oil cooler on the lower right side of the firewall.
Pressure oil from the cooler returns to the accessory housing where it
passes through the pressure strainer screen (full flow oil filter, if
installed). The filter oil then enters a pressure relief valve which regulates
engine oil pressure by allowing excessive oil to return to the sump while
the balance of the oil is circulated to various engine parts for lubrication.
Residual oil is returned to the sump by gravity flow.
An oil filler cap! oil dipstick is located at the rear of the engine near the
center. The filler cap! dipstick is accessible through an access door in the
engine cowling. The engine should not be operated on less than four quarts
of oil. For extended flight, fill to six quarts (dipstick indication only). For
engine oil grade and specifications, refer to Section 8 of this handbook.
An oil quick-drain valve is available to replace the drain plug on the
bottom of the oil sump, and provides quicker, cleaner draining of the
CUI""HI""
oil. To drain the oil with this valve, slip a hose over the end of the
valve and 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
suitable tool to snap the valve into the extended (closed) position and
remove the drain hose.
IGNITION-STARTER SYSTEM
Engine ignition is provided by an engine-driven dual magneto. and
two spark plugs in each cylinder. The right magneto fires the lower right
7-18
1 July 1978