Cessna 172N - Page 124

SECTION 7
AIRPLANE
& SYSTEMS
DESCRIPTIONS
CESSNA
MODEL
172N
ENGINE OIt SY5TEfrl
Oil
for engine
lubrication
is supplied
from a sump
on the
bottom of
the
engine. The capacity of the engine
sump is six
quarts
(one
addi-
tional
quart
is required if
a
full flow oil
filter is installed).
OiI 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
oil
filter if
installed). If
the oil is
hot,
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
(fuII
flow oil
filter, if
installed).
The
filtered
oil
then
enters a
pressure
relief
valve
which regulates
engine
oil
pres-
sure by allowing excessive
oil to
return
to
the
sump,
while
the
balance
of the
pressure
oil
is circulated to various
engine
parts for lubrication.
Residual
oil is
returned to
the sump
by
gravity
flow.
An
oil
filler
caploil
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.
To minimize
loss
of oil
through
the
breather,
fill to five
quarts
for
normal flights
of
less
than
three
hours.
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
engine
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
wiII hold
the
valve open.
After drain-
ing,
use a
suitable
tool to
snap
the valve
into
the extended
(closed)
position
and remove the drain
hose.
IGNITION-STARIER SYSTEfrT
Engine
ignition
is
provided
by
an
engine-driven
dual
magneto,
and
two
spark
plpgs
in
each cylinder.
The
right magneto
fires
the lower
right
and upper left
spark
plugs,
and
the
left magneto
fires
the lower
Ieft
and upper
right spark
plugs.
Normal
operation
is conducted
with
both magnetos
due to the more complete
burning
of
the
fuel-air
mixture
with
dual ignition.
Ignition and
starter
operation is
controlled
by
a
rotary type
switeh
located on the
left switch
and
control
panel.
The switch
is labeled
cloek-
7
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