Oil Cooler
A fully automatic oil cooler transfers the oil
heat to cold fuel passing through the cooler.
The oil cooler is a liquid-to-liquid heat ex-
changer mounted on the oil tank mounting flange
and against the right side of the oil tank. It con-
sists of numerous longitudinal passages arranged
in a honeycomb pattern. Both fuel and oil flow
simultaneously through adjoining passages,
and an exchange of heat occurs between hot
engine oil and cool fuel. Oil enters and leaves
the cooler through ports located in the housing
for the pressure bypass valve.
The bypass valve provides protection against high
pressure due to oil viscosity or cooler blockage.
Oil Filter
The oil filter assembly is mounted in the pump
housing. It is a full-flow, in-line filter with a
corrosion-resistant screen element of corru-
gated steel. The filter filters out oil contami-
nants over 40 microns in size and is removable
for cleaning. A filter bypass valve is included
in the core of the filter element. If the pres-
sure difference between oil entering the filter
and oil leaving the filter exceeds 20–24 psi,
the valve opens to permit a direct flow of oil
through the unit without filtration.
Indication
Oil pressure is sensed by an AC transmitter and
sent to a dual-needle gage on the instrument
panel (Figure 7-8).
Oil pressure is also sensed by a pressure switch
that will turn on the LO OIL PRES light (see
“Annunciator Panel” section) if oil pressure is
below 5 psi. The oil pressure gages must be
checked to determine the problem engine.
NOTE
Learjet Model 23 airplanes do not
have low oil pressure warning lights.
Oil temperature is sensed by a resistance bulb
in the oil tank and transmitted to separate left
and right OIL TEMP gages located on the in-
strument panel. The oil pressure gages require
26 VAC. The OIL TEMP gages and the LO OIL
PRES lights require 28 VDC.
Operation
Figure 7-9 illustrates operation of the engine
oil system.
7-9
FOR TRAINING PURPOSES ONLY
LEARJET 20 SERIES PILOT TRAINING MANUAL
FlightSafety
international
FOR TRAINING PURPOSES ONLY
FOR TRAINING PURPOSES ONLY
OIL
PRESS
L R
PRESS
RATIO
3.0
2.5
1.5
1.0
2.0
PRESS
RATIO
3.0
2.5
1.5
1.0
2.0
EXH.
TEMP
°
C x 100
10
9
8
7
6
5
4
3
2
1
0
10
20
PERCENT
RPM
30
40
50
60
70
80
90
100
0
1
2
3
4
5
6
7
8
9
10
20
PERCENT
RPM
30
40
50
60
80
90
100
0
1
2
3
4
5
6
7
8
9
2
3
1
100
150
P.S.I.
200
50
FUEL FLOW
Lbs/Hr x 1000
0
L
EXH.
TEMP
°
C x 100
10
9
8
7
6
5
4
3
2
1
0
R
Figure 7-8. Center Instrument Panel
