1999 LAND ROVER DEFENDER heater

26COOLING SYSTEM
6
DESCRIPTION AND OPERATION By-pass flow valve
The by-pass flow valve is held closed by a light spring. It operates to further aid heater warm-up. When the main
valve is closed and the engine speed is below 1500 rev/min, the coolant pump does not produce sufficient flow
and pressure to open the valve. In this condition the valve prevents coolant circulating through the by-pass circuit
and forces the coolant through the heater matrix only. This provides a higher flow of warm coolant through the
heater matrix to improve passenger comfort in cold conditions.
When the engine speed increases above 1500 rev/min the coolant pump produces a greater flow and pressure
than the heater circuit can take. The pressure acts on the flow valve and overcomes the valve spring pressure,
opening the valve and limiting the pressure in the heater circuit. The valve modulates to provide maximum coolant
flow through the heater matrix and yet allowing excess coolant to flow into the by-pass circuit to provide the
engines cooling needs at higher engine rev/min.
Outlet Housing
A cast aluminium outlet housing is attached to the cylinder head with three bolts and sealed with a gasket. Coolant
leaves the engine through the outlet housing and is directed through a hose to the heater matrix, the radiator or
the by-pass circuit.
An Engine Coolant Temperature (ECT) sensor is installed in a threaded port on the side of the outlet housing. The
sensor monitors coolant temperature emerging from the engine and sends signals to the Engine Control Module
(ECM) for engine management and temperature gauge operation.
Expansion Tank
The expansion tank is located in the engine compartment. The tank is made from moulded plastic and attached to
brackets on the right hand inner wing. A maximum coolant when cold level is moulded onto the tank.
Excess coolant created by heat expansion is returned to the expansion tank from the radiator bleed pipe at the top
of the radiator. An outlet pipe is connected into the coolant pump feed hose and replaces the coolant displaced by
heat expansion into the system when the engine is cool.
The expansion tank is fitted with a sealed pressure cap. The cap contains a pressure relief valve which opens to
allow excessive pressure and coolant to vent through the overflow pipe. The relief valve is open at a pressure of
1.4 bar (20 lbf.in) and above.
Heater Matrix
The heater matrix is fitted in the heater assembly inside the passenger compartment. Two pipes pass through the
bulkhead into the engine compartment and provide coolant flow to and from the matrix. The pipes from the
bulkhead are connected to the matrix, sealed with’O’rings and clamped with circular rings.
The matrix is constructed from aluminium with two end tanks interconnected with tubes. Aluminium fins are
located between the tubes and conduct heat from the hot coolant flowing through the tubes. Air from the heater
assembly is warmed as it passes through the matrix fins. The warm air is then distributed in to the passenger
compartment as required.
When the engine is running, coolant from the engine is constantly circulated through the heater matrix.
ProCarManuals.com

COOLING SYSTEM
7
DESCRIPTION AND OPERATION Radiator
The 44 row radiator is located at the front of the vehicle in the engine compartment. The cross flow type radiator is
manufactured from aluminium with moulded plastic end tanks interconnected with tubes. The bottom four rows are
separate from the upper radiator and form the lower radiator for the fuel cooler. Aluminium fins are located
between the tubes and conduct heat from the hot coolant flowing through the tubes, reducing the coolant
temperature as it flows through the radiator. Air intake from the front of the vehicle when moving carries the heat
away from the fins. When the vehicle is stationary, the viscous fan draws air through the radiator fins to prevent
the engine from overheating.
Two connections at the top of the radiator provide for the attachment of the top hose from the outlet housing and
bleed pipe to the expansion tank. Three connections at the bottom of the radiator allow for the attachment of the
bottom hose to the thermostat housing and the return hose from the oil cooler and the feed hose to the fuel cooler.
The bottom four rows of the lower radiator are dedicated to the fuel cooler. The upper of the two connections at
the bottom of the radiator receives coolant from the oil cooler. This is fed through the four rows of the lower
radiator in a dual pass and emerges at the lower connection. The dual pass lowers the coolant temperature by up
to 24°C before being passed to the fuel cooler. Two smaller radiators are located in front of the cooling radiator.
The upper radiator is the intercooler for the air intake system and the lower radiator provides cooling of the
gearbox oil.
Pipes and Hoses
The coolant circuit comprises flexible hoses and metal formed pipes which direct the coolant into and out of the
engine, radiator and heater matrix. Plastic pipes are used for the bleed and overflow pipes to the expansion tank.
A bleed screw is installed in the radiator top hose and is used to bleed air during system filling. A drain plug to
drain the heater and cylinder block circuit of coolant is located on the underside of the coolant pump feed pipe.
Oil Cooler
The oil cooler is located on the left hand side of the engine block behind the oil centrifuge and oil filter. Oil from the
oil pump is passed through a heat exchanger which is surrounded by coolant in a housing on the side of the
engine.
Full water pump flow is directed along the cooler housing which also distributes the flow evenly along the block
into three core holes for cylinder cooling. This cools the engine oil before it is passed into the engine. A small
percentage of the coolant from the oil cooler passes into a metal pipe behind the engine. It then flows into the
lower radiator via a hose.
Fuel Cooler
The fuel cooler is located on the right hand side of the engine and is attached to the inlet manifold. The cooler is
cylindrical in design and has a coolant feed connection at its forward end. A’T’connection at the rear of the cooler
provides a connection for the coolant return from the heater matrix and coolant return from the fuel cooler.
The’T’connection houses a thermostat which opens at approximately 82°C. This prevents the cooler operating in
cold climates. Two quick release couplings on the cooler allow for the connection of the fuel feed from the
pressure regulator and return to the fuel tank. A counter flow system is used within the cooler.
Fuel flows around a coolant jacket within the cooler and flows from the back to the front of the cooler. As the hot
fuel cools travelling slowly forwards it meets progressively colder coolant travelling in the opposite direction
maintaining a differential cooling effect.
ProCarManuals.com

COOLING SYSTEM
11
DESCRIPTION AND OPERATION OPERATION
Coolant Flow - Engine Warm Up
During warm up the coolant pump moves fluid through the cylinder block and it emerges from the outlet housing.
From the outlet housing, the warm coolant flow is prevented from flowing through the upper and lower radiators
because both thermostats are closed. The coolant is directed into the heater circuit.
Some coolant from the by-pass pipe can pass through small sensing holes in the flow valve. The warm coolant
enters a tube in the thermostat housing and surrounds 90% of the thermostat sensitive area. Cold coolant
returning from the radiator bottom hose conducts through 10% of the thermostat sensitive area. In cold ambient
temperatures the engine temperature can be raised by up to 10°C (50°F) to compensate for the heat loss of the
10% exposure to the cold coolant return from the radiator bottom hose.
At engine speeds below 1500 rev/min, the by-pass valve is closed only allowing the small flow through the sensing
holes. As the engine speed increases above 1500 rev/min, the greater flow and pressure from pump overcomes
the light spring and opens the by-pass flow valve. The flow valve opens to meet the engine’s cooling needs at
higher engine speeds and prevents excess pressure in the cooling system. With both thermostats closed,
maximum flow is directed through the heater circuit.
The heater matrix acts as a heat exchanger reducing the coolant temperature as it passes through the matrix.
Coolant emerges from the heater matrix and flows to the fuel cooler’T’connection via the heater return hose.
From the fuel cooler the coolant is directed into the coolant pump feed pipe and recirculated around the heater
circuit. In this condition the cooling system is operating at maximum heater performance.
Coolant Flow - Engine Hot
As the coolant temperature increases the main thermostat opens. This allows some coolant from the outlet
housing to flow through the top hose and into the radiator to be cooled. The hot coolant flows from the left tank in
the radiator, along the tubes to the right tank. The air flowing through the fins between the tubes cools the coolant
as it passes through the radiator.
A controlled flow of the lower temperature coolant is drawn by the pump and blended with hot coolant from the
by-pass and the heater return pipes in the pump feed pipe. The pump then passes this coolant, via the cylinder
block, to the oil cooler housing, cooling the engine oil before entering the block to cool the cylinders.
When the fuel temperature increases, the heat from the fuel conducts through the fuel cooler’T’connection and
causes the fuel thermostat to open. Coolant from the cylinder block flows through the oil cooler and via a pipe and
hose enters the lower radiator. The lower temperature coolant from the oil cooler housing is subjected to an
additional two passes through the lower radiator to further reduce the coolant temperature. From the lower radiator
the coolant flows , via a hose, to the fuel cooler.
As the hot fuel cools, travelling slowly forwards through the cooler, it meets the progressively colder coolant
travelling in the opposite direction from the lower radiator.
ProCarManuals.com

COOLING SYSTEM
1
ADJUSTMENT DRAIN AND REFILL
Service repair no - 26.10.01
WARNING: Hot coolant
Drain
1.Remove engine acoustic cover.
2.Visually check engine and cooling system for
signs of coolant leaks.
3.Examine hoses for signs of cracking, distortion
and security of connections.
4.Position drain tray to collect coolant.
5.Remove expansion tank filler cap.
6.Loosen clip screws securing air inlet hose to
intercooler and inlet manifold, release and
remove hose.
7.Release clip and disconnect bottom hose from
radiator.
8.Allow cooling system to drain.
9.Disconnect bottom hose from radiator.Refill
1.Flush system with water under low pressure.
2.Do not use water under high pressure as it could
damage the radiator.
3.Connect bottom hose to radiator and secure
hose with clip.
4.Prepare coolant to required concentration.
5.Position heater temperature control to maximum
hot position.
6.Remove bleed screw from top hose.
7.Fill system slowly through coolant expansion
tank until a steady flow of coolant is emitted from
the bleed hole in top hose.
8.Fit bleed screw to top hose.
9.Continue filling system until coolant level
reaches’MAX’mark on expansion tank.
10.Fit expansion tank filler cap.
11.Position air intake hose and tighten clip screws.
12.Start and run engine until normal running
temperature is reached.
13.If fitted, DO NOT operate air conditioning.
14.Switch off engine and allow to cool.
15.Check for leaks and top-up coolant to’MAX’
mark on expansion tank.
ProCarManuals.com

37MANUAL GEARBOX
8
REPAIR
12.Remove 13 screws securing tunnel cover.
13.Release and remove tunnel cover.
14.Remove cooling fan.See COOLING SYSTEM,
Repair.
15.Remove air filter.See FUEL SYSTEM, Repair.
16.Remove 2 upper bolts securing clutch housing to
engine.
17.Remove bolt securing shim to clutch housing.
18.Release gearbox breather pipes from clips on
heater hose.
19.Remove starter motor.See ELECTRICAL,
Repair.
20.Remove exhaust front pipe.See MANIFOLD
AND EXHAUST SYSTEM, Repair.
21.Drain gearbox oil.See Adjustment.
22.Drain transfer gearbox oil.See
MAINTENANCE ,
23.Remove 3 nuts securing intermediate silencer to
tail pipe.
24.Release silencer from mounting rubbers, remove
silencer and discard gasket.
25.Mark front and rear propeller shaft to transfer
gearbox flanges for reassembly purposes.
ProCarManuals.com

MANUAL GEARBOX
11
REPAIR Refit
44.Clean gearbox to engine mating faces, dowels
and dowel holes.
45.With assistance raise gearbox on jack and align
to clutch and engine.
46.Fit lower bolts securing clutch housing to engine
and tighten to50 Nm (37 lbf.ft).
NOTE: Do not fit upper bolts at this stage.
47.Fit earth leads and secure with bolt.
48.Connect Lucars to differential lock switch,
multiplug to reverse light switch, position
multiplug to bracket and connect low ratio detect
multiplug - if fitted.
49.Raise gearbox jack and guide transfer gearbox
lever through tunnel.
50.Secure body harness clips to bracket on top of
transfer gearbox.
51.Position battery earth lead to transfer gearbox
and tighten retaining nut.
52.Connect multiplug to speed sensor and secure
harness in clip on transfer gearbox.
53.Position mounting brackets and rubber
mountings, positioning heat shield to LH
mounting and tighten bracket bolts to85 Nm (63
lbf.ft).
54.Position nuts to mountings and tighten to48 Nm
(35 lbf.ft).
55.Remove 3 bolts securing support plate
LRT-99-007to gearbox.
56.Position handbrake cable through heel board.
57.Position clutch slave cylinder, fit bolts and
tighten to25 Nm (18 lbf.ft).
58.Clean propeller shafts and mating faces.
59.Position propeller shafts, align to marks and
tighten nuts to48 Nm (35 lbf.ft).
60.Clean intermediate silencer and tail pipe mating
faces.
61.Position silencer and secure on mountings,
using a new gasket align to tail pipe, fit nuts and
tighten to25 Nm (18 lbf.ft).
62.Refill gearbox with oil.See Adjustment.
63.Refill transfer gearbox with oil.See
MAINTENANCE ,
64.Fit exhaust front pipe.See MANIFOLD AND
EXHAUST SYSTEM, Repair.
65.Refit starter motor.See ELECTRICAL, Repair.
66.Fit bolt securing shim plate to clutch housing and
tighten10 Nm (7 lbf.ft).
67.Position heater pipe to gearbox housing, fit
upper bolts securing clutch housing to engine
and tighten to50 Nm (37 lbf.ft).
68.Position gearbox breather pipes to clips on
heater hose.69.Fit air cleaner.See FUEL SYSTEM, Repair.
70.Fit cooling fan.See COOLING SYSTEM,
Repair.
71.Fit and align tunnel cover, fit and tighten screws.
72.Position relay panel, fit spacers and tighten
screws.
73.Position hand-brake lever and tighten bolts to25
Nm (18 lbf.ft).
74.Connect handbrake cable to lever, fit clevis pin,
washer and new split pin.
75.Connect Lucar to hand-brake switch.
76.Position gaiter to handbrake lever and secure
with trim stud.
77.Locate insulation pad over gear levers and fit to
tunnel cover.
78.Align spline marks, fit gear lever to lower lever,
fit washer and secure with retaining nut.
79.Position gear lever cover.
80.Position gearbox tunnel carpet.
81.Fit gear lever and transfer gear lever knobs.
82.Reconnect battery negative lead.
83.Fit battery cover.
ProCarManuals.com

76CHASSIS AND BODY
4
REPAIR WING - FRONT
Service repair no - 76.10.24
Remove
1.Remove wheel arch liner.See this Section.
2.Remove front grille.See this Section.
3.Release fixings and remove cooling fan cowl.
4.Remove air cleaner grille from front wing.
5.Remove 4 screws securing air intake elbow to
wing.
6.Remove 7 screws and remove heater air intake
grille from wing.
7.Remove 2 bolts securing heater air intake
bracket to inner wing. Remove bracket.
8.Remove heater air intake from wing and collect
seal.
9.Remove 2 bolts securing EGR solenoid to inner
wing and lay aside.
10.Remove 3 studs securing expansion tank pipe to
inner wing.
11.Remove 2 bolts securing PAS reservoir to inner
wing and lay aside.
12.Remove 4 bolts securing outer wing to inner
wing.
ProCarManuals.com

CHASSIS AND BODY
7
REPAIR Refit
29.Fit bonnet cable grommet.
30.Fit side repeater lamp to wing.
31.Fit headlamp sealing ring, fit headlamp and
tighten screws.
32.Fit headlamp finisher, side and indicator lamps
and tighten screws.
33.Fit grille support bracket and tighten bolt.
34.With assistance, position and align wing to body
and locate bonnet cable to wing.
35.Connect headlamp, indicator, side lamp and side
repeater lamp multiplugs.
36.Fit bolt securing wing to bulkhead.
37.Fit bolts securing wing to’A’post.
38.Fit nut and bolt securing support stay to wing.
39.Fit bolt securing inner and outer wing to chassis.
40.Fit bolts securing radiator bracket to wing.
41.Fit bolts securing outer wing to inner wing.
42.Align wing and finally tighten all bolts.
43.Position wheel arch extension to wing, and fit
securing studs.
44.Position PAS reservoir to wing and tighten bolts.
45.Position expansion tank pipe and secure with
studs.
46.Position EGR solenoid and tighten bolts.
47.Position heater air intake seal and fit air intake.
48.Fit heater air intake bracket and tighten bolts.
49.Fit heater air intake grille and tighten screws.
50.Align air cleaner intake elbow, tighten screws
and fit grille.
51.Fit wheel arch liner.See this Section.
52.Position bonnet release cable to lock and tighten
screw.
53.Fit cooling fan cowl.
54.Fit front grille.See this Section.STEP - FOLDING - REAR DOOR
Service repair no - 76.10.41
Remove
1.Remove 2 bolts securing step to chassis
member, remove step and collect spacers.
Refit
2.Position step, fit spacer washers and tighten
bolts.
ProCarManuals.com