1996 LAND ROVER DEFENDER Workshop Manual

COOLING SYSTEM
1
DESCRIPTION AND OPERATION ENGINE COOLING SYSTEM
Description
The complete cooling system of the 300Tdi engine
incorporates three independent functions:- Engine
(coolant) cooling; Turbo (charge air) intercooling;
Engine oil cooling.The intercooler is a separate aluminium unit, located
on the LH side of the engine compartment adjacent to
the radiator, sharing the same upper and lower
mountings. For details of turbo intercooling
See
FUEL SYSTEM, Description and operation,
Operation
. The oil cooler matrix is an integral part of
the radiator. Pre-formed pipes/hoses are used to link
the components within the separate systems as
shown below.
Engine cooling system
1.Radiator
2.Thermostat housing
3.Radiator bottom hose
4.Viscous fan
5.Water pump
6.Radiator top hose
7.Heater return hose
8.Coolant supply hose
9.By-pass hose
10.Radiator bleed (purge) hose
11.Bleed (purge) hose, thermostat housing
12.'Y' piece ejector
13.Expansion tank14.Heater rail
15.Heater unit
16.Heater feed hose
17.Intercooler
18.Air cleaner
19.Air feed hose
20.Turbocharger
21.Charge air supply pipe/hose
22.Cooled charge air supply hose
23.Exhaust manifold
24.Engine oil cooler
25.Feed pipe, engine oil cooler
26.Return pipe, engine oil cooler
27.Oil filter

26COOLING SYSTEM
2
DESCRIPTION AND OPERATION ENGINE (COOLANT) COOLING
Description
The 300Tdi engine uses a pressurised cooling system
and cross flow radiator which is supplied with coolant
from an expansion tank mounted on the RH side of
the engine compartment. A belt driven centrifugal
water pump, fitted to an auxiliary mounting assembly,pumps coolant to the engine crankcase, cylinder head
and vehicle heater unit.
An eleven bladed fan, incorporating a viscous
coupling, is driven by an independent pulley secured
to the front cover plate. The thermostat housing,
bolted to the front of the cylinder head, is fitted with a
vent valve that purges excessive air pressure and
coolant back to the expansion tank.
Engine coolant circulation (engine warm - thermostat open).
1.Radiator
2.Thermostat/housing
3.Radiator bottom hose
4.Viscous fan
5.Water pump
6.Radiator top hose
7.Heater return hose
8.Coolant supply hose9.By-pass hose
10.Radiator bleed (purge) hose
11.Thermostat housing bleed (purge) hose
12.'Y' piece ejector
13.Expansion tank
14.Heater rail
15.Heater unit
16.Heater feed hose

COOLING SYSTEM
3
DESCRIPTION AND OPERATION COOLANT CIRCULATION
Operation
When the engine is started from cold the thermostat
(2) prevents coolant circulation through the radiator by
closing off the top hose (6). During the engine warm
up period the water pump (5) circulates coolant to the
cylinders in the crankcase and through separate ports
to the cylinder head. At the rear of the cylinder head a
proportion of the flow is diverted through a heater feed
pipe (16) to the matrix of the heater unit (15). The
coolant is then carried, via a heater return rail (14) and
hoses (7), back to the water pump. The remaining
coolant flows through a by-pass hose (9) at the
thermostat housing and back to the water pump to
complete the first cycle.
When the normal engine running temperature is
reached, the thermostat opens, closing off the by-pass
hose (9). Coolant is then circulated via the top hose
(6) and through the radiator, where it is cooled and
drawn from the radiator bottom hose (3) by the water
pump (5). The coolant circulation through the
crankcase and cylinder head remains the same.
Two bleed pipes (10) and (11) help control the system
pressure by purging excess air and coolant to the
expansion tank via the 'Y'piece ejector (12).VISCOUS FAN
Description
The viscous drive unit for the engine cooling fan,
provides a means of controlling the speed of the fan
relative to the running temperature of the engine. The
viscous unit is a type of fluid coupling, which drives
the fan blades by means of 'silicone fluid'.
1.Input (drive) member
2.Output (driven) member
3.Sensing mechanism (bi-metal coil)
The fan drive has to be engaged only periodically,
between 5% and 10%, during normal operating
conditions, because the engine is cooled by ram air
for most of the time.

26COOLING SYSTEM
4
DESCRIPTION AND OPERATION Operation
To engage and disengage the fan drive the bi-metal
coil senses air temperature behind the radiator. When
a pre-determined temperature is reached, the coil
opens a valve (5) which allows fluid to enter the drive
area and, due to centrifugal force, circulates to the
annular drive area.
There are two sets of annular grooves (3), one in the
drive clutch and the other in the drive body, a specific
clearance being provided between the two sets of
grooves.
Viscous unit disengaged (engine at normal
running temperature)
1.Input (drive) member
2.Output (driven) member
3.Running clearance
4.Pump plate
5.Valve (closed)
6.Sensing mechanism (bi-metal coil)
7.Fluid seal
8.Bearing, input member
9.Fluid chamber
10.Fluid reservoirWhen this clearance is filled with viscous fluid, a
shearing action, caused by the speed differential
between the two drive components, transmits torque
to the fan. The fluid is thrown to the outside of the unit
by centrifugal force from where it is recirculated to the
reservoir (10) via the pump plate (4) adjacent to the
drive member.
If the engine speed is increased the amount of slip will
also increase to limit the maximum fan speed.
When the air temperature from the radiator drops
sufficiently, the bi-metal coil closes the valve and
prevents fluid entering the drive area. The fluid that is
in the drive area will gradually pump out into the
reservoir (10) and the fan will return to an idle
condition.
Viscous unit engaged (hot running temperature)
Bi-metal coil (6) expanded, valve (5) open.

COOLING SYSTEM
1
ADJUSTMENT DRAIN AND REFILL COOLING SYSTEM
Service repair no - 26.10.01
Draining
WARNING: DO NOT remove caps or plugs
when the engine is hot. The cooling
system is pressurised and personal
scalding could result.
1.Remove expansion tank filler cap.
2.Position a clean container under radiator if
coolant is to be reused.
3.Disconnect radiator bottom hose and allow
coolant to drain.
NOTE: A chassis undertray may be fitted
on some vehicle derivatives to conform to
legal requirements. When under chassis
remove and refit procedures are required, it may
be necessary to remove the undertray and/or
integral access panels.
See CHASSIS AND BODY,
Repair, Front undertray
orSee CHASSIS AND
BODY, Repair, Rear undertray
4.When expansion tank has emptied remove
thermostat housing plug to assist drainage.
5.Similarly when coolant is below top of radiator,
remove radiator plug.
6.Fit radiator bottom hose and fully tighten hose
clip.Refill
CAUTION: It is important that the correct
procedure is followed when refilling or
topping up the cooling system to avoid
trapping air in the system.
7.Fill cooling system with 50% - 50% of
water/anti-freeze mixture
See LUBRICANTS,
FLUIDS AND CAPACITIES, Information,
Recommended lubricants and fluids
8.Fill through expansion tank until radiator is full,
with level in expansion tank the same as
radiator.
NOTE: Care should be taken to avoid
excess coolant spillage.
9.Fit plastic plug in radiator.
10.Add a further 1 litre (1.76 pints) of coolant into
expansion tank and allow to settle.
11.Refit expansion tank cap and thermostat
housing plug.
12.Run engine at idle speed for 5 minutes.
13.Switch off engine and allow to cool.
14.Check that coolant in expansion tank is level
with top of indicator post. Top up if necessary.

COOLING SYSTEM
1
REPAIR VISCOUS COUPLING AND FAN
Service repair no - 26.25.19 - Viscous coupling
Service repair no - 26.25.05 - Fan
Remove
NOTE: The viscous coupling has a LH
thread.
1.Disconnect battery.
2.Using special pulley restraining toolLRT-12-094
and special spannerLRT-12-093unscrew
viscous coupling from pulley hub adaptor thread.
3.Remove viscous coupling and fan from vehicle.
NOTE: If air conditioning is fitted, the fan
cowl will also need removing,
See Fan
cowl
, with the viscous fan unit.
4.If required, remove 4 screws and release
viscous unit from fan blade.
Refit
5.Fit viscous unit to fan blades.
6.If applicable, fit fan cowl.
See Fan cowl
7.Carefully position viscous coupling and fit onto
pulley hub adaptor thread.
8.Using special pulley retaining tool, spanner and
a suitable torque wrench, tighten assembly to
45
Nm (33 lbf/ft).

26COOLING SYSTEM
2
REPAIR FAN COWL
Service repair no - 26.25.11
Remove
1.Disconnect battery.
2.Drain coolant.
See Adjustment, Drain and
refill cooling system.
3.Slacken retaining clips and remove radiator top
hose.
4.Slacken retaining clip and remove top hose from
intercooler.
NOTE: On vehicles fitted with EGR system,
remove complete intercooler top hose
assembly.
5.Remove viscous coupling and fan
See Viscous coupling and fan.
6.Remove 2 nuts securing top of fan cowl.
7.Release expansion tank hose from clips at base
of fan cowl.
8.Lift and remove cowl .
NOTE: On vehicles fitted with air
conditioning, it will be necessary to
remove the cowl and viscous fan unit
together to enable clearance of the compressor.Refit
9.Position fan cowl.
10.Fit viscous fan unit.
See Viscous coupling
and fan
11.Fit expansion tank hose into fan cowl clips.
12.Secure top of fan cowl to radiator top cover.
13.Fit intercooler top hose.
14.Fit radiator top hose.
15.Refill cooling system.
See Adjustment, Drain
and refill cooling system
16.Reconnect battery.
FAN PULLEY
Service repair no - 26.25.04.
Remove
1.Disconnect battery.
2.Remove viscous fan unit.
See Viscous
coupling and fan
3.Remove drive belt.See ELECTRICAL, Repair,
Auxiliary drive belt
4.Unscrew 4 bolts and remove pulley from adaptor
boss.
Refit
5.Fit fan pulley to adaptor boss. Tighten bolts to
25
Nm (18 lbf/ft).
6.Fit drive belt.See ELECTRICAL, Repair,
Auxiliary drive belt
7.Fit viscous fan unit.See Viscous coupling
and fan
8.Reconnect battery.

COOLING SYSTEM
3
REPAIR WATER PUMP
Service repair no - 26.50.01
Remove
1.Disconnect battery.
2.Drain cooling system.
See Adjustment, Drain
and refill cooling system
3.Remove radiator top hose.
4.Remove intercooler top hose.
5.Slacken water pump and power steering pump
pulley retaining bolts.
6.Remove drive belt.
See ELECTRICAL, Repair,
Auxiliary drive belt
7.Unscrew flange nut and remove belt tensioner.
8.Remove oil filler cap and remove rocker cover
insulation.
9.Slacken retaining clip and disconnect hose at
heater rail.
10.Unscrew 3 bolts and remove water pump pulley.
11.Unscrew 3 bolts and remove power steering
pump pulley.
12.Remove 8 bolts securing water pump, noting
location of 3 through bolts into cylinder block.
13.Withdraw pump and gasket from auxiliary
mounting bracket.
14.Clean all gasket material from mating faces.
Refit
15.Using new gasket, fit water pump to mounting
bracket. Tighten bolts to
25 Nm (18 lbf/ft).
16.Fit power steering pump pulley.
17.Fit water pump pulley. Tighten bolts of both
pulleys to
25 Nm (18 lbf/ft).
18.Fit drive belt.See ELECTRICAL, Repair,
Auxiliary drive belt
19.Fit hose at heater rail.
20.Fit rocker cover insulation and oil filler cap.
21.Fit drive belt tensioner. Tighten retaining nut to
45 Nm (33 lbf/ft).
22.Fit intercooler top hose.
23.Fit radiator top hose.
24.Refill cooling system.
See Adjustment, Drain
and refill cooling system
25.Reconnect battery.