1998 JAGUAR X308 Coolant

Engine Cooling
- Engine Cooling
Descr
i
ption and Operation
Engine Cooling Comp onents - Normally Aspirated Vehicles

Engine cooling is via a low volume, high velocity system which achieves a very fast warm up. The temperature of the
combustion chambers is reduced along with a more even temperature distribution. The temperature of the bores is increased.

F r
om the pump, coolant flows into each bank of the cylinder bl
ock. In each bank, approximately 50% of the coolant cools the
cylinder bores and the remainder is diverted th rough the bypass gallery to the cylinder head.
With the thermostat closed, coolant returns directly to the pump through the bypass on the thermostat housing.
With the thermostat open, coolant returns to the pump via the radiator.
The cooling system uses a mixture of water and Jaguar Anti-Freeze/Inhibitor (Dow 542).
The cooling system on a supercharged engine is similar, but has additional components for cooling the intake air.
Engine Cooling Co mponents - Supercharged Vehicles
ItemDescrip
tion
1Thr
ottle B
ody
2Hea
ter Return
3Coolant Pum p
4Ther
mostat Housing
5Vehicle Radia
t
or
6Hea
ter Su
pply
7Bleed
Outl
et (to expansion tank)
8EGR V
a
lve (when fitted)
9Bleed
Outl
et (to expansion tank)

T
he cooling system for the supercharged engine is very similar
to the normally aspirated engine, but with the addition of a
water cooled, intake air charge cooling system. This comprises a radiator, an electrically operated water pump and two
charge air cooler assemblies (heat exchangers) - one for each bank. The system works independently, but is connected to the
main cooling system at the bottom hose to allow for therma l expansion and to help to prevent unwanted circulation.
The condenser for the air conditioning system fits between th e coolant main radiator and the charge air cooling system
radiator.
Cylinder Block Heater, Drain Location
ItemDe
scription
1Rad

iator - Intake Air Coolant
2Ele

ctrically Operated Coolant Pump
3Top Hose
4Charge Air Coo

lers -
Intake Air Cooling
5Fi
lling Point for Intake Air Cooling
6N

on-Return Valves - Heater
7Ele

ctrically Operated Coolant Pump
8Hea

ter Matrix
9Wate

r Valve - Heater Control
10EGR V

alve (when fitted)
11Thr

ottle Body
12Coolan

t Recovery Bottle
13H

eader/Expansion Tank
14Eng

ine Coolant Pump
15The

rmostat Housing
16Bottom

Hose
17Air Bleed

Pipes
18Rad

iator - Main Cooling System

A coola n
t drain plug is located at the rear of the cylinder block.
Coolant may be drained from the A-bank, by removing the coolant pipe from behind the starter motor.
For vehicles fitted with the cold climate package, a cylinder block heater (shown) replaces the drain plug located on the B-
bank.
Coolant Pump and Flow Control

The coolant pump is fitted between the two cylinder banks, on the front face of the cylinder block.
The pump consists of a housing containing a shaft, with a sh rouded plastic impeller on one end and a drive pulley on the
other.
A pair of roller bearings support the shaft in the housing. A seal behind the impeller prevents coolant from contaminating the
bearings. Should this seal fail, coolant escapes from a witness hole in the housin g indicating that immediate action is
required.
An O-ring and an aluminum-alloy gasket, seal the ports between the pump and the cylinder banks.
Coolant Outlet Duct

A coola
nt outlet plastic pipe connects to the outlet port of ea
ch cylinder head to provide a common connection point for the
radiator top hose. It also incorporates the Engine Coolant Te mperature (ECT) sensor which provides a signal representing
coolant temperature at the cylinder heads. The outlet pipe has connections to supply the heater matrix and the bypass flow
to the thermostat housing. An in-groove ga sket, seals each of the outlet-to-cylinder head joints. An aluminium gasket seals
the ECT sensor to duct joint.
Coolant Outlet Duct - Supercharged

The coolant outlet duct on the supercharged engine performs exactly the same function as on the normally aspirated engine
and connects to the same ports on the engine. The main physical difference is that the thermostat housing has been
ItemDe
scription
1Bottom

Hose Connection
2The

rmostat Cover
3The

rmostat
4Coolan

t Outlet Duct
5B

reather Connection
6ECT Se

nsor
7Top Hose Conn

ection
8Bypa

ss to Water Pump
9Hea

ter Hose Connection

combin
ed with the outlet duct and consequently, there is no separate housin
g assembly fitted above the water pump, as used
on the normally aspirated engine. The illustration shows the outlet duct viewed from the engine.
Thermostat Housing

The plastic housing for the thermostat is fitted between th e two cylinder banks immediately above the coolant pump.
Controlling the coolant flow through the radiator, the thermostat starts to open at 80 ° to 84 °C and is fully open at 96 °C.
A duct in the cylinder block connects the thermostat housing outlet to the coolant pump inlet. The joint between the
thermostat housing and the cylinder block is via an in-groove seal.
An air bleed outlet vents an y air in the system into the expansion reservoir, durin
g normal operation. A removable cap (usin g
a hex key) allows air to vent from the system when filling from empty.
On supercharged engines, the thermostat housin g is combined with the coolant outlet duct.
Radiator

The cooling
pack incorporates the radiator a
ssembly with integral transmission oil cool er (located in the radiator outlet tank),
an air conditioning condenser, and the cooling fans and cowl assembly.
The cooling pack on supercharged vehicles is the same as described above, but with the addition of a charge air cooler
coolant radiator located in front of the condenser.
Radiator Mounti
ng/Retention
T
he radiator is mounted on four rubber mounts, one on each
end of the upper and lower horizontal face. The two lower
mountings are supported on two isolated brackets mounted on the body; the lower cradle assembly has subsequently been
deleted.
A closing panel made from polypropylene, which retains the radiat or assembly, fits over the top of the radiator and is bolted
to the vehicle top panel.
Coolant Hoses - Engine

Whe r
e considered necessary, some hose conn
ections have an indication mark to ensure correct orientation of the hose when
being fitted.
All joints use spring-band clips, except small pipes on the bleed system joints - which use cobra clips. The heater feed and
return hoses use quick-connection unions.
Supply and return hoses for the heater are located between the cylinder banks.
A connection on the rear of the A-bank provides coolant supply for the electronic throttle and the EGR valve (where fitted).
The outlet from the electronic throttle connects to the return hose from the heater.
Cool
ant Header and Recovery Tanks
A recovery system comp
rising the header tank
and a recovery tank is fitted. The recove ry tank is located in front of the left
hand front wheel arch liner.
The header tank provides the cooling system filling point and carries the coolant level sensor. The pressure cap allows
controlled release of coolant to the re covery tank during normal operation.
The recovery tank accommodates the expansion of the system coolant during normal operation. On engine cool-down, the
coolant contracts and is returned to the main system.
Coo lin
g Fans
The two
rad
iator cooling fans are mounted in
a cowl assembly within the cooling module.
The fans are controlled by the ECM dependent on the demand fr om the cooling system (temperature) or the air conditioning
ItemDescrip
tion
1EGR
E
ngines
2Non
-
EGR Engines
3Hea
ter Connections

s
ystem (pressure).
Outputs from the ECM control the radiator fans control module, located behind the left hand side of the bumper, to operate
the fans in the series mode (slow), paralle l mode (Fast) or Off modes. Hysteresis in the temperature and pressure switching
values prevents 'hun ting' between modes.
Under hot operating conditions, the fans may continue to operat e for some time after the engine has been switched off, but
will stop automatically when the coolant te mperature has been sufficiently reduced.
Engine Coolant Temperature Sensor (ECT) and ECM

The engine coolant temperature (ECT) sensor is located in the coolant outlet pipe and reacts to engine coolant temperature
changes, providing an input to the Engine Control Module (ECM). The sensor has a negative te mperature coefficient so that
the sensor resistance decrea ses as temperature rises.
Temperature / Resistance Relationship Graph

T
emperature / Resistance
Relationship Table