Rolls-Royce Bentley Corniche User Manual Page 14
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Section
L5
-%F
Thermostat
housing
assembly
The
thermostat housing is
situated
at
the forward end
of the induction manifold
(see
fig.
L5-'I
1.
It
is connected
to
the
induction manifold
by
transfer pipes.
All
cars
are
fitted
with the same thermostat
housing. However, various
themostat
outlet elbows
can
be
fitted,
dependent
upon the
specification
of the
vehicle.
A
number
of
electrical
switches
are
fitted
into the
thermostat housing dependent upon
the
specification
of the vehicle.
For
service
details
of
these
switches
refer
to
Electrical Manuals,
TSD
4701
(prior
to
1989
model year) or
TSD
4848
(1
989
model
year).
Thermostat
The
engine cooling
system
incorporates a
wax
element thermostat (see
fig.
L5-2).
When
the engine is
started
from
cold
the
thermostat
is
in
the
closed
position.
This
reduces the
engine
warm-up time
by
recirculating
the
coolant leaving
the
engine backto the
-
coolant
pump,
thus by-passingthe radiator.
As
the
cootant
approaches
its
normal working temperature
the
thermostat opens
and
allowsthe engine coolant to
flow
through the radiator. When
the
thermostat is
in
the fully open position
it
closes the
by-pass
circuit.
On
top
of
the thermostat
is
the bridge
piece
and
into this
is
secured the fixed piston rod.
The valve
assembly
containing
the
wax
capsule
seat,
is
on
the
underside
of
the
top flange.
ft
is
biased
in this position
by
a
spring
and
retained
by
a
'U'
piece.
A
second outer
'U'
piece
(by-pass
valve) loaded by
a
light poundage spring,
is
fitted
to
the
bottom
of
the
thermostat to operate the
by-pass
circuit.
The
top
flange
incorporates
a
vent
hole
containing
a jiggle pin.
This
vent allows
air
to
escape
when
the
cooling system is being filled.
When
the
system
is
operating the jiggle pin
rises
to close the vent.
Also
situated around the
top
flange are fusible
plugs.
These
plugs melt at approximately
124°C
(256F)
and
provide
vent holes for the coolant,
in
the
event
of
the thermostat
not
opening,
to
control
the
coolant temperature.
The
thermostat operates when
the
coolant
temperature approaches between
85°C
and
89°C
(185°F
and
192°F).
At this point
the
wax
in
the
capsule
changes its
state
and expands rapidly. The expansion
compresses
the
rubber
sleeve
forcing
it
off
the end
of
the
tapered piston rod.
As
the sleeve is an integral part
of
the
main
valve assembly, this movement
is
transmitted to the
valve
moving
it
downwards
off
its
seat.
A
small quantity
of
warm
coolant
is
then
allowed
to pass between the
valve
and
its
seat
to
the
radiator
matrix, where it
is
cooled.
Further rises in
engine
coolant temperature cause
a
progressive opening
of
the main valve until a
temperature of
between
99°C
and
'102°C
(210°F)
and
Fig.
IS-l
Thermostat
llousing
assembly
215°F)
is
mined. At
these
temperatures the main
valve
is
fully open [maximum travel
14.27
mm
(0.562
in)].
When
the
main
valve
assembly
has
opened
10
mm
(0.375
in),
the
by-pass
valve
on
the base of
the
thermostat
assembly
will
have
moved under spring
pressure sufficiently
to
close the coolant
by-pass
circuit
and
all
coolant
is then directed
to
the
radiator
matrix.
A
decrease in
engine
temperature will
cause
the
wax
in
the
capsule
to
contract
and,
due
to spring
pressure, close the main valve and also
open
the
by-pass circuit.
The
thermostat
main
valve
assembly,.
being
sensitive
to
the temperature
of
the surrounding
coolant, controls the
flow
of
coolant
to
the radiator
matrix to suit the requirements
of
the engine.
At
the service
internals
quoted
in the Service
Schedule Manual,
TSD
4702,
a newthermostat
should
be
fitted.
Do
not
attempt
to
adjust
the
thermostat.
Thermostat
-
To
remove
1.
Carry
out
the
usual workshop
safety
precautions.
2.
Drain approximately
half
the radiator coolant into
a
clean container
(see
Section
L31.
3.
Disconnect
the
eiectricaI connection from
the
thermostat outlet elbow.
4.
Remove
the
setscrews securing the outlet
etbow
to
the thermostat housing. Coliect the washers.
5.
Free the joint
and
lift off the thermostat cover.
6.
Lift
the thermostat out
of
the
housing.
- Workshop 1
- '-> 2
- Chapter 3
- Freezing 7
- Unscrew 10
- Radiator 11
- Thermostat 14
- Coolant 16
- Section 19
- DubChek 20
- Introduction 21
- Description 21
- Parts affected 21
- Applicable to 21
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