Overheating
V12 E Type
[May
2002 Jaguar Enthusiasts]
Overheating
V12 E-Types are not unusual and there are several steps to follow
before getting too involved.
Cooling Fans
Firstly, are the cooling fans drawing air through the radiator
towards the engine? If the air is being drawn from the engine
bay out then this is wrong and someone has wired the fans incorrectly.
Cooling System
The thermostats should be of the 74 degree C-type [although these
are getting more difficult to find these day - SNG Barratt] and
must have an air bleed hole, called a jiggle pin. This pin must
be fitted at the 12 O'clock position, if not buy the correct thermostats.
The air bleed hoses from the plenum chambers to the expansion
tank must be clear. This also means the pipes leading out from
the plenums must be blown through and likewise the entries into
the expansion tank. Drill out the solid sediment deposits if necessary.
The expansion tank must have a 16 psi cap on it, preferably a
Jaguar one, they are only £5.00 + VAT.
Ensure the radiator matrix exterior is clean and clear of leaves,
pollen, or even mice, etc. Use a jet wash to clean it through.
The distributor vacuum capsule should be functioning and corrected
to a permanent vacuum source located under the rear L/h carburetor.
Stroboscopic Timing
The principle of using a stroboscopic light to determine the ignition
timing is that a flashing light [activated every time the spark
is produced on the high tension lead to which it is connected]
is directed onto a rotating component [such as a crankshaft pulley]
which appears to the eye to be stationary so that the relationship
between the TDC mark and the timing plate can be seen. On the
Jaguar V12 engine the TDC mark is usually on the pulley and the
degree plate attached to the engine as shown below.
When checking stroboscopic ignition timing it is essential that
the engine runs below the speed at which the centrifugal ignition
advance mechanism in the distributor begins to operate. An engine
speed of 750 rpm or less is usually suitable for this purpose
although other criteria may be specified in the relevant date.
If the engine is allowed to run at a speed where the centrifugal
advance mechanism is in operation the stroboscopic timing will
be the static figure plus the amount by which the distributor
has advanced.
An
example of this is as follows:
Static
Timing: 12 degrees BTDC
Centrifugal
advance: 8 degrees BTDC
Total
advance: 20 degrees BTDC
The
difficulty in the initial stages of setting the timing is that a
large error [either advance or retard] can have considerable effect
on the engine's idle speed. Ignition timing that is too far retarded
will, provided that it is within reasonable limits, usually cause
an increase in engine idle speed and vice versa if the timing is
retarded. What this means in practice is that adjusting the ignition
timing may alter the engine idle speed which in turn can effect
the operation of the distributor centrifugal advance mechanism and
hence the ignition timing. Stroboscopic timing for a UK specification
Jaguar V12 E-Type is as follows:
When
using 97 octane petrol
12
degrees before top dead centre [BTDC] at an idle speed of no more
than 750 rpm with the vacuum capsule disconnected.
When
using 95 octane petrol
8
degrees before top dead centre [BTDC] at an idle speed of no more
than 750 rpm with the vacuum capsule disconnected
The
distributor mechanical advance should function smoothly and the
air gap between the rotor and pick up should be around 0.018".
If all the above checks out then it is time to look deeper.
Radiator
If the radiator has not been re-cored for several years then have
it done and have a modern high efficiency core put in. There is
no point being a slave to originality if the car cannot be driven
and not one can see the radiator anyway. Although a flow check may
indicate the radiator is OK, the chemical deposits on the inside
of the tubes will greatly reduce the rate of heat transfer.
Water Pump
Remove the water pump to see if excess corrosion has affected the
timing chain case, so reducing its' efficiency.
Engine
If it is still causing a problem then the engine itself may require
a partial strip down. Sediment can build up in a poorly maintained
engine and set hard. This can build up to around the cylinder liners
and reduce the flow of coolant quite dramatically. The only solution
is removal of the cylinder heads but this is not a decision to be
taken lightly.
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