MGBGTV8 cooling and overheating concerns
The exceptionally hot and long Summer in the UK in 2003
has made us only too aware of how hot an MGBGTV8 can become and the
particular concerns over cooling. In this note Roger Parker thinks
through some of the issues and provides some useful suggestions. (Aug
The engine coolant
operating temperature is a function of the:
o heat generated by the engine.
o surface area and rate at which the heat can be transferred through
the engine block.
of the coolant to take up the heat from the block.
o flow of
coolant through the cooling system.
area and rate of heat transfer from coolant to radiator.
o rate of
transfer of heat from radiator to air and the,
temperature and rate of airflow through the radiator.Each
function is critical to the overall efficiency of the cooling system
and with the V8 there are some marginal aspects which have been well
documented. Here are however some additional and more recent concerns.
Age of the cooling system is an issue for all MGV8's - even
the RV8 can be 10 years old and the newest eight, irrespective of
when registered. MGBGTV8s are between 27 and 30 years old with some
earlier Costellos even older. Age has a degrading effect on the inside
surfaces of the cooling system with corrosion forming and deposits
building. Inside the engine block especially there is a tendency for
sludge settlement which slowly reduces the internal cooling system
volume and in those areas can see a blockage to heat flow. Radiators
of course are most susceptible due to their specific design to offer
the largest surface area to transfer heat through the matrix to the
surrounding air and by definition have many small bore tubes that
can block. Flow through the radiator is obviously going to be affected
by any debris that is flowing through the system, but another affect
is furring up of the inside of the radiator through the type of water
used in the cooling system. This is not normally a major issue except
after long periods of use with hard water, but overall in today's
conditions it is something to consider, even if the flow rate through
a radiator is strong.
Current petrol. A very big recent change (and impediment) is
current petrol. Not just unleaded as most people would think of first,
but all petrol with the possible exception of the genuine leaded petrol
available from around 160 outlets around the UK - see www.leadedpetrol.co.uk
for details. As we move closer to direct injection petrol engines
there is a need to modify the fuel to maximise the benefits from the
use of this technology. Older readers will recall in the 1960s and
70s (and probably before that too) when cars that were 30 plus years
old suffered from running problems that was directly attributable
to the make up of the fuel at that time. Well the same situation now
applies with a great many MGs, specifically B series engined cars,
but the effects are not restricted to those engines and they extend
to the V8 as well.
Essentially over the last couple of years the frequency of reported
owner problems with hot running or overheating MGBs has sky rocketed.
Whilst some problems can be attributed to well known problems such
as drive belt slackness, thermostat failure and less efficient radiators,
so many still suffer after almost everything in the cooling system
has been renewed. The numbers in this category clearly indicates there
is a more fundamental issue and whilst I have no actual evidence I
am clear in my mind that it is fuel that is at the root of the change.
There are no doubt many with a far greater depth of knowledge and
understanding of fuel make up and characteristics during combustion,
but since unleaded doesn't have the dampening effect of TEL (lead)
to slow the rate of the burn, it burns faster and reaches a higher
peak temperature. Quite whether the calorific value has altered I
don't know but if it has then it is possible that the overall heat
energy created is also greater. The B series engine conditions tends
to point in the direction that it does produce more heat. More heat
places more strain on the cooling system in the same way that placing
a cover over a section of the radiator would, so there is a need to
ensure that the system is as good and as efficient as it can be. In
the case of the V8 where cooling was always marginal the normal range
of cures previously adopted successfully may now no longer be adequate.
Climate change? Another aspect to consider is what appears
to be an increase in the frequency of warm/hot days so if the ambient
air temp is higher then heat transfer from the radiator will reduce.
Traffic volumes. Yet another aspect is one of traffic volumes
and the increased frequency of travelling at lower speeds thus reducing
the ram air effect through the radiator. It is well known that journey
times are increasing through increased traffic congestion and whilst
it may not be applicable to all, it is certainly a factor.
So what can we do to overcome these factors?
There are a number of areas where modifications can further improve
cooling efficiency. The fit of a 4 core in place of original 3 core
radiator helps only when the coolant and air flows are able to see
an increased heat transfer. Most overheating problems arrive during
slow speed driving or when stuck in traffic. In these conditions engine
rpms are low and with mechanical water pumps, the rotational speed
is a direct function of the engine speed as it is connected by the
fan belt and its efficiency is also low. Alter the pulley diameter
to increase pump rpm and whilst the coolant flow at idle and low engine
speeds will increase, at higher
to Contents listing
you will then see cavitation and no flow due to the pump speed being
Electric coolant pumps have started to appear and have for some
time been seen just on specialist applications, but more recently
these have started to migrate to road cars. The theory of the system
is very sound as full digital control of an electrically driven
water pump enables coolant flow to be right for the specific operating
conditions and offers the ability to remain at that optimum. It
certainly provides the ideal of anything up to maximum flow at idle
speeds - a major failing with the standard mechanical pump. Altering
the cooling system to fit an electric pump to take over from the
original pump makes a significant visual impact in the engine bay.
The principles may be right, but these items have not been around
long enough in general road use to generate the 'comfort factor'
most owners would need before following this route.
A half way house and one that is far more likely to be taken up
is to add a smaller flow additional electric pump to support the
original mechanical pump. Here the deficiency of the mechanical
pump at idle and low engine rpms can be overcome with an additional
electric water pump. If you set aside the aesthetics in the engine
bay, it would seem to be worthy of some serious consideration. Electric
operation also provides a facility to allow the pump to be operated
when the engine is not running and so heat soak immediately following
switching off of a hot engine can be significantly reduced. I would
suggest that if this facility was to be configured that a similar
connection be made to the cooling fans so that circulated hot water
can be cooled, with a proviso of a time restriction so that batteries
are not going to be flattened.
Alternative coolants. Using alternative coolants or adding
products known as 'Water Wetters' does work. The have been used
for many years with competition engines, especially where regulations
do not allow mechanical changes. So 'Water Wetters' and special
coolants are worthy of consideration. Essentially these appear to
break down the water surface tension and thus provide a better contact
between the coolant and the inner surfaces of the cooling system.
This is especially advantageous in the engine block where often
localised overheating creates a small area of boiling coolant (just
like the element in your kettle) and this means a poorer coolant
to surface contact. Special coolants and Water Wetters help to reduce
is vital and the MGB with a V8 blocking up the engine bay doesn't
have a very good through flow rate. It has to be remembered that
to get a good heat transfer there has to be a good contact between
the air and radiator core and by definition there is a resistance
to air flowing through the radiator. Air will then try and find
an easier route to flow through and here there are a number of options
for it to do so around the outside of the radiator. Looking at the
radiator and trying to eliminate any escape route for air flow is
a sound move. Under the car there is also scope for a substantial
duct to ensure air entering through the front valance is directed
to the exposed lower part of the radiator, although without fan
assistance this is only of benefit when the car is moving forward.
Cooling fans. The fans fitted as the original equipment on
an MGBGTV8 are dreadful. They move enough air, noisily, but this
air goes all over the place and not enough goes through the radiator
core. The issue of the distance between the fan blades and the radiator
core is critical to improving the flow through the radiator, but
there is much more that can be done. Look at any current fan system
and apart from the blade efficiency being higher leading to greater
flow and quieter running, the common factor for all is a deliberate
very close mounting to the radiator and a COWLING to ensure that
what air is moved passes through the radiator core. Put the palm
of your hand above the protective grille over the fan blades when
the fans are on to get an idea of the wasted air movement. It is
a worthwhile step to consider replacing this grille with a solid
material and then look to adding some side cowling to help direct
air through the radiator core.
Activating the fans. The switching of the fans is something
where some small additional improvements can be made because leaving
the start of fan operation to when the thermostatic switch is activated
means the coolant temps will already have reached 90oC with the
standard MGBGTV8 thermostat. An 82oC stat should be used. The RV8
by comparison has an 88oC stat and the cooling fan is not active
until coolant temp has reached 108oC and doesn't switch off until
temps drop to 100 degrees. Both models can benefit from a manual
override switch added to the circuit so that driver can anticipate
when best to start the fans when it appears slower running in traffic
or a queue is ahead, rather than wait for the coolant temperature
to reach the thermostat switch on point.
How hot is the engine? It seems some V8 owners are chasing
cooling problems based on the temperature gauge readings. Before
delving deep into the cooling system and your pocket to change all
and sundry, do get corroboration that the engine is in fact running
hot. The cooling fan thermostatic switch is one form of corroboration
as it is independent of the gauge. Another is to use a separate
temperature gauge and here I often use a temperature probe on a
I will finish my cooling suggestions with a reminder to ensure that
the engine is set up to the optimum tune as an efficient engine
makes more power per pound weight of fuel used and as fuel burnt
means heat generated less fuel used means less heat generated.
See also V8NOTE288