to keep cool under pressure - V8 cooling system
Here Colin Leisk
(Damask 1729) from Warwickshire provides a comprehensive and seasonal article
on maintaining the V8 pressurised cooling system so your V8 does not overheat.
system leaks appear to be a persistent problem with the V8 engine after a few
years service, thanks largely to the massive system pressure of 15psi - about
one atmosphere! Since I replaced the radiator cap on my car some 7,000 miles ago,
as it was not maintaining pressure, I have suffered two burst hoses, a leaking
heater valve, a cracked expansion tank and finally (I hope!!) a radiator leak.
Many of these problems are not confined to the V8 and I hope this article may
also be of interest to owners of other MGs.
does the V8 have such a high pressure? Perhaps the obvious solution is to swap
the radiator cap for the 10psi cap fitted to the later MGBs but this is one I
would not recommend. We all know that increasing the pressure raises the boiling
point of a liquid - in fact water will boil at around 110oC under 15psi pressure.
Normally the temperature on the gauge will not rise anywhere near this point,
and will only reach "normal" in certain conditions such as town driving
when the cooling fans will limit the temperature. This is when the danger arises
from either fitting a lower pressure 10psi cap or a faulty 15psi cap. Although
the temperature at the thermostat may be registering normal, the local temperature
of the water around the hot spots such as exhaust valve seats and ports may be
considerably higher, with a risk of boiling if the pressure is not sufficiently
high, and consequent damage to the engine. The first symptom the driver will discover
is the loss of water through a cracked cylinder head!
localised boiling occurs, heat transfer from the hot cylinder head walls is greatly
reduced hence the casting may overheat, warp or crack. On older MG engines there
is the possibility of an exhaust valve may start to burn out due to overheating.
Needless to say, these risks will be higher with a "tuned" engine, or
if the mixture is set to weak or the ignition too far retarded. The engine in
the Triumph Stag with its long and narrow water passages and lower system pressure
is an example. Long before the temperature gauge registers anything amiss, the
damage is done. The incidence of warped heads on the Stag is quite remarkable,
largely due to driving in traffic in a high gear which the V8 engine is quite
capable of doing. So beware!
look at some of the components of the cooling system and the problems which may
Tthe V8 Drivers Handbook (AKD8423) specifically recommends the use
of Blucol antifreeze at all times. As well as protecting the engine from frost
damage, a glycol based antifreeze performs two other important functions:
corrosion. It reduces the electrical conductivity of the water, so reducing
corrosion. This is the opposite effect to salt! Without Blucol, the water will
start to pick up iron compounds from the steel components of the system, which
will then accelerate corrosion of the aluminium parts - the block, head and pump
housing - by electrolytic action. Moreover the deposits will tend to block small
waterways, reducing the efficiency of heat transfer and the flow of coolant. My
engine needed a thorough flushing with Holts Radflush to remove all the sludge
built up due to a lack of corrosion inhibitor in the antifreeze.
boiling point. It raises the boiling point of the coolant water, so reducing
the risk of local boiling near hot spots. Note the methanol based antifreezes
sold under some well know brands are not recommended. It pays to set aside the
makers' claims and read the small print on the tins. It also seems reasonable
to conjecture that the useful life of a methanol based antifreeze will be reduced
in the V8, since the vapour of methanol exceeds 15psi at 80oC - about the normal
operating temperature of the V8 engine - and will evaporate. However glycol based
antifreeze may be safely left in a cooling system for at least a year.
How can one test the strength
of an antifreeze solution? I found that a hydrometer for measuring the specific
gravity of a battery electrolyte will give a satisfactory indication - flush any
residual battery acid out first! As an example a 25% solution of Blucol has an
SG of about 1.05 which is just discernible on the hydrometer scale. It is then
simply a matter of adding neat antifreeze until this reading is obtained. For
topping up, the best plan is to make up a bottle of coolant with the correct proportion
of Blucol glycol based antifreeze and keep it handy in the garage.
It pays to have the cap pressure tested every year or replaced. A
faulty cap may be spotted when a hot engine is tuned off. As the temperature rises
slightly, and hence the pressure in the coolant system, strange gurgling noises
may be heard in the vicinity of the cap as the steam and hot air escapes. The
cap also has a vacuum relief valve in it to prevent damage as the engine cools
and the water contracts. This may be tested by sealing your lips round the rubber
seal on the cap and sucking! Air should flow in quite readily. (Editor: I think
I would prefer to get my lips round a pint of Hook Norton and buy a new cap!)
It restricts the coolant flow until the coolant reaches the correct operating
temperature when the thermostat opens thereby allowing the coolant to pass for
cooling in the radiator. This allows rapid engine warm up and prevents the engine
from running too cold. It should have a small hole in the frame, normally blocked
by a plastic bead. If the thermostat jams closed, then the
to Contents listing
bead should melt allowing the water to flow through the hole.
is normally opened by the force generated by the wax expanding in a small canister
which pushes the valve open against a spring pressure via a piston rod. To test
this, remove the thermostat from the car and place in a pan of water. Bring the
water to boiling point when the thermostat should open 3/8 inch and close fully
on cooling. When replacing the thermostat, ensure that the arrow points towards
the radiator top hose, and renew the gasket. Note the thermostat acts as a restriction
to the flow even when fully open, so the all important coolant pressure is higher
on the engine side. Never run the engine without a thermostat except in an emergency.
the hoses regularly for signs of perishing or "puffiness" indicating
the rubber is delaminating. If one or two hoses appear aged, it is a sound idea
to replace all eight at once to save problems later. The two heater hoses on the
V8 are reached by unbolting the manifold adapter complete with carbs and air box.
I easily obtained
most of the hoses, the exception being the bypass hose from the manifold to the
pump inlet. This problem was solved with a length of Quinton Hazell 5/8 inch -
4/3 inch flexible hose which is easily bent to suit and is far easier to fit than
the standard "stiff" hose. Our Spares Secretary (Peter Beadle for over
20 years and at the time of this note) has since informed me that the hose from
the Rover SD1 (part number ERC2278 or ERC2279) is a perfect match.
The small hoses from the radiator top to thermostat housing can be cut from a
length of ¼ inch bore hose, obtainable from a rubber stockist. He also
mentions that the L-shaped hose connecting the heater to the valve can be cut
from a Midget heater hose.
you decide to refit old hoses, ensure that the clips are fitted back in exactly
the same position on the hose to prevent leaks. A new hose can be eased into place
with the help of a smear of washing up fluid on the inside. Check the clips for
tightness regularly and keep hoses free of oil to avoid perishing.
valve (BHA5297 or BHA5229)
The valve is made by Smiths Industries but
is difficult to obtain. However the parts are identical to BHA5298 as fitted to
the MGB1800 - the difference being in the orientation of the cable mechanism in
relation to the outlet tube on the body.
valve BHA5298 can be dismantled easily by slightly easing back the claws
round the edge, drilling out the pop rivet which aligns the two halves of the
valve, and gently rotating the halves to dislocate the claws. Next, position the
two halves together so that the assembly will be correctly aligned when the halves
are twisted into place. If necessary, ease the claws open again with a screwdriver
blade before replacing. Push the two halves firmly together and at the same time
twist the valve so that the flanges on the body locate with the claws. Replace
the pop rivet, and tighten the claws with a Mole grip, or by tapping evenly all
round with a hammer. Result? - a water tight valve for less than the cost of the
"special" V8 unit. Unfortunately the rubber diaphragms are not available
for reconditioning the old valve. Reconnect the operating cable with the valve
locked in the "off" position and the control switch "off".
Leaks in the top and bottom radiator tanks or in the expansion tank can be
easily soldered up with the aid of a blowtorch. Use good quality solid soft solder
in solid or coil form, obtainable from a plumbers merchant, and clean the area
to be repaired and apply flux liberally. Carefully apply sufficient heat to the
metal to allow the solder to run into the joint, then build up the solder gradually
without letting it run. Repairs to the radiator cores are a trickier proposition
involving the removal of one or more vanes to gain access to the leak. This may
not be a lasting solution since it is a fair bet that other cores will be sufficiently
corroded to spring a leak in a short time. The experts, such as Serk Services,
will first remove the top and bottom tanks, then clean out any deposits from inside
the cores and finally pressure test the unit after carrying out repairs and repainting.
A completely new
core with vanes is often the only answer. Serk's current cost for recoring the
radiator for the V8 is £51 (less a 20% discount for members) and your radiator
will usually be returned within a day. All work carries a 12 month guarantee -
in all a service which is good by any standards today.
The twin fans are controlled by a thermostatic switch and relay.
Replacement switches are hard to come by though MG agents, Beer of Houghton, had
some when I last checked. Comprehensive information on checking and repairing
the fan motors is given in the V8 Supplement (AKD8468) which will not be
repeated here. No mention is made there, however, of checking the bearings. Obviously
worn bearings will increase wear on the brushes and commutator as well as affecting
thrust is counteracted by an iolite washer with a spring washer to control end
float. Check the action of the spring by pushing the fan blades backwards - the
shaft should move about 1/16 inch and spring back against the trust washer. New
iolite thrust washers and bearings may be turned from bar or tube stock (available
from stockists such as Bearing Services) and the bearings are then pressed into
place in the motor casing and end cap. Having completed a thorough service of
the system, I am at last looking forward to many miles of leak free motoring!
reserved by the V8 Register