Terry Cox Oxfordshire United Kingdom (eMail) on 29 November 1999 at
15:07:25 (UK time)
Updated by Dieter due to new know how from after Terry
wrote this article. (dated 2006)
There have been many concerns posted with regard to MGF overheating with
the cylinder head gasket (CHG) being the top reason for concern. What
follows is intended to be as complete a picture as to the causes, cures
and preventative actions as I can muster.
The key factors for initial overheat are:
Proper initial system bleeding.
Incomplete bleeding following previous coolant drain down. Each vehicle
has a different procedure which must be followed. There are various bleed
screws which must be opened until coolant flows freely with no bubbles.
Most importantly the filling and bleeding should take place with the heater
set to fully hot. Further the vehicle should be driven for a short while
to release any trapped air and re-bled.
Auto bleed valve blocked
This is situated in the inlet manifold coolant stub pipe - manifold to
expansion tank) . The idea is that the valve will be open to the passage
of air but that water will lift the valve and close it. Blockage of this
will not only hinder bleeding following previous coolant drain down, but
also allow air pocket build up during future use. This may be from small
pockets of air or bubbles clinging to the coolant jacket surfaces that
will migrate during running. There may also be slight combustion gas leak
(having passed the head gasket fire ring). The bleed valve is not available
as a separate item, but is a simple device similar to the "Jiggle"
valve often seen in thermostats. The only way to ensure that it is clear
is to remove the manifold and flush through the stub pipe. At the same
time ensure that the hose from here to the expansion tank is also not
blocked or kinked.
You MUST have antifreeze in the cooling system all year. Only recommended
antifreeze specification must be used and you should not mix types. Antifreeze
not only contains Ethylene Glycol, which lowers the freezing point of
the coolant, but more importantly, special additives which prevent corrosion.
This is especially important with aluminium engines, where unprotected
aluminium will rapidly corrode, especially where it is in contact with
other metals. This not only results in erosion of the aluminium surface
in critical areas, but also potential perforation and coolant loss. Additionally
the displaced corrosion products will block the radiator. Engines stripped
for examination have shown areas of metal erosion to the cylinder head
face. This is especially seen at the CHG fire ring location and also adjacent
to the elastomeric track. This is caused by lack of proper inhibitors
in the coolant. Leakage is likely to occur at these points.
The result of age or previous overheating can both degrade the antifreeze
capability of the coolant but more importantly the corrosion inhibitors.
Therefore antifreeze should be replaced at the recommended frequencies
and in the event of previous overheating. You can be sure that the cooling
system of your vehicle has been designed to operate properly using the
designated approved coolant. It should not need adjusting or modifying.
There have been suggestions that a water wetter product may be used (http://www.redlineoil.com/wwti.htm).
This product does not contain any antifreeze properties but does include
an additive pack which claims to work well. The benefit is that Ethylene
Glycol has a lower thermal conductivity than water and inclusion in the
system reduces the overall conductivity. It appears that the benefits
are mostly from this and gives very little benefit when used in conjunction
Proper operation of radiator (and where applicable engine bay) fans.
These have been known to be wired in reverse and spin the fan the wrong
way. You may also check wiring connections and the sensors that activate
No blockage of radiator (leaves etc.). Check at old MGF for correct front
fan fuses. They got changed from 15Amp to 20 amp in Y2000.
See also comments under anti freeze. Remove any external blockages and
thoroughly flush the cooling system.
Proper operation of thermostat.
Generally a very reliable component however, overheating may damage the
thermostat. It should therefore be replaced after overheating.
Proper operation of radiator pressure cap
Now usually on the expansion tank. There have been previous entries on
this where problem caps could be identified with the dimple in the cap
being offset. A faulty cap may result in low pressure in the cooling system,
effectively lowering the boiling point of the coolant.
General Cooling System Leaks
Obvious, I know, but do ensure all hoses are in good condition and firmly
clamped. Look especially for chafing of hoses. Also check the metal pipes
for corrosion perforation (especially the one at the back of the engine
coming from the thermostat).
Key factors on repeated overheat situations
Cylinder head condition.
Previous over heat can result in the aluminium softening and the steel
fire rings in the CHG burying them selves into the head face. This causes
the clamping of the gasket at the fire ring to be less than required and
combustion gasses to pass into the cooling system. This not only applies
excessive temperature to the elastomeric sealing track on the CHG, degrading
it, but also introduces gas pockets in the cooling system reducing it's
efficiency. Even skimming the cylinder head to remove the impressions
may not fix the problem if the aluminium has softened.
Cylinder liner stand heights.
Should the liners shift due to relaxed clamping, then they can hammer
down on the location face in the cylinder block. This mushrooms the location
resulting in the liners sitting lower. This again results in a clamp load
at the fire ring that is less than required. Rover do not quote the liner
stand proud in publications as they cannot be adjusted (shims etc. not
permitted). Actual stand heights depend upon the age of the engine. It
is either 0 to 5 thou or 5 to 9 thou. (MGFs would all be 5 to 9 thou).
It is felt that 2 thou should be the lowest for good results. In any event
they should all be within 2 or 3 thou of each other (The correct liner
height is 4-5 thou (0.1mm to 0.125mm).). If you have problems here, only
a new engine will fix it. (It has been known that Rover have got this
wrong at original manufacture).
Cylinder head torque
This is key. The spec is 20 Newton meters plus 180 degrees plus a further
180 degrees. These need to be progressively applied, that is all the bolts
to 20 Nm, then all bolts 180 degrees etc. It's ever so easy to miss the
second 180 degrees or to miss bolts. Always follow the torque sequence
and don't get side-tracked during the procedure. Also be very careful
fitting the head to the block. If you leave the manifolds on (which is
common practice) the head is unwieldy and the edge of the head can be
bumped on the gasket track damaging it (without you seeing it). It will
Inlet manifold gasket condition (plastic manifold)
This is sealed by a polymer gasket fitted into a recess. Engine overheating
is known to degrade the material. This results in water loss (at either
end of the manifold) and further problems. Rover have introduced a gasket
in an improved material which will withstand a higher temperature though
as far as I can see the gasket only deteriorates if overheating has occurred
(not being the cause of it). There have been problems of the manifold
fixings loosening also. Be sure that this gasket is always replaced after
The causes of overheating are many. When the cylinder head gasket is removed,
this shows clear signs of this where the elastomeric track has become
dislodged, gives the appearance of melting or taken a compression set.
Although this results in water loss, it is the symptom rather than the
cause. You should be sure that the root cause for the overheating is established
The MPI, not VVC has the plastic inlet manifold and was built
before VIN 504633 with a black coloured gasket the new one is green coloured.
Part Number GUG704094MG
New designed hollow steel dowels and re-designed
gasket since the beginning of 2001 for centering of the block, gasket and
head. Done by factory since Model year 2002, so app. from VIN 527xxx upwarsds
Update in December 2001 reported by Mike Satur to the MG Cars BBS. The stretch
bolt thread length importance is known, but the thread sump depth in the
block was found as probable trouble on a MY2000 car (location between cylinder
3/4. See his instructions
to check the depth at a dismantled engine.
2006, January 31.
Land Rover introduced a new design Head Gasket (MLS)
and Oil Rail to improve the engine and decrease head gasket failures.
2008, March. X Part introduced the
MLS gasket kit including oil ladder for K-Engine repairs. Kit made for
120bhp engine. The different gaskets for a VVC repair need to be bought
history @ Rob
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