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MG MGF Technical - HGF

I have studied every HGF thread but haven't come across a problem like mine. It's a 2004 TF owned since new with 73k on the clock. The improved head gasket was fitted professionally at 43k as a precaution as I expect to keep the car.The car runs smoothly, there is no oil in the water, and no water in the oil. According to the temperature gauge it doesn't overheat. Up until recently the water level has been as it should but now after use it rises and stays at the higher level long after cooling down. I have bled the system so often (using all 3 bleed points in the recommended sequence) that there is no antifreeze left. I have also replaced the pressure cap and am confident that it works properly.
Today after a fast 60 mile run I left the engine running and opened the boot with the spare key. The reservoir was full to the top and was bubbling away like the inside of a kettle.
Is there anywhere other than the head gasket where so much air can enter the system, and if not, should I bite the bullet and have the head removed?
Any advice that I can pass on to the garage would be greatly appreciated.
W.J. Sheldon

Just wondering how you got on with this problem.It does sound like combustion gases are getting into the cooling system possibly from a failed gasket,you could get a sniff test done to check if gases are present.
AS Douglas

Is the water all nice and clean and blue or pink or is it horrible and gungy . If its horrible and gungy then something is getting into your water and its an HGF
b buick

The head gasket can fail in many ways, waterside to external, usually on the exhaust manifold side, water to oil internal and combustion gas side to water, also internal.
Your local radiator repair shop should have hydrocarbon gas detetection equipment to analyse for combustion gases in the coolant.If so, a combustion chamber fire ring on the gasket is leaking, or the head is cracked[unlikely]
Rebuild with the latest multishim head gasket, new bolts and improved oil rail[ the sump will need to come off for this],all available from Land Rover as they were never used on the mgtf[unfortunately].
The cylinder liner height above the block must also be verified to be in spec[approx 2to 4 thou.proud]
Good luck.
TONY FREW

Sounds like combustion gasses leaking past the fire ring. This is seldom due to HGF, but to other factors, so simple replacing the gasket won't help.

Check the liners have the correct protrusion, that the ead is hard and not soft (thus allowing the fire ring to press into it and reduce the clamping pressure) and that there is no sign of corrosion pitting or porosity where the fire ring makes contact. If any of these conditions are present it is not the gasket that's failed. Causes are:

Liner(s) sinking - some blocks were not machined cleanly on the liner seat, with chatter marks present (see photo). Over time the peaks of the chatter compress and the liner drops.

Soft head: from a previous overheating incident. It is a very common mistake to simply reface the head to remove the grooves made by the fire ring without doing anything about head hardness. This is an open invitation to a repeat episode.

Corrosion pitting: cause by under-strength or incompatible antifreezes.

Porosity - presumably a casting defect when the head was made.

Both these latter two need be present in only a very minor way to cause a problem. The naked eye won't detect it (well, not for old farts like me anyway) so use a magnifying glass.
see second photo.


Paul Walbran

Second photo shows very minor corrosion/porosity (a pair of tiny dots in the centre of the fire ring landing area adjacent to the green blob), yet there is a clearly evident gunge trail where the combustion gasses were leaking.
BTW the symptoms of this engine were exactly as you describe.


Paul Walbran

I'd try giving all the head bolts a quarter of a turn
Paul Hollingworth

My car has similar problems, in addition to yours mine holds pressure in the cooling system for a couple of days,misfires on start and smells of coolant and produces steam from the exhaust all pointing to the head gasket leaking combustion gases into the cooling system and also allowing coolant into the cylinders.

I did 2 sniff tests to see if combustion gases had got into the coolant it they proved inconclusive.

I have now removed the head and can confirm that coolant had been entering the number 2 cylinder,the cause of the failure was indentations in the head by the fire rings and some pitting on the fire ring area,the annoying thing is that the head gasket had been replaced by a mechanic some 6000 mile before I bought the car and began to show signs of failure after about 1000 miles in my ownership, as Paul rightly says simply changing the gasket is inviting trouble had the head been checked and prepared correctly the gasket would not have failed so quickly.

The head needs a light skim at the very least I will get the engine machine shop to pressure,and hardness test the head as I do not intend to do the job again.

AS Douglas

Indentations invariably mean a soft head. It can be reclaimed by peining the fire ring area to compact the head, it brings it up quite well if properly done.
Paul Walbran

This thread was discussed between 11/07/2014 and 21/11/2014

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