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MG MGF Technical - HGF?

My F, a 2001 mpi, 29k, has been losing water steadily and slowly over the past few weeks, I've checked all the usual places, rad, pipes, heater, inlet manifold etc and there's no sign of it going overboard anywhere.
yesterday, the temp gauge shot up to about 3/4, and i noticed steam coming out of the engine cover vent. 'here we go' i thought, but then with a sort of gurgling wooshing sound - not dissimilar to that annoying Kenco ad, the steam stopped, and the gauge returned to normal.
i topped the water back up when it had cooled, and it's been fine since - i know it was yesterday, but i've covered 300 miles since.

there's no sign of mayo in the oil, and the pressure cap was replaced in June.
I suspect a faulty thermostat, but am i right in thinking that the localised boiling in the head will have damaged the head and gasket?

mike roberts

Boiling coolant doesn't always mean HGF, and whilst the possibility it may cause damage does exist doesn't always mean it will.

I've experienced it a couple of times after the car has been driven hard and the engine turned off without a period of gentle use to allow it to cool down a bit first with the coolant still circulating. Mine has a ported head and some hot cams, so I believe that makes it more prone than a standard top end.

I've heard there are a couple of aftermarket solutions involving secondary water pumps which keep the coolant circulating for a period after the engine is switched off. Can't put a URL on any of them off the top of my head though.
Alex T

This all happened on the move though, not as the result of heat soak ..

how likely is it that it's the pressure cap - again?
mike roberts

Similar thing happened to me on the Nürburgring - and the same as Alex I hadn't allowed the engine to cool a little first but the car drove on OK for the next few years.

Anyhow that was about 5 years ago and earlier this year I had a major service done including new head gasket and dowels plus a head skim and the engine specialists reported that there was no damage to the head so only required a minuscule amount of metal removed.

So clouds of steam and water does not always mean HGF.
Ted Newman

>> I've heard there are a couple of aftermarket solutions involving secondary water pumps which keep the coolant circulating for a period after the engine is switched off. Can't put a URL on any of them off the top of my head though. <<

I have an electric booster pump fitted in the same manner as the Lotus heat management pump: http://www.mgf.ultimatemg.com/group2/coolant/ewp.htm

But I agree: boiling coolant doesn't necessarily mean HGF. It's just as, if not more likely to indicate a pressure loss from the seal cooling circuit - be that from the expansion cap (has been a very common fault), or due to faulty hoses, corroded radiator or damaged underbody coolant pipes.
Rob Bell


latest update is that water seems to be disappearing at a faster rate than before, but it's behaving itself otherwise.
no sign of mayo, or leakage out, so i can only assume that it's going into one of the cylinders?

is there any way of confirming this?

Thanks once again,

mike

mike

Another mode of head gasket failure is failure of the fire rings: this allows the products of combustion escape from the cylinders and pressurise the cooling system.

The pressurised cooling system then vents the excess pressure past the expansion tank's pressure cap.

The characteristic of this type of failure is that water loss is directly proportional to how hard you use the engine. For example, on my car which suffered this form of failure, water loss was neglible when pottering along gently. But give the engine some welly, and the coolant level would drop precipitously.

The test to perform is an MoT exhaust gas analyser in the expansion tank. There should be no evidence of HCs or CO in the header tank. If there is, then the gasket has failed... :o(
Rob Bell

thanks Rob,

was the fire ring failure separate to your HGF?

mike



mike

In my case Mike, the failure had much more to do with the cylinder head having gone soft - possibly due to overheating secondary to coolant loss. Consequently, there are deep circumferential rings around the combustion cambers on the head, essentially allowing the fire rings to flap about in the breeze in the space between the liner and the new, indented head surface :o(

Pictures here: http://www.mgf.ultimatemg.com/group1/info/journal/blog/index.htm
Rob Bell

This thread was discussed between 20/10/2005 and 26/10/2005

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