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MG MGF Technical - hgf the fact 2

hi all
Posted 23 March 2004 at 04:55:49 UK time
spoke to a mechanic who has done a lot of hgf , he claims its the heat that builds up in the engine bay. He told me that it gets to 110 deg cel here in Oz, which causes the rubber and plastic fittings to get brittle and leak.
Makes a lot of sense as I have just had my car at the dealers for nearly 3 weeks trying to find out where the coolant disappears to. He told me he fits 2 extraction fans at the top engine bay outlets that come on with the engine bay fan to help cool the engine bay down. will be fitting some soon will let you all know if it helps
regards Mike D

M L Dippenaar

Interesting point. I recently purchased a 98 MGF VVC and before purchase tried to get myself fully conversant with the details about hgf. The one I brought had the hg go on the previous owner.

My understanding was that once the hg goes and is replaced with a good after-market one that the problem should not pop up again.

All the same, I'd love to hear how your mod. goes.
J. F. Best

<<once the hg goes and is replaced with a good after-market one that the problem should not pop up again>>

Assuming that the original cause of the HGF has been identified and fixed.

As most people say, the HGF is normally the result of a problem and not the underliying problem e.g. a hose failure leading to coolant loss, a fan failure leading to overheating, poor locating dowels, warped head etc. Some HGFs are, of course, because of a faulty gasket.

There are reports on this BBS of multiple HGFs.

There are reports on this BBS of HGFs within days of car having work carried out on it's cooling system etc.

sprinter @home

Not sure about the extractor fan idea...when they're not running (i.e. most of the time) they will cause a significant drop in airflow and therefore an increase in temperatures! Furthermore, if they startup whilst the car is moving, they will be trying to push air up and out of the vents when, I believe, the vents are actually a low pressure area and suck cold air IN and then through the hollow bootlid and out of vents at the back. The fans would then be fighting air flow and creating stagnant air...

Tim.
Tim Jenner

Tim, air flow through the vents changes depending on whether the car is moving or not and whether the roof is up or down. When up, there is a high pressure area over the boot vents - and this is used to some effect on the MGF Cup car racers; they take their air intake from this location...

However, as Mike suggests, the vents are actually designed to allow air to vent OUT of the engine bay - the natural airflow pattern being under the car, under the sump, up the back of the engine and out through the vents...

However, I agree with you Tim - some thought does need to be given to the fan design so that it doesn't, in fact, IMPEED airflow...

As regard to engine bay temperature as a cause of HGF? I don't believe it is. But point well taken as regard to engine bay component life. To prevent HGF, it would be far better to control coolant and oil temperatures and even out the control feedback oscillations. Remote thermostats and water/oil coolers have a fantastic reputation in Elise curcles for erradicating the HGF problem...
Rob Bell

M L Dippenaar, Tim,

Are you guys talking about the same location for the fans.
Erik

Hi guys, I believe that you could have the fans running all the time if you like as well as when you switch off. will need 2 circuits and a switch inside the car. The reason I believe that the heat can cause hgf is the you can get coolant loss from hose cracks and distorting to expansion tanks etc which can lead to overheating and hgf. My car started loosing coolant suddenly and overheated. we have pulled the head off rebuilt the rad pressure tested too 25 lbs per inch and still we could not find the reason for coolant loss We have pretty hot weather here around 40degs days We now think that the heat causes the the expansion tank cap to vent coolant at at certain temp cause excessive coolant loss and over heating we have now fitted a new coolant tank and the problem seems better. yes we tried 3 new caps with and withot the white dot ( new tank cap is black again) before this and made no difference the old tank was pressure tested and seemed fine untill you drove the car then it lost coolant, any one have a similar problem?
Regars mike
M L Dippenaar

Mike,
have you checked on the health of the pipes to and from the radiator under the car? And was the pressure test done hot or cold, or both? If the pipes are getting old and have split, they may only leak over night when the engine is cold. When it is hot, the pipes expand and close up the cracks, so no problem. Or so my mechanic told me after my Fs pipes needed replacing.

Cheers,
Neil
Neil Courtney

Hi Neil,
The tubes were replaced about 6 months ago as well as the hose clamps. it a sh*tty problem thats starting to cost big money, thank goodness i have a extended warranty the only dealer here in Perth charges about $130 a hour so not cheap .
cheers mike
M L Dippenaar

This thread was discussed between 23/03/2004 and 24/03/2004

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