MGF Coolant Leaking - White Smoke From Engine Vent

I would be very grateful if someone could give me some pointers.
My 1998 MGF 1.8 VVC had the head gasket replaced earlier this year
(2008). However a couple of days ago I noticed the following symptoms:
+ After driving for about 40 mins, the temperature gauge rises from a middle setting (between Hot and Cold) and starts approaching the red section on the temp dial on the Hot. + White smoke starts to emit from the vents above the engine in the boot area + The temperature gauge seems to fluctuate in the hot zone. Seems to get worse when the car is idle which seems a little odd. + When I open the flap in the boot, the coolant expansion tank is close to FULL but boiling away. Colour is rusty red/green. + Coolant seems to have leaked all over the engine as well - which may explain the smoke + There is no appearance of the white "mayonnaise" type substance on the oil dipstick or elsewhere around the engine/expansion tank which is symptomatic of HGF + Car cools and the above start again.
Many thanks in advance.
-- Shuaib
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snipped-for-privacy@gmail.com wrote:

You need a new cap for the coolant expansion tank. Halfords do them, but be SURE it's the right one.......they have a habit of getting it wrong. It's common fault, so later, get over to ebay and get a couple of spares. For furure help, go here..... http://forums.mg-rover.org/forumdisplay.php?f  Very friendly and helful bunch. If you continue to drive with the bad cap, you risk gasket failure again!!! HTH :)
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Pete C
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Srabbani, I'm concerned you haven't replied. Running your F as it is is a no-no!!! My 'repy to' is valid if you want to mail me.
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Pete C
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Pete, thanks for the advice. Digging a little deeper into the issues particularly around the temp rising when idle, I found the following link on the web:
http://www.mgf.ultimatemg.com/group2/common_problems/HGF_pages/related_problems_overheating.htm
Wondering if this is the issue - the symtoms seem to correspond exactly. Have tested the fuses and both seem intact. Could point to an issue with the ECU temp sensor or radiator. Will do some more digging.
-- Shuaib
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snipped-for-privacy@gmail.com wrote:

http://www.mgf.ultimatemg.com/group2/common_problems/HGF_pages/related_problems_overheating.htm
Unlikely. Coolant cap...............less than a fiver. It's a common and well known fault, the symtoms of which you describe exactly. Go to the link I gave you and ask there. A tenner says you'll get the same answer. :)
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Pete C
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Pete
Will certainly look into getting a new coolant cap. In the meantime can you help me understand why a faulty coolant cap would cause the engine temp to rise to max and also why it would cause the coolant itself to boil in the expansion tank.
Regards
Shuaib
Pete C wrote:

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snipped-for-privacy@gmail.com wrote:

Temp is rising because the coolant is no longer under pressure and cooling. The valve in the cap fails which means coolant boiling at approx 100C instead of around 120C under pressure.
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Pete C
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Thanks - will follow your advice this weekend and keep you posted. Many thanks for the info.
-- Shuaib
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snipped-for-privacy@gmail.com wrote:

Your welcome. Please let me know how it goes :) And join the forum I gave link for.......... costs nowt :)
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Pete C
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Pete - Bought a new coolant cap. Unfortunately, the same symptoms. When the engine is warm and the car is left idle for about 10 mins, the temperature starts to rise towards hot.Coolant bubbling.
Assuming there is a radiator fan beneath the front bumper - but even listening carefully I can hear nothing from this area of the car. Can I assume the ECU sensor or radiator fan is the culprit?
Looks like I need to take the car to a specialist. :(
Regards,
-- Shuaib
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snipped-for-privacy@gmail.com wrote:

Fuses : Under bonnet No.2 Under dash, drivers side No.6 Not sure which of these is rad. fan. Beyond that, I wouldn't like to say. I'd suggest you ask in http://forums.mg-rover.org/forumdisplay.php?f  They are really very knowledgeable people. :)
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Pete C
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Hi Based on the syptoms my guess is a bad head gasket dumping cylinder pressure in to the cooling system.
Don snipped-for-privacy@sbcglobal.nettt
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Okay an update. Took the MGF to Fisher MG specialists (very helpful by the way). The ECU temp sensor was faulty (now replaced) and the connections to the radiator fan were also loose. The car is now A okay - no more overheating. Thanks for all the feedback - all very informative.
Regards,
-- Shuaib
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snipped-for-privacy@gmail.com wrote:

Thamnks for posting back. Glad all is well now. BTW, where Is Fisher ? :)
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Pete C
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They're in Sydenham, SE London.
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snipped-for-privacy@gmail.com wrote:

Thanks :)
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Pete C
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Pete
Will certainly look into getting a new coolant cap. In the meantime can you help me understand why a faulty coolant cap would cause the engine temp to rise to max and also why it would cause the coolant itself to boil in the expansion tank.
Regards
Shuaib
Pete C wrote:

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hi please help. i havent started my mgf 97 for some time i was havingstarter problems.. it was left out doors for some time, so i tried starting it today and when the engine ran there was a bad smell and a lot of smoke came out of the back engine area. when i turned the engine off it was ok but i am very worried now. can any one help me on this one please text 353876459339 liam snipped-for-privacy@hotmail.com
url:http://myreader.co.uk/msg/1276284.aspx
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