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MG MGF Technical - HELP! Before my wife goes mad!

Hi Folks, really need a bit of advice so I can get my wife back into her MGF.

We had a sudden coolant loss after being in heavy traffic. After topping up the header tank and bleeding the system we ran the car whilst in the garage, after some time the water in the header tank started to boil and be released via the header tank cap. The radiator fan did not come on. I have checked the radiator fan by removing the ECU temp sensor while the engine is running and the fan runs ..... I thought it may be a fault with the sensor so I have changed this but the result is still the same, the coolant boils and the fan does not come on?

Any help would be appreciated.

Thanks.
Rob Parry

air lock? The fan didn't run in mine and I had a similar coolant loss in traffic. Dieter had me check the fuse for the fan (to be found in the engine bay). It had blown and was replaced with a 20A fuse. However, if your fan is working I imagine this is all intact.
Leigh Reid

thanks for advice Leigh... have checked all 3 bleed points and water running freely... really am confused with this one!
Rob Parry

Is the water pump circulating the coolant all the time? The impellor can be loose on it's shaft and work a bit when cool, but then pump less as it warms up.
I imagine you have observed the return feed into the expansion bottle. Is it still - and are the rad pipes at the front a markedly different temperature - when the bottle contents are boiling?
Charless

Try a new cap in the header tank. It should keep the pressure in the system and prevent boil over. They are notorious for going wrong, best changed annually in my opinion. You can probably get one from Halfrauds before they shut today - about £5.

Jeff
J Lennon

Both pipes are hot when water starts to "boil"... Cap was changed about 3 years ago the water bubbles in tank and releases out through top of cap. Temperature gauge reads normal but cooling fan doesn't cut in.... Could thermostat be causing a restrictive flow of water??
Rob Parry

I still think it's the cap (especially as it's 3 years old).

Jeff
J Lennon

Have to agree with Jeff. After literally weeks of issues last year (following an HGF repair) the dealer finally fixed it all with a new cap :o)

I now always carry a spare!
Mike Hall

Thank you all for your advice ..... I will get a new expansion cap in the next couple of days and let you know how I get on.
Cheers
Rob Parry

Hi all, I have fitted the new cap this evening and all is working well!
A big thank you to you all, the wife will have her car back :-)
Rob Parry

Good to hear that's all it was Rob. Make a diary note to replace your new cap this time next year, regardless of it's condition.

As you've lost coolant and topped up, perhaps with water (distilled is best), you will have diluted the 50-50 mix of anti-freeze. Frosty weather approaches!

A/F looses potency every couple of years for Glycol and double that for OAT - but don't mix types else the A/F element turns to jelly. Use one or the other and if in doubt which is which, flush the system very throughly and then drain out. Fill with your preferred type half and half distilled water and A/F by volume (10.5litres overall in a dry system) and bleed from the three points. Bleed once with the engine end higher and once with the radiator highest. Best to use wheel ramps or you can drive onto a pavement or some wood planks to achieve this.


Jeff
J Lennon

Either replace, or keep a spare in the boot :o)
Rob Bell

This thread was discussed between 03/09/2011 and 08/09/2011

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