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MG MGF Technical - MGF Coolant Boiling away

Hi.

I just drove from Leeds to the South Coast and the car seemed fine. Its a 1997 MGF, that had Head Gasket done a few months ago.

I stopped after about an hour to check my coolant level (I have been losing coolant through a leaky radiator which I believe was 'radwelded' shut), and it was fine, except that the reservoir was steaming quite vigorously.

I left it to cool some, checked the level and set off again.

As I came off the motorway, this is after a good 3 hour run at speed, again I had the same steaming reservoir, only this time I think I have lost most of the coolant.

The oil and water guages were normal all the way down.

Any thoughts anyone ? Why would stopping/slowing down cause this sudden coolant loss from the reservoir ?
HC Jones

Have you replaced the radiator? If not, chances are the leak is a result of excessive corrosion of the cooling fins, which means the cooling ability is minimal. Perhaps at speed the airflow is enough to keep it from overheating, but the heat is too much for the radiator to deal with at lower speeds. Try removing the plastic shroud around the washer reservoir and checking the temperature difference between the two coolant pipes - one should be significantly cooler than the other, even stationary.

Did your gasket failure allow oil into the cooling system? If so, the sludge that will have created is likely to collect in the radiator, further reducing its cooling capacity. And Radweld type fixes aren't exactly 'recommended' for the K Series engine...

Also, check the radiator fan is operating correctly - this is a common problem, often due just to the fuse having blown, and don't wait for the temperature gauge to show an overheat - it's fairly useless, and by the time it responds you may already have pushed your shiny new gasket beyond its limits 8-/

Lastly, was it an MGF specialist that fitted the new gasket? Many are the tales of woe of repeated gasket failure due to the cooling system having not been bled properly after fitting, leaving air pockets in the system that will if left unresolved cause erratic cooling, and that's more than a head gasket can stand...

bandit

I'd also change the cap on the header tank - about £5. If that's not holding the correct pressure it will allow the coolant to boil. It will also allow some of the coolant to escape and that might be the cause of the drop in level.
David Clelland

Most impressive. You really know your stuff, chaps.

1. Cooling fins ? My radiator doesnt have any. Well, one or two maybe but if you touch them they drop off.

2. Reservoir cap ? Mine was scrounged from a scrapper a couple of weeks ago - the original now being somewhere in the undergrowth at the Tesco forecourt. (*sigh*)

I have good news though, my replacement radiator will be fitted first thing tomorrow morning, and the Head Gasket test showed all ok.

Its a pity in a way because I was banking on 'sorry, officer I have to drive that fast to keep the car cool'. Once this is fixed I will need to be more creative.

All I need now is to fix the handbrake, odometer, tyre, rear windscreen, soft top, blipper and fuse 12, and I can start thinking about the upholstery and paint job.

Is it possible I am falling in love ? I did manage to get 120 out of the old girl a few days ago ...

toot toot
Hugh
HC Jones

This thread was discussed on 01/06/2009

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