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MG MGF Technical - Overheat at tickover

Hoping someone can help me - I've had my 2001 VVC F in the garage over winter while I've been away, and while it was running fine in October it's developed a complaint of some sort since - it overheats if left at tickover, to the point of the expansion bottle boiling over. Took it for a long drive and while it's moving the temperature settles to normal, but within 30 seconds of coming to a standstill the gauge starts climbing. Holding the revs at 3k stops the gauge climbing any further, but it doesn't start dropping again until the car gets moving again. Replaced the expansion bottle cap, didn't make any difference. Not sure if the engine bay fan is operating, but the radiator fan is, not the moment the gauge climbs but soon after. So, what's next?

Thank you in advance
James

Sounds as though the rad is partially blocked, when engine up to temperature see if radiator has uniform temperature across the matrix.If not change it and flush out the system.
mike

I would suggest the radiator coolant fan is failing to come on.

When your car is at idle, stand at the front and listen out for the fan kicking in. If it doesn't and the temperature needle makes a dive for the red, then the fan is the problem - and not an issue with the radiator that Mike suggests.

If the fan isn't kicking in as it should, you need to determine whether the fuse is at fault (there are two to check) or whether the problem lies with the engine manangement's water temperature sensor. My car's been through 2 or 3 in 10 years - so it is a fairly common fault...

See http://www.mgf.ultimatemg.com/group2/common_problems/hgf_pages/related_problems_overheating.htm for more on how to diagnose rad fan non-operation...
Rob Bell

<Not sure if the engine bay fan is operating, but the radiator fan is, >

Maybe something simpler like restricted airflow thru' the rad. Thirty seconds is a very short time to see a temperature rise, mine runs for several minutes before a noticeable rise at this time of year. This tends to indicate coolant flow problem rather than airflow.
Ken Waring

James - apologies - I didn't read that bit about the rad fan coming on!!!! D'oh! (_8(I)

Are the rad pipes getting warm? They're under the washer fluid bottle - just remove the front bulkhead shroud and it is easy to get to. Both should be getting warm - and if this is the case, then the radiator is suspect. If they're both cold, then the thermostat is suspect - or there is a fluid lock somewhere there ought not be...
Rob Bell

Thank you all for your help. I considered the radiator having clogged slightly, but couldn't see how that could happen just from the car not being used. It looks in fairly good condition externally, but I suppose that doesn't mean much. I'll check the pipes when I get home tomorrow.

Would the overheat when it boiled over have cooked the head gasket or the cylinder head? That's my main worry, I stopped the engine when I saw the steam but with hindsight I probably should have just driven it until the temperature dropped, hard to say how much coolant escaped but it wasn't much of a puddle. Lots of steam though 8-(
James

Radiator corrosion is another killer of radiator efficiency - and a common cause of coolant leaks- see Dieter's webpage: http://www.mgfcar.de/radiator/radiator.htm !!!

This could occur on a car that has not been used much, although in your case, it doesn't seem to be the case, as you've inspected the rad (did you remove the bumper? It's the only way to get a good look at it).

Regarding the gasket - you'll probably get away with it if the overheat wasn't for too long.

If you get stuck like this again, put the heater to full heat and run the fan at full speed - it makes for an astonishingly effective radiator in its own right!
Rob Bell

I did the above, putting heater on full blast when my old car overheated and it got me home in traffic without the bother of stopping many times.
Only when the heater blew cold air did I stop cos at that point the coolant level (mostly water with a bit of anti-freeze) was so low that any further running would mean engine death.
Good to know I can do the same in the mgf.
KS Gould

This thread was discussed between 03/04/2006 and 04/04/2006

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