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MG MGF Technical - New to MG's (heating problems)

Good morning everyone.
I have recently (in last two weeks) bought a 92 (R) MGF 1.8i (that's about as techie as it gets at the mo ;o)

I knew it had a cooling problems (it boiled when I took it for a test drive), the girl I bought it off is a friend and took it to a local garage (who couldn't find a problem and just gave her some rad flush), she never really took it above 80MPH.

So I have taken it to an MG garage, they are having difficulties finding the problem and was wondering if anyone here may have any ideas.

Problem, the car runs fine, as soon as you go above 70 MPG it runs very hot, boils the coolant and goes into the red on the gauge. tends to run OK under this.

The garage have taken it out on a test drive and it runs hot when they get it to the same place each time.

So far, they have:

Checked the head gasket (with a pressure test I believe) this is fine.

Replaced the heat sensor.

Flushed the coolant and replaced.

There was a build up of Gunk from the above, so, have now flushed again and replaced the radiator.

Checked the fan, this kicks in at the right temperature and they thought it should have two speeds, then found out it is just one speed.

The problems still exists, they are now going to take the head off and check the gasket etc.

They have informed me it's when the collant gets up to 104 degrees.

Anyone got any ideas? It's a fantastic looking car and I wanna get out and drive it :o)

Many Thanks in advance for any help I can pass on

Garfy x x
G.D. Williams

1st Action. Have you replaced the expansion tank cap ?? This is the black/yellow cap under the grill flap to the right of the boot lid.
These stick preventing build up of pressure in the cooling system.
Geoff F.
G. Farthing

2nd action. Water pump not moving the water around the cooling system.

TH
Tony Harrison

A compression test should identify whether it is a gasket leak that is over-pressurising the cooling system, plus this would usually allow coolant to leak back into the cylinder when the engine is left to cool.

As Tony suggests, a water pump failure could also explain the behaviour. They're fairly cheap and not too difficult to fit, so I'd suggest replacing that first, before going to the lengths of unbolting the head. Having said that, a repeatedly overheated K series head really ought to be checked for flatness & heat damage, so a new gasket would be a good peace-of-mind once the underlying cause is identified.

A cracked cylinder liner could feasibly give those symptoms too, and is hard to detect without dismantling the engine. If that's the case, a secondhand engine is probably the better option.
Mike Hankin

How about air locks in the cooling system? I've never had to bleed mine so far, but reading Roger Parker's article in the magazine shows just how tricky this can be. Don't, whatever you do, drive the car when the cooling system isn't working properly. The K-series engine can be wrecked by overheating.
Mike Howlett

Mine (98 mgf) was doing the exact same thing, i changed the radiator and it cured it, symtoms were the temp gauge shot up to halfway from cold very very quickly, was ok running round at 50 - 70 mph as soon as you gave it some or were stuck in traffic it started boiling its nuts off, you can look through the grilles at the front and it looks fine but as soon as it was in the air and you you could look properly from under the car it was shot, when it came out there was only a third of the cooling fins left, as soon as it was replaced it cured it, also take a look at the coolant pipes that run the full legnth of your car they may appear ok but dont take that as gospel, might be an idea to change them as well, both easy jobs and if you can DIY the job a new rad and a new set of coolant pipes should set you back no more than £200.
S M Renwick

Thanks for the advice. Changing the radiator has made no difference. They have tested the coolant and it is pumping around the system. The MG garage has performed two headtests which shows no problems. There is definately pressure in the cooling system. The engineer is now stumped and can only suggest removing the head and sending it away for testing.
I am very lucky in that all the work done up until now, I have only been charged for parts as they haven't rectified the problem.
Not sure I could afford it if they hadn't done this.

Thanks again

Garfy2 x x
G.D. Williams

Repeating from what I heard from a friend some long time ago... (probable inaccuracy after being repeated thru two no-technical people and then cleaned up by me)

Apparently the water pump can loose the impeller on the pump drive shaft as they are made of dissmiller metals, this works fine untill the engine gets hot enough for the loosing, but of course disappears as a fault when it cools down again.


Other than that, the impeller at speed could be causing air bubbles which build up in the head - are the bleed valves working right?
Will Munns

No, you are right Will. Roger Parker showed a picture of a water pump with a failed impeller in the MGOC mag a few months ago.
Mike Howlett

Much cheaper to change the water pump than take the head off.
Ken Waring

Thanks Will & Mike, I passed this info to the mechanic and he's going to look at it.
Any idea's how you could test for this fault if it's only when it gets up to a certain temperature?

Cheers

Garfy
G.D. Williams

If he's got the pump off then replace it, the labour is the expensive bit, then boil it on the stove and see if the impeller goes slack.
Will Munns

Fanx Will :o)
G.D. Williams

GD,
A bit of a long shot if you are still chasing those symptoms, but is the jiggle valve ball seating correctly/present? I was having this exact set of symptoms described by my local brilliant independant garage yesterday re an R reg which he finally traced. HTH,
Charles
C.R.B. Simeon

>> Apparently the water pump can loose the impeller on the pump drive shaft as they are made of dissmiller metals, this works fine untill the engine gets hot enough for the loosing, but of course disappears as a fault when it cools down again. <<

Yup, I've heard of this happening too from another source :o)
Rob Bell

Fanx everyone for your suggestions, I have passed them on to the mechanic and he has ticked off all the one's he has checked for. I think we are now down to removing the head and sending away for pressure testing. Hoipe I got the money to cover it all ;o)
I will let you know if/when we get to the bottom of it all

Fanx again

Garfy
AKA Worried from Corby :o)
G.D. Williams

Do you mean hardness testing the head Garry?

Fingers crossed that it works out for you. :o)
Rob Bell

This thread was discussed between 17/03/2007 and 24/03/2007

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