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MG MGF Technical - Coolant/Head Gasket problem = Water Leak - Help !!!

Having a problem with an "S" reg MGF

When the engine is warm and you're idling in traffic, the coolant is being forced out of the expansion chamber.

The car isn't overheating because the it doesn't feel too hot and the fan isn't coming on.

Rover say that it needs a new engine and that this is a common problem !!!

The car is now with an independant garage where they are investigating, to date they have (and i hope i get this right) crack tested, removed and skimmed the head and re-fitted with modified gaskets that Rover supplied, all temp sensors have also been replaced ...........still the problem persists.

Does anyone have any ideas?

Thanks

Laura
Laura

This sounds like an expansion tank cap fault, new one is about £6.00 and available from MGR or Halfords.
Unfortunatly I guess it cannot be this if you have had all the work done and it should be the first (and cheepest) thing to check.

Will
Will Munns

Have they done the simple expedient of changing the expansion bottle top?

On "earlier" cars, it was a frequent problem... You can be pretty sure it HASN'T been changed if it doesn't have a white dot on it...

Also print out / show them:
http://www.mgf.ultimatemg.com/hgf_diagnosis.htm
(from Rob's http://www.mgf.4mg.com/ site)

Neil.
Neil

I do hope it ISN'T the expansion tank cap - though that is exactly how it sounds. If it is, I'm afraid you've been seriously ripped off. You must be loking at, what, a £700 bill so far?

E
Ed Clarke

I have to say, the first thing that came into mind when I saw the post was a failed expansion tank pressure cap.

I *presume* that this has already been ruled out. If the coolant system has become pressurised because of a head gasket fault, then checking the hydrocarbon content of the gas contained in the expansion tank should confirm this problem. If the head gasket has failed, forcing exhaust gases into the cooling system, then the gas in the expansion tank will contain hydrocarbons- readily detected with an MOT exhaust gas analyser. If clear, then this is not the problem.

We need to get a clearer idea of what checks have been made, and what additional problems have been identified when the mechanics have performed their investigations.

Keep us posted Laura
Rob Bell

What is the deflection on your engine (water) temp gauge?
Jon

Ed,
it is quite possible that the work done was needed once the car had been got to the garage, so even if this is the problem they may not have been ripped off.
Rob, I thought that, but then they have just had the HG replaced...

Another thought, is water being pushed around the system? (should see it being squirted into the expansion tank with the engine on) if not then the problem could be that the water pump has failed and the pressure waves caused by the coolant boiling local to the engine is pushing the coolant out.
Is the coolant half way down the tank (at about the seam level) over filling could cause this

Will
Will Munns

Ok guys, i have found out some more answers to all those questions !

1) Yes the expansion tank cap has been replaced, thankfully it was done first !

2) Yes the water bottle has been replaced, as the cap.

3) There are no HC's in the gas in the expansion - that was also checked

4) The temp guage always reads normal and the sensor has been replaced just in case

5)The water pump has not failed as water is moving around the system fine


.....the garage man has said that another Rover has been in with a similar problem and they have bled the system in a different way and it seems to have solved the problem..........is this a likely answer !?

Thanks for your help

Laura - Knew i should of stayed with my trusty Golf GTI !
L JENKINS

Next suggestion:

Get them to pressurise the cooling system (they're probably got a pump that fits onto the coolant bottle for the purpose).

Leave it overnight, putting paper/card under the car so that it will show if there's an "external" leak.

After a number of hours disconnect the low tension (12V) supply from the coil/ignition module (so the spark plugs won't fire) and turn the engine over.

Remove and check the plugs: if any are wet, then you've (still) got what is a more unusual Head Gaskit failure, from the cooling system into the cylinders. Pink discolouration of a plug also indicates antifreeze being burnt in small quantities.

(our Astra had this kind of failure last summer - and this is what showed it up - the symptoms were similar to yours...)

However.... if they've already removed the head and replaced the gaskit, it shouldn't still be doing it....

Have they checked the "jiggle valve" in the cooling system byepass? I think that you can get an airlock if it sticks closed... (someone else will answer me, I'm sure!). Get them to check it (or even remove it - supposedly they have "gone" from later engines)

Neil.
Neil

>>Have they checked the "jiggle valve" in the cooling system byepass? I think that you can get an airlock if it sticks closed... (someone else will answer me, I'm sure!). Get them to check it (or even remove it - supposedly they have "gone" from later engines)<<

Hah - I see we are all thinking along the same lines (eh Will? ;o) Neil, I was wondering this too. I guess it is entirely possible that an air lock could cause serious problems with water flow. The jiggle valve is there to ensure that the air returns safely and escapes without causing damage to the expansion tank. There is some info on this provided by Roger Parker and collated by Dieter on his web site - look for references on HGF and bleeding the coolant system.
Rob Bell

Check thermostat and radiator ,the rad can loose efficiency due to 'loss' of cooling fins this will cause o/h symtoms. HTH
Mike.
mike

Sounds like an airlock in the cooling system. As the trapped volume of air expands with engine temperature, it compresses the volume of air above the coolant in the header tank and eventually forces the coolant out through the cap's valve.

An efficent way to bleeding/filling the system is to fill it through the jiggle valve in the cylinder head. Jack up the rear of the car an open the bleeding points in turn starting with the radiator.
Jon

This thread was discussed between 29/04/2002 and 01/05/2002

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