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MG MGF Technical - Oil in Coolant Header Tank

Hi All,I recently purchased a 98 VVC, when the car has been standing overnight and the water level is checked there is a small oil deposit floating on the top of the water,when started it quickly disappears,when I viewed the car it had been started and was slightly warm,no oil was in the tank,the head was skimmed and the gasket replaced approx 4000 miles ago.I'm hoping that it is old oil from the HGF,I intend to drain,flush,and refill the cooling system,
1 What, if any flushing product would be best to use?
2 If the head gasket has failed why does water not get to the oil?(or will it eventually!!)
3 How long would the car run for like this?
The engine oil is clean, no mayo,and the level has not dropped,
The car was not expensive and drives very well I dont mind replacing the head gasket if required,any comment would be appreciated,
Thanks Andy
AS Douglas

Hi Andy. Reading your post in it's entirety, I'm inclined to go along with your initial thought that inadequate flushing at the time of the original HGF is the cause. The lack of any mayo on the dipstick tends to support that theory, but is not a 100% guarantee. I'm assuming that the coolant level is not dropping - only because you don't mention it?!!

To answer your specific points:

1. I can't recommend any particular flushing agents from personal experience, but any proprietary products from reputable manufacturers should do the job.

2. If the car is suffering HGF then more often than not the water will get into the oil.

*If* it is HGF, then to answer your 3rd point it will certainly get worse over the miles eventually enveloping you in clouds of steam and on to the back of a tow truck.

Personally, I'd keep an eye on the coolant level and check for mayo on the dipstick until such time as it can be flushed. You MUST ensure that the coolant system is bled properly after refilling - there's stacks of information in the archive and on other sites about this.
Mike Hall

Thanks for your quick reply Mike
The coolant level is static,warms up as it should,cooling fan and engine bay fan both switch on and off,coolant temp.gauge is always just under midway,the oil temp gauge under reads a common fault I understand.
In short no cooling problems
AS Douglas

I agree with Mike - the original diagnosis is likely to be the correct one - some residual oil residue from the previous HGF. No recommendation with regard to specific flushing agents either - but it can be a devil of a job to clear...
Rob Bell

Washing Powder...... :-)

Put it in the cooling system and do quite a few miles, drain and flush and flush oh and flush.... The refil with 5.25Litres of the correct OAT Anti-freeze.

M T Boldry

Mighten a clothes detergent be a little corrosive to alloy castings? IIRC, quite a high salt content.

In any case, flush, flush and flush again is the name of the game here...
Rob Bell

used dishwasher tablets on mine run it for a few miles and then flushed repeatedly and put in water wetter paranoid now lol
tg hardwick

I removed the header tank draining it from the hose on the bottom of the tank,gave it a good scrub out with hot water and dish washing liquid,that has made an improvement,but I suspect some oil will be trapped in the high points of the cooling system,so it will be flush an flush again,I'm very loath to use any chemicals to flush the system as I dont want to loosen any deposits that could clog up the radiator, I'll report back when Iv'e done!!
AS Douglas

Hi Finally got round to to flushing the cooling system,the car has done approx 2000 miles now since I bought it, no problems at all with the cooling system,engine oil level not moved,no moyo,so its a safe bet that the contamination in the water has been left over from the previous HGF! I drained flushed refilled and ran till the cooling fan come on, allowed to cool a bit drained the coolant then when cold flushed with clean water and refilled again,I did this 5 times making sure it was well bled before starting,I even checked the "jiggle valve" on the inlet manifold,each time the engine came up to temperature and the cooling fan operated as it should with the temperature gauge sat just below mid position as normal.I then filled with anti freeze topped up with water bled the 3 points and started up as before I bled again during the warm up all seemed fine,then the temp gauge rose very quickly engine turned off and it would appear that the coolant was just starting to boil,allowed to cool topped up about 2 pints!!bled again ran to temperature no problems.I am now very worried that I could have caused damage by allowing it to overheat, although it was caught very quickly,as yet it is not showing any signs of HGF.Just shows how easy on air lock can cause problems,I'll report back soon!!
AS Douglas

I realise that checking for oil in the coolant is a useful check on head gasket condition, but. If a few cc have got in there and escaped being flushed can it do any harm?
Stan Best

If you've got the cash, get it done anyway, replace it with the uprated gasket with metal dowels.
I had this done, full service, cam belt, water pump and hose change for 600 (cash!). This was at the Midland Engine Centre in Wolverhampton. They are a small company, do taxi engine repair contracts etc and do things like this on the side. Did a good job, although I will get proper engine flush and oil change done next year.
Martin Costin

This thread was discussed between 16/07/2010 and 17/11/2010

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