Coolant pressure

[nib]

My stag runs at the halfway mark on the temp gauge without much change even on fast drives down the motorway and in traffic on hot summers days,the water retuns back to the rad fine when it cools down but last night I thought I would check the water in the rad and there seemed to be quite a bit of pressure and quite a bit of coolant came out even undoing slowly,I hadnt released the pressure cap on the expansion bottle as I thought after my car not being run for a day and half I would have no pressure and also expecting everything to be fine didnt want to lose coolant out of my rad.

Is this normal,as before im sure there wasnt this amount of pressure and the water level use to settle slightly down(about 3/4 of an inch) from top of rad.I am losing no water but a bit worried about this amount of pressure.

This is a Mk2 coolant system.

Thanks for any help.

Mark

[Guest]

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Hiya Mark, it rather sounds as if your cooling system is being pressurisedvia a failing head gasket, i.e. cylinder compression, once the engine has cooled down there should be no pressure at all. Sorry to be the bringer of bad news, but it does sound like it. Martin.

[nib]

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Hi Martin

The only thing that confuses me is that if thats the case I wouldnt have thought the coolant would return to its normal level,I imagined the expansion bottle level would rise even after cooling as the air in the systemwould stop it returning to its original level.

Mark

[Guest]

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Hiya, I hope you're right, but the only pressure, would be above the water level, not below it, thus lettingthe levelreturn to normal.

What do our experts think ? Martin.

[nib]

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You could be right there Martin,ive got it fixed in my head that the coolant dont return to its normal position with a h/g weep but your right what you say about the rad being the highest point and exit point for air.

Mark

[GDPR]

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But lo! It came to pass that airlocks appeared in the high points of the cooling system.... and the Lord sent down a plague of head gaskets........

It sounds that you could have early signs of HGF, but it's worth a trip to your local friendly garage and have them run a chemical combustion gas detector on your cooling system. If the combustion gas check is OK, renew the pressure cap and thoroughly bleed the system for airlocks and try again.

Russ:dude:

[Guest]

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kryten wrote:

But lo! It came to pass that airlocks appeared in the high points of the cooling system.... and the Lord sent down a plague of head gaskets........

It sounds that you could have early signs of HGF, but it's worth a trip to your local friendly garage and have them run a chemical combustion gas detector on your cooling system.

Russ:dude:

When the head gasket on my old Polo gave up, our local guy was able to confirm with the emmissions probe in the air space above the coolant, nice to have the right kit. Martin.

[nib]

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Thanks Martin and Russ.

Where do they put the probe in the rad or expansion tank,but dont imerse the probe into the coolantand does the car need to be running?

Mark

[GDPR]

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I have a gas analyser in my garage, but not sure it's sensitive enough to detect a slight leak..... you would poke the probe into the airspace above the coolant - guaranteed to cattle the gas analyser if you dipped it in - it would need to be running.

The best way is with a "Head Chek" chemical tester - you suck the air from above the coolant through a chemical solution that changes colour in the presence of carbon monoxide

[nib]

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I will get it checked Russ.

Mark

[GDPR]

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Good man - catch it before it causes any damage

[Andy Rundell]

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This is what i have - not cheap, but considerably cheaper than gaas testing hardware:

http://www.frost.co.uk/item_Detail.a...0and%20Testing

......Andy

[Andrew S]

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That looks goof Andy. How much of the bottle do you have to use for each test? In other words, how many goescould you getif measured out?

I had an engineer use this on my BMW and it was fascinating. Fortunately for me it didn't change colour but he was adamant that it would if there was any doubt

Andrew

[Andy Rundell]

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Andrew S wrote:

That looks goof Andy. How much of the bottle do you have to use for each test? In other words, how many goescould you getif measured out?

i think there is enough for 8-10 tests in the initial kit, they do sell bottles of fluid on their own, not sure if they are the same size or not

[Andrew S]

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Thanks for that. It is a good kit

Cheers

Andrew