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Old 23-05-2011, 17:25   #1
stevelift
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Should I have constant pressure in coolant?

Hi, I am new here and in need of some advice if anyone can help.

The HG went on my 75 1.8 and I replaced it with the multi layer gasket. I have now noticed that the cooling system is under constant pressure, even when it has cooled down. If I take the expansion cap off and release the pressure, after a short run at normal temp. the top hose is under pressure, as I would expect when hot. But when the engine is cold the pressure is still there, even if the car is not used for a few days it remains under pressure. It does not appear to be losing water (some forces its way out when i remove the cap, when cold.

I have not had this car long and have not had a K series engine before so I don't know if this is normal or if, as I suspect, combustion gasses are getting into the coolant. There are no signs of oil in the water or vice versa since the HG was replaced.

Any help/advice on this would be greatly appreciated.

Steve.
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Old 23-05-2011, 20:08   #2
Mr Edd
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My first advise would be to replace the expansion tank cap. About 12 off eBay. There are specific pressures for the engine but I can't remember what they are.

I think they are known to loose their properties especially after a heating problem.

Edd
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Old 23-05-2011, 20:15   #3
iggie
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I stand to be corrected, but my impression is that the coolant should only be under pressure as a result of expansion of the coolant liquid due to heat; therefore when the engine is cold, so will the coolant be, and no residual pressure should remain in the system.

Filler caps are known to be suspect, but unlikely to be at issue here.

As to where the pressure is coming (& staying from), others more knowledgeable of the 1.8L will be here shortly!

HTH
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Old 23-05-2011, 20:20   #4
1955diesel
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The system should only be under pressure when hot.

Pressure remaining when the engine has cooled down of course makes me think of gas leaking past the gasket, but if this was the case I would expect you to have air lock problems - no heater and engine overheating.
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Old 24-05-2011, 07:57   #5
jcwatrichmond
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If you did the HGF job yourself, or if a garage did it, how confident are you that the correct proceedure was followed? It's quite a technically advanced and carefully stressed cylinder head. The liners must protrude a fixed amount above the block and the bolt tightening routine is critical.

JCW
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Old 25-05-2011, 08:03   #6
Mike Noc
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Quote:
Originally Posted by jcwatrichmond View Post
If you did the HGF job yourself, or if a garage did it, how confident are you that the correct proceedure was followed? It's quite a technically advanced and carefully stressed cylinder head. The liners must protrude a fixed amount above the block and the bolt tightening routine is critical.

JCW
Also finding out what caused the failure in the first place. Last one I saw had a slight weep from the underside of the top hose when under pressure.

Mike
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Old 25-05-2011, 09:18   #7
Furryroo
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Even when cold, my 1.8K series still has preassure in the expantion tank (hisses when you take the cap off) it has never had a head gasket replacement, does not lose any coolant or have any mayo in the oil / oil in the coolant

As far as i was aware, this slight pressure remaining is normal
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Old 25-05-2011, 10:05   #8
T-Cut
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Pressure in the cooling system is caused by three things. Thermal expansion of the fluid means the air in the expansion tank gets compressed, Temperature rise of the coolant also leads to an increase in vapour pressure. Entry of permanent gases from the exhaust, either via HGF or a liner issue. The first two causes reverse as the engine cools. The third remains as pressure in the cold system.

TC
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Old 25-05-2011, 13:53   #9
1955diesel
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It could probably also happen if corrosion was taking place due to old antifreeze.
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Old 25-05-2011, 14:36   #10
rolled1
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I had pressure remaining in the system of my last car (a ford) even when cold,the heaters would blow cold as well,the problem was a cracked head leading to the car being wrote off as the cost of repair was excess of 5000 and car was worth 9k,luckily for me the car was replaced under warranty
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Old 25-05-2011, 14:43   #11
T-Cut
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If the coolant pH dropped below 3 or so, or rose above 12, aluminium alloys would generate hydrogen. It would be a considerable explosion hazard. I'm not sure how those changes might happen though.

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