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Old 29-12-2012, 00:07   #1
bcoleman
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What makes coolant system pressurise

So I bought my ZS discovered a coolant leak then started to pressurise, had head off gasket had gone had that fixed but was still losing coolant couldn't see any leaks but now it is starting to pressurise again so far I've changed thermostat, water pump, radiator, 3x new caps, HG with a tested head and have tightened every jubilee clip I've even had the dash out to check my matrix I've checked all obvious places

So what else apart from HGF could cause the coolant to pressurise, it's not spurting out the top like before but if I do 8 miles and the car has been parked for over 24 hrs if I open the cap it hisses and the coolant rises
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Old 29-12-2012, 00:37   #2
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tbh 8 miles is enough to get a car almost fully (in terms of water temp anyway) up to temp so i wouldn't be slightly surprised to see pressure after a run of that length, my commute is 16 miles and blowers warm after 1-2, gauges at middle before ive got on the motorway.

Does it pressurise from cold? (i.e take cap off to release any pressure, put it back on, fire up from cold give it a few revs, is there pressure then etc)
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Old 29-12-2012, 00:39   #3
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You appear to have thoroughly checked and/or replaced all likely suspects.

Was the cylinder head to block interface checked for truth whilst the head was removed. This is how I check mine for truth using a quality straight edge and torch :~



I once had a 2 litre t-Series which had been poorly professionally repaired and skimmed. Still had pressure next day in cold engine like yours which it should not do. That skim was poorly executed and ahad a very slight bow and when the engine became warm, that allowed exhaust gases into the coolant passageways and not the other way when switched off. Pressure held fast as everything else was secure. In a healthy engine, pressure should decrease to normal after about twenty minutes depending on how warm the engine was in switch off.
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Old 29-12-2012, 06:37   #4
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have you asked Dave and keighleigh? it was them that did the hg..
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Old 29-12-2012, 07:04   #5
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I'd throw a can of K Seal in there and be done with it. Great stuff.
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Old 29-12-2012, 07:33   #6
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have you asked Dave and keighleigh? it was them that did the hg..
Yeah in talks with them about it, I'm just trying to find out if there's something else that could cause it as I know they did a good job and they are also being very helpful

Are they doing yours for you

I did try k seal at the beginning worked for a week then leak came back
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Old 29-12-2012, 12:01   #7
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Quote:
Originally Posted by Dr Dave View Post
I'd throw a can of K Seal in there and be done with it. Great stuff.
Lol..? Surely there should be a "lol" in there somewhere?!
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Old 29-12-2012, 15:48   #8
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have you checked the water pump for circulation i had one fail and it blew the safety on the filler cap and dumped the coolant the symptoms are similar to hgf
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Old 29-12-2012, 16:38   #9
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Quote:
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I'd throw a can of K Seal in there and be done with it. Great stuff.
You'll get shot you will!

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Lol..? Surely there should be a "lol" in there somewhere?!
, Im not sure if hes joking or not lol..
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Old 29-12-2012, 17:03   #10
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have you checked the water pump for circulation i had one fail and it blew the safety on the filler cap and dumped the coolant the symptoms are similar to hgf
Yeah it's deff circulating, just got me baffled
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Old 29-12-2012, 18:03   #11
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, Im not sure if hes joking or not lol..
I don't know either, i hope he is though!
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Old 30-12-2012, 09:40   #12
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I hope that was a joke because K seal is a joke... K seal will only work on hose or very minor rad leaks but wont cure any cyl head leaks its all crap and it turns your coolant into stew making it harder for water pump! keep away
I have done two HG's on the L series and both times had to remove alot of debris with wire wool and chemicals even got out the pan scrubber, many folk dont bother even pro's but I did and it worked fine.... so maybe a mucky surface causing it to not re sealed properly?? an internal leak on the cyl head should not be ruled out though, cracks, warping etc
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Old 30-12-2012, 10:28   #13
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So, in answer to the OP's question, it is the expansion of the coolant as it heats up that causes the system to pressurise. It is normal in a healthy engine. That additional pressure enables the coolant to operate at a much higher temperature without boiling than it would do at normal atmospheric pressure.

However, should there be a leak in the sealed cooling system, then it is not sealed. That means normal healthy operating pressure is never reached and that leads to premature boiling of the coolant.

Leaks come in many forms of course. Anything from a badly fitted coolant hose, a worn out radiator to a worn Water Pump allowing coolant to escape. A cracked or warped engine part allowing pressure to escape or compression gases from the cylinder to enter the coolant passageways will also cause coolant to boil over badly by overpressurising the system.

Two so called CHG 'failures' I investigated on "Spares or repairs" Rovers I've bought were as a direct result of incompetent repairs by professionals. One was a T-Series Turbocharged 600ti which had a poorly skimmed cylinder head ( close to 1000 Invoices for the work done ! ) allowing powerful compression gases into the coolant passageways once fully warmed up. The other a simple new exhaust manifold gasket incorrectly fitted on a K-Series which meant the Coolant "Elbow" could never seat properly on its own gasket allowing a steady loss of coolant once the engine warmed up.

Oh yes, worth mentioning two other so called pro repair "failures". One was a low mileage MG Montego Turbo which the previous owner had been charged 500 to replace the cylinder head gasket but it still boiled over once warmed up. Trapped between its Cylinder Head surface and Head Gasket was a small pea sized bit of dirt crushed near flat but allowing compression gases into the coolant!

The other a work colleague's one owner from new MG Montego 2.0 EFi which only needed a new Water Pump, not the 600 cylinder head gasket renewal he was quoted by a couple of repair shops. The water pump cost less than twenty quid and less than an hour to fit on the O-Series. Simple inexpensive repair.

I could mention other examples but the above will serve to alert folks that all too often the cars are wrongly blamed because as everyone knows following widespread and hugely negative media publicity....

THEY ALL DO THAT!

From the best evidence available to me, that of my own eyes and direct experience.... they do not all do that. The real failures lie elsewhere.
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Old 30-12-2012, 17:17   #14
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Cheers John I understand that bit though I don't think I worded my original post right what I really wanted to know is should there still be pressure in the system 24 hours after the car was last used and is HGF the only way it will over pressurise,

I have done the quick rev test and it does have pressure
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Old 30-12-2012, 17:24   #15
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Originally Posted by bcoleman View Post
Cheers John I understand that bit though I don't think I worded my original post right what I really wanted to know is should there still be pressure in the system 24 hours after the car was last used and is HGF the only way it will over pressurise,

I have done the quick rev test and it does have pressure
As previously explained, there should be no pressure left in the system the next day in a fully cooled engine. In a healthy engine, pressure should stabilise after engine switch off within an hour even on a hot day.

If there is still pressure in the system after a reasonable period, it looks like combustion gases are over pressurising the cooling system and not escaping the same way when engine is switched off. so, I would suspect a warped head allowing the gases to go the one way through the gap as it opens up as an engine gets warmer, then closes soon after switching off. This is in my very limited non-professional amateur experience with THREE Rover engines.

There is a slim chance that somehow with an Airlock somewhere in the cooling system, the over pressure remains for a much longer than normal time. Again in my experience, even that will settle to normal zero pressure well within an hour as the engine and system cools.

There again, could be something else well beyond the range of my experience.
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