2.1DJ - Fault finding coolant pressurisation (yes I know...)

[ManicGTI]

Firstly - apologies for the millionth coolant question, I know it's a well trodden path but i'm banging my head try to solve it and getting nowhere.  After a trip to France a few months ago we were losing a lot of coolant, filling up the top up tank etc and only got home by refilling constantly.

- I assumed that I had bled incorrectly and had leaks, so I dumped the coolant and ran it locally for a few weeks on plain water with UV die.  This highlighted a number of small leaks from rubber hoses so decided to go over everything replacing anything looking suspicious.

- Fitted NEW Stat (80deg) and stat cover housing, all coolant hoses in engine bay (inc the small hardlines and larger hoses to the plastic hardlines), expansion tank, Blau darlek Cap (I have 3 of these now, all quack fine), all oil/coolant temp senders, rad fan switch.
- Flushed with hose and lower return line disconnected.
- Refilled and rebled with libby bong, Pink G12 and heater on hot.
- Ran up to temp at idle, checking stat opens with IR temp gun (return line gets hot) and rad fan kicks in at the two temp levels as expected.
- No visible smoke from exhaust at idle, Water jackets look like they have been changed at some point, no obvious external leaks.

I've been driving around doing short journeys with with no issues.  But before a big trip up north I did a slightly longer test drive (1hr each way) down to Just Kampers to pick up rad hoses and stainless coolant pipes and stress test it a bit at higher speeds.  I stopped a few times along the way expecting to find 'some' air  in the rad, but it was awful, nearly every time I stopped there appeared to be loads of air in the rad.  Got to JK and let it completely cool down, popped the libby bong on again, refilled/bled.  On the way back temps started to head upwards pretty quickly, flashing light came on (coolant level), heater blowing cold and hot intermittently, top up tank FULL to the brim and overflowing with coolant.  This is all the same symptoms I was having in France so clearly I have solved nothing.

So I guess i'm here to see if there's something obvious i've missed, and see what thoughts people may have on causes and next steps?
- i'm happy stat and tank cap are behaviing correctly, and there's no visible 'bulk' leaks of coolant externally.  Unchanged are: rad, rad hoses, long hard pipes, heater hoses/matrix, water pump.

- Could this just be from poor bleeding technique?
- Head gasket / head leaking at higher temps? 
- Heater matrix leak?  (how can I check this?)

Suggested next steps?
- Refill and rebleed....again?
- Compression Test 
- Coolant Sniff test?  (Are the home kits any good or worth taking to a garage?)

Thank you and apologies for what is clearly a pretty common problem being posted again.  This issue has basically meant we have to resort to sqeezing (3 kids young kids) into our Golf for trips this summer until I can trust it to some degree, pretty disappointing.

[Stesaw]

If the topup tank is getting coolant pushed into it til it over flows out the breather then as I understand it there is only one thing that can cause that and it's exhaust gasses getting into the cooling system from the engine, so perhaps an internal seal on one or more of the barrels isn't doing its job on the engine. You can also get a hole in the head which cause gas from combustion to get into the coolant system and pressurize it. I think Mocki has had that happen to him on an engine if I recall.

You might be looking at a top end rebuild on the engine, I could be overthinking it but I am sure others may have some ideas as well.


 

[Aidan]

it sounds like products of combustion in coolant, a sniff test will confirm
 

[ajsimmo]

Fire ring seal breached. Definitely, no question. (Unless - very unlikely - cracked head).
Only fix is remove heads and replace fire rings.

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[ManicGTI]

Thanks for the replies guys, i'll order a sniff test kit online as the first port of call.

Is a leak down test worth it to try and identify which cylinder?

[Stesaw]

Might be an idea, save you dropping both heads.. but I suppose if the valves are tired you might get a loss either way

[ajsimmo]

Is a leak down test worth it to try and identify which cylinder?

It almost certainly won't leak under such low pressure, and the test will not find the fault. It's usually only during combustion stroke at revs/under load when pressures are at max that it'll force gases into the coolant.


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[Stesaw]

Is a leak down test worth it to try and identify which cylinder?

It almost certainly won't leak under such low pressure, and the test will not find the fault. It's usually only during combustion stroke at revs/under load when pressures are at max that it'll force gases into the coolant.


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It should find issues with valves sitting right though?, I know thats not the issue that manic has but may be worth looking at if he doesn't know the condition of them?  

[ajsimmo]

Ok, I suppose there may be lots of things on his van that are worth looking at, but the question was about coolant pressurisation. Whilst trying to diagnose it's easy to get sidetracked. However, the heads need to come off anyway so why not pop the valves out and lap them in whilst the opportunity is there.

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[Stesaw]

Ok, I suppose there may be lots of things on his van that are worth looking at, but the question was about coolant pressurisation. Whilst trying to diagnose it's easy to get sidetracked. However, the heads need to come off anyway so why not pop the valves out and lap them in whilst the opportunity is there.

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Yeah its easy to sidetrack from what OP was asking when it comes round to it. I wasn't belittling you're knowledge incase you thought that.

[ajsimmo]

Ok, I suppose there may be lots of things on his van that are worth looking at, but the question was about coolant pressurisation. Whilst trying to diagnose it's easy to get sidetracked. However, the heads need to come off anyway so why not pop the valves out and lap them in whilst the opportunity is there.

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Yeah its easy to sidetrack from what OP was asking when it comes round to it. I wasn't belittling you're knowledge incase you thought that.

Not at all, I just see a lot of threads go off at a tangent which can muddy the waters somewhat. Just tugging on the reins to keep on track

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[ManicGTI]

I didn't realise I hadn't responded to your replies, thanks all for replies.  All kind of confirmed what I already suspected to be honest...

The engine looks like it's been apart previously (water jackets look in great condition externally), so my current plan is to pull the heads, give everything a clean / inspection and go from there.  If no major issues then pop in new gaskets and get it back together.  I'm lacking space at the moment so may have to do with engine in, but will cross that bridge when I get to it.

The two main possible sticking points seem to be condition of studs, and avoiding pulling the liners out with the heads if possible.  Given I already know I have some sort of issue, if something goes wrong and the engine needs to come out, so be it - I'll re-evaluate.