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[tunnie]

Pressure tester in Brackley, not had chance yet.

Well, not worth writing off the car if its a £2 seal

Which £2 seal? 

[TheBoy]

Pressure tester in Brackley, not had chance yet.

Well, not worth writing off the car if its a £2 seal

Which £2 seal? 

The one its leaking from.

[tunnie]

That does not help as I don’t know where it’s leaking 

[TheBoy]

That does not help as I don’t know where it’s leaking 

You probably will when you pressure test it with all the plenum off and inlets out

[henryd]

Certainly the misfire at cold start with coolant loss is indicitive of water getting in the cylinder/s

[tunnie]

That does not help as I don’t know where it’s leaking 

You probably will when you pressure test it with all the plenum off and inlets out

I think I need a visit to Brackley and a curry to confirm this 

[tunnie]

Certainly the misfire at cold start with coolant loss is indicitive of water getting in the cylinder/s

Yes. 

[TheBoy]

Certainly the misfire at cold start with coolant loss is indicitive of water getting in the cylinder/s

Surely that would lead to excessive pressure in coolant system, seeing as cylinder pressure are way more than coolant pressure.

[henryd]

Certainly the misfire at cold start with coolant loss is indicitive of water getting in the cylinder/s

Surely that would lead to excessive pressure in coolant system, seeing as cylinder pressure are way more than coolant pressure.

Which would explain leakage at cap if its venting constantly

[TheBoy]

Certainly the misfire at cold start with coolant loss is indicitive of water getting in the cylinder/s

Surely that would lead to excessive pressure in coolant system, seeing as cylinder pressure are way more than coolant pressure.

Which would explain leakage at cap if its venting constantly

That thought had crossed my mind, but had credited the useless student with a bit more noggin....

[dave the builder]

Certainly the misfire at cold start with coolant loss is indicitive of water getting in the cylinder/s

Surely that would lead to excessive pressure in coolant system, seeing as cylinder pressure are way more than coolant pressure.

4 stroke engine
suck -cylinder pressure negative  sucks coolant too
squash
bang
blow

[TheBoy]

Certainly the misfire at cold start with coolant loss is indicitive of water getting in the cylinder/s

Surely that would lead to excessive pressure in coolant system, seeing as cylinder pressure are way more than coolant pressure.

4 stroke engine
suck -cylinder pressure negative  sucks coolant too
squash
bang
blow

With the squeeze and subsequent bang resulting in proper pressure

[dave the builder]

Certainly the misfire at cold start with coolant loss is indicitive of water getting in the cylinder/s

Surely that would lead to excessive pressure in coolant system, seeing as cylinder pressure are way more than coolant pressure.

4 stroke engine
suck -cylinder pressure negative  sucks coolant too
squash
bang
blow

With the squeeze and subsequent bang resulting in proper pressure

yep, but the coolant droplets won't go back to the coolant through the fail, but gas pressure will ,but Tunnie may not be seeing it .

sniff test or remove all the plugs and pressure test over a long period to see if coolant leaks into cylinder

also worth cracking open the oil sump plug, to check that coolant is not leaking into cylinders over night, then settling in the sump .(water sinks to the bottom ,so you don't need to drain the oil)

[tunnie]

To answer a few questions:

- Coolant pressure is good, I think the leaking cap was eBay crap replacement
- Release new GM and cap, no more than usual hiss after 50 miles.
- There is a whiff of petrol in coolant, at least to my nose.
- Better sealed coolant tank, has seen increase in coolant use
- new tank also sees more of a missfire when cold

That all said, exhaust gas looks fine. Even on cold start, no signs of steam.

[dave the builder]

sniff test like this clicky
though it does sound like a tiny leak , but proper testing (sniff and long term pressure test) would prove ,one way or another .
had it been a simpler engine ,I'd have said wondaweld , but bypassing the matrix, oil cooler ,rad and stat would involve nearly as much work as whipping the one head off on a V6