I had something like this a while back, pressurising the coolant and that. I changed the hg, and found corrosion on the head on cylinder 4, allowing combustion gas to leak into the coolant galleries. I believe the total cost was £40 to have a spot of weld put on the corrosion, £35 +vat to have the head skimmed, £100 odd quid for a standard hg and associated gasket and valve stem seal set, and about a tenner for the head bolt driver.

If you've a haynes manual for reference, a clean working space, some mechanical experience, basic/essential tools and you're not a mug, you can get the job done for under 200 squids.

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Feelin so fly like a Gti6
Team >160,000mi

Take it to welshslug and have it done mate

/Thread

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"Supercharged - 454.1bhp/317.5lb/ft"
Peugeot 306 GTi-6
2000 (X), Moonstone