This my 04 A4. I noticed the telltale white smoke from the exhaust first off. After investigation I noticed that when I pulled the plug on #3 cylinder it was wet, like coolant wet. Figuring it was a head gasket I pulled the head. I carefully examined the head for signs that the head gasket had failed but I saw a nice crisp line where the head gasket had sealed on not just #3 but on all the cylinders on both the head and block. I closely examined the head with a magnifying glass for cracks but found none, same with the block. I also checked the head and block surface for flatness. One thing I did notice was there was a vertical line running the full length of #3 that appeared almost like a stain from the top of the cylinder down the length of it. I could not find any crack associated with this line. I'm thinking it might have been coolant leaking down the cylinder wall when the car is sitting causing this stain. Anyway after reassembling the head with a new gasket the problem persists, coolant is still getting into #3 cylinder and white smoke is coming from the exhaust. Where do I go from here? I'm thinking a leak down test, which I should have done in the first place. Next how obvious should a crack in the head or block be? I've seen cracked 2 stroke cylinders before and they were obvious. Any suggestions?

 

I'd have the head checked for cracks. That's the most obvious place. Sometimes it takes using the special dye applied to the head to reveal the crack that might not be visible to the naked eye.