I read several older epic threads about coolant smell. It took me days to read, inlcuding "summary of problems" but it is possible that I missed to read some newer updates. My case, 2013 1.4T, about 60k miles:
Smells outside and inside.
Dealer recently replaced the water pump finding a leak, which did not help, actually seemed to make worse in terms of smell (I did not complain about smell at that time, they replaced it under power train warranty after I reported what appeared to be an oil leak from the car, at which time they also replaced oil pan seal).
Tried new o-rings on the cap/relief valve including thicker one. Minimal improvements.
Tried another surge tank cap/valve (borrowed one from a friend Malibu, same 140PSI spec), no change.
There are no visible coolant leaks that I could see. Coolant level remains steady, or vanishes at a negligible rate.
I improvised that "diversion" system, put a hose on the coolant surge tank vent to bring vapors outside engine compartment (house sticks outside around drivers side headlight). This seemed to reduce smell inside, but makes it worse outside - the whole garage is now filled with smell when I park.
Where do I go from here? Should I possibly try new surge tank? I'm reluctant to go to the dealer as it does not look this issue is covered by power train warranty or a recall, so just to "diagnose" will be $100, with slim chances they will nail it down.