I've got an s4 that I bought, but when I went to drive it that first day and it got all the way up to temperature, all the coolant (water, thanks to the previous owner) started boiling and pissing out of the overflow reservoir. Hoping that it wasn't bad coolant seals, I began trying to get any air out of the radiator (knowing that having air bubbles in there can cause the same thing), so I got one of those cool funnels, and I tried bleeding the air from the system, but there was just constant bubbles (sounds like exhaust gasses due to bad coolant seals), but here's my question: it puts out almost no smoke when it runs, only a little when it starts cold, then when it warms up none at all, and I know that thick clouds of white smoke is an indicator of bad coolant seals, so is it possible to have bad coolant seals and have the exhaust gasses pressurizing the system, but NOT have smoke?

 

Is your over flow tank empty? After you drive can you smell coolant?

Check with your favorite auto parts store to see of they do tool rentals and borrow a coolant system pressure tester. Put the system under pressure and see if it holds. If you lose pressure then you know for sure you've got a leak somewhere