I have the white smoke in the mornings here in the ACT and all it is is the condensation hitting the cold air. The other thing that happens is when you shut off the vehicle, the water condensates and sits in the low points in the exhaust and pools. The rear muffler is the worst place for it hence why they rot big time. I too replaced the O2 sensors in my XR8 and my economy was perfect again...600km a tank of 95RON and 400-450km of LPG.

I saw an I6 Fairmont up the street blowing white smoke however this was lingering white smoke - a huge difference - and found out she had chewed a valve and was dispensing oil directly into the exhaust manifold...was like an oily fog drifting down the street...

Sorry for the waffle

Fuel = black smoke
Oil = white/blue smoke
Water = steam