Cleaning an old radiator

[Apu]

I bought an OEM replacement from Mania which has a thicker core than standard, great value and well...no worries!

[Steampunk]

There's not much wrong with using a second-hand radiator just as long as you feel comfortable with it and can spot tell-tale signs of misuse and wearing.

I bought a used one from a reputable guy/workshop whom I know won't sell anything he won't use himself.

[wiztek]

Damnit
Something is wrong. I think the loud bang might have been a head gasket blowing?
There is a lot of water coming out of the exhaust at the moment (definiately water, its clear) and this is in turn causing some white mist on revving (not smoke, and not in plumes), just a mist after hitting the throttle.
Also, theres a part of the exhaust that is now leaking (?!) - its towards the passenger side about halfway between the muffler and the engine (the cat?) and its a brown 'sweet smelling' liquid - smells like petrol.
All of this just cause i changed a radiator??!! what have i done...

[Steampunk]

the term "blown head gasket" does NOT refer to a sound, but more a colloquial term meaning the gasket is broken. It's like saying "burning" a DVD.

The water out the tailpipe is more likely condensation, not a problem at all.
the white mist is, again, evaporation of water/condensation in your exhaust.

...All of this just cause i changed a radiator??!! what have i done...

You're adding 2+2=7. The things you mentioned has nothing to do with the radiator.

[wiztek]

Yeah i know. The radiator was just changing two hoses. Should have nothing to do with these other issues im having.
I am going to put down the water to condensation. Its been pretty cold in sydney and this car hasnt seen the road for 2-3 weeks.

My main concern now is what seems to be petrol leaking...which would also go back to my initial issue of the backfiring/popping i had...

If it is fuel (its certainly smells like it) in the exhaust, i take it thats potentially very very dangerous.