help! I've broken something changing O2 sensors
 

After reinstalling everything and starting the car, white smoke began billowing from my engine bay. I refurbished all of the O2 sensors and it went away for a short period and now is back. Did I break my catalytic converter lowering it a few inches? I've gotten under there and tried to shake it to find any broken sections but can't seem to find any. No warning lights.

Muffler shop says that it is not the Cat. Any guesses?

I believe that white smoke is from a coolant leak.

Thanks! The overflow tank does look low. I'll start checking hoses.