1996 VW Passat--Head Gasket issues

I have a 1996 VW Passat GLS(gas, 4 cyl. 2.0, 72K miles, auto trans) that just had the head gasket replaced. It seemed to hold just fine, however after about 30 minutes of running (idle) it started to show signs of combustion gasses in the coolant.(Did a coolant gas test) We then put the "magical" water glass in it and retested after following the directions. NO GASES in the coolant!
However, it still seems to have a lot of white smoke coming out of the tail pipe. Could that be due to the catalytic converter being full of coolant residue? Also the top radiator hose gets warm, but the bottom one stays pretty cool, not even warm. Circulation problem? The car was ran for quite a while I think after the gasket blew. (Auction car--so am not real sure) My mechanic is not real sure of the problem. So thought I would ask here. Thank you for the help!