Exhaust has liquid after oil change

[chevybailout]

Everytime I get the oil changed when the engine is at operating temperature, the exhaust blows out plumes of water imediately afterwards. Also the engine idel is terrible along with acceleration for 10 -20 miles. If I change the oil when the engine is dead cold then these symptoms do not happen. The engine/radiator does not loose any fluid between oil changes. Any idea what is happening? Thanks,