You did not mention what kind of car it is. However, what kind of smoke ? If it is blue(oil), it could be that the car is one with fairly "low tension" piston rings, which can quickly become ruined in a situation of severe overheating.
If it is white smoke, you still have an internal coolant leak of some kind that is causing anti-freeze to enter the combustion chambers.
prolly a blown headgasket or results of a preexhisting headgasket problem. if your headgasket isn't blown or you fixed it before drain the contents and add more oil.
I just replaced mine, came to $1080 before taxes.
Any exhaust smell in a car cab indicates an exhaust leak somewhere along the line. Th reason you don't smell it while driving is because the air flowing air under the car is blowing the exhaust gasses away before it can rise into the cab. After the car sits for a while, the gasses seep out of the leak, and up into the cab.
Take it back immediately to who ever did the exhaust work.
The exhaust pipe will need to be replaced, or, you can buy a quick-fix patch at your local auto parts store as a temporary fix. It's a treated "ribbon" about 2 or 3 inches wide that you can wrap around the exhaust pipe to cover the hole. The heat of the exhaust activates the chemicals in the "ribbon" to make it adherent. I believe the product is called a muffler repair kit.
It is screwed into the exhaust pipe just before the catalytic converter.It is screwed into the exhaust pipe just before the catalytic converter.
Make sure your just not losing water that was in the exhaust before you replaced the head gasket.
It is right below the exhaust manifold before the down turn of the exhaust pipe and before the catalytic converter.
It helps clean up the emissions from the exhaust system before they are released into the atmosphere.
It's possible that it's the thermostat or a blocked radiator, but if it's blowing the coolant before the engine gets hot it could be the headgasket. BMW's are notorious for having a problem with warping heads easily if the engines overheat.
Low coolant, stuck thermostat, blown headgasket (from overheating BEFORE) or a damaged (rusted) water pump.
White exhaust smoke almost always indicates a head gasket, or possibly, intake gasket leak. Often, the exhaust will also have the odor of antifreeze. The white smoke is actually the water vapour caused by coolant entering the engine's combustion chambers. This requires immediate repair before further damage is caused to the engine.