2008 BMW 318i smoking

White smoke is normally a sign of burning engine coolant due to a leaking cylinder head gasket, but lack of lubrication would also cause internal parts to get too hot and a cylinder head could be cracked. To verify coolant is getting into the exhaust system, you can add a small bottle of dark purple dye to the coolant, run the engine long enough for it to circulate, then search with a black light. The dye will show up as a bright yellow stain that you can follow back to the source. If you see the dye inside the tail pipe, the cylinder head will need to be removed for inspection.