My 98 chevy lumina LTZ 3.8L ,with 246000km,is smoking alot from the exhaust.The colour of the smoke looks normal,but a mechanic told me it smelled of oil not coolent. When i asked what it could be the cause.He said it would be costly to diagnose and repair. The smoke is more obvious when starting ,and especially when the engine had been running for a while and shut off, then started again.A big cloud of smoke is let out . But when driving away, and when idling at a stop the smoke is less odvious. I have'nt noticed any coolent loss, but have noticed oil loss at about a half quart to a quart every 2000 km. The car also has a problem with the Evap vent system. When the car is running the gas tank will collapse in ward with pressure ,and when i remove the gas cap the pressure is released. Can the Evap system cause the smoke from the exhaust? Or has any one else had a similar problems or any ideas of what can cause the smoke.