One extra quart of oil isn't going to hurt. Neither is neglecting a scheduled oil change. It sounds like the cylinder head gasket is leaking or the head is cracked. Coolant leaking into the combustion chamber through a leaking head gasket or cracked head causes white smoke from the tail pipe. Your mechanic can do a chemical test at the radiator to verify a leaking head gasket.
There is nothing you can do to cause a leaking head gasket, other than possibly overheating the engine, but failing to replace the engine coolant every two years might make the problem show up a little sooner. Acids normally form in the coolant and the corrosion inhibitor and water pump lubricant additives wear out in about two years. That's when those acids start to work on metal parts including the head gasket.
If you still have the red Dex-Cool, ("Dex-Mud") antifreeze in the system, GM advertised that as "lifetime" coolant to make the cost of maintenance appear lower than their competitors. Hidden on the reservoir they snuck in the three-year replacement recommendation. Even that is too long.
Tuesday, April 30th, 2013 AT 3:01 PM