1992 Mitsubishi 3000GT White Smoke

It has 200,000 miles on it. The owner before me said that the engine was rebuilt about 20,000 miles before I got it and I have only put on about 10-12,000 miles. The car is blowing white smoke out the back end when accelerating. Not sure if its head gasket or the turbo. Good news, the temp stays cool. No bubbling of the coolant, so I am thinking that it is actually the turbo. Other cars I have seen have jumped in temp with a blown head gasket. The front three cylinders, the plugs look good, no coolant.