Lol. How is changing the thermostat going to fix the oil intermix problem you have in your coolant tank? Smoke coming out of your engine vent could mean some loose connections that lead to your coolant tank, among other things.
Two people on this board (one, a repair shop owner), have recommended you not drive the car anymore until you fix the oil intermix problem, but you ignore it and drive your car up to 75mph anyway. Lol. I think you should now drive it up to 100mph just for fun!