Hello i was driving my car the otherday and i started to hear a rattle noise then it was idling wierd then died? I stuggled to start it back up but eventualy it did. Poped open my hood and there was white smoke coming from the engine , opened my oil crank case and there was alot more coming out, temp reads regular, this started right after i switched my thermostat. Any help would be good!

Engine probably overheated. The stat you used may have been faulty, or all the air wasn't purged out of the cooling system. The temp sensor needs to be immersed in flowing coolant to properly read engine temp. A T'stat that is stuck closed or installed upside down will prevent coolant flow and the temp gage will report garbage. Air in system will cause a similar problem, and reduce the amount of coolant working in the engine.
The rattling noise could have been caused by preignition due to overheating, the oil pressure could have dropped enough, due to high temp, to allow the bearings to seize temporarily. In any event, smoke coming from inside the crankcase is usually a bad thing.

Dam well after i was done my stupid**s forgot to bleed the car and drove for about 30 sec then temp went slightly up but shut it down before anythng else happened

What is the best way to bleed system?

The way I do it is to open up the bleeder screws and the pressure cap, run the engine until the bleeders stop spitting out air and only coolant flows out. Then close the bleeders. Add coolant to fill point and repeat several times, tighten pressure cap. If the car has no bleeders add coolant to the fill mark, run engine till t'stat opens, Watch the temp gage, and keep the engine from overheating. When the t'stat opens coolant will flow in the reservoir and may try to bubble out as the air comes through. Turn off engine to let things settle, add coolant as needed and repeat. Eventually you will be able to run the engine with the pressure cap off without coolant blowing out in a geyser. There will be a certain amount of coolant expansion with the pressure cap off, but the coolant should overflow in gentle manner.

What do you mean pressure cap.?? I know were the bleeder screw is and the reservoir cap

I have a 1.8t btw sorry forgot to mention?

The pressure cap is the cap you remove to add coolant, either on the radiator itself or on the expansion tank, depending on the car.

was the smoke coming from the rear of the engine near the firewall>? I woudl check near the cat and if u see white crust on their its your coolant flange that it leaking.