[Efthreeoh]

So when the car is smoking from the exhaust get out and put you hand right in front of the exhaust outlets and let the exhaust condensate onto your hand. Then step away from the car and smell the condensate and see if it smells sweet like coolant. If it doesn't then you have a coolant leak which you are smelling and attributing to the exhaust smoke. Id' say you have a coolant leak somewhere because adding that much coolant in that short of a period is a bit excessive.

A headgasket leak should show up in the oil as milky-white thick residue on the underside of the oil fill cap. The early N52s were known to break head bolts both outside the head near the oil filter housing and inside the valve cover at the front of the head. Check if the head bolt is broken near the oil filter housing. The head of the bolt will either be missing or will lift out of the hole. Have compression test done to check for a headgasket leak if you can't find the coolant leak.