I was drivin in the cold one mornin, car only just reached warm position, and noticed a bit of steam come out from grill and something smelt REALLY horrid. Checked hoses and coolant and for dead animals (lol) or something that could cause it, but nothing found. Car's running fine, and have driven a bit since, but today I checked my oil filler cap, and it's very slightly milky colour in the top of the cap.

Questions.
1. Would this usually indicate head gasket blown?
2. Is it a bad idea to keep driving the car for a few days if it has blown? The car runs fine, I havent checked to see if it blows white smoke or anything. And the weird smell is disappearing