My Nissan Micra is a 51 usually a good runner however today after work on my way down the main road which is 60 my car would not gain speed. It would only reach 40 at a push. When I’ve arrived to my destination it smelt. I lifted the bonnet and some smoke came out: not a lot, but enough to question. I’ve checked my oil and it was bone empty. I have topped it up and took it for a run and has picked speed up like normal. I only topped the oil up before Christmas. Is this normal or should I be worried?