I bought New Nissan 2 months ago. I was driving on down hills but as it was late at night and no car on the road, I enjoyed of high speed (4-5 min) and I didn't use the break . When we reached my husband was very angry and complained because he saw lots of smoke from my car while he was driving behind me. He said you damaged the engine because still car was cold (short drive). I would like to know in this case what happened to the engine and what was the reason for the smoke? and really is too bad for engine if I don't use break in down hills (I always thought is better for engine)? Also he said new car you shouldn't go high speed at least for 5-6 months. Is that right?
If you didn't come close to redlining the tac (high RPM) and it doesn't smoke now, you are probably ok. Engines are not what they use to be, they last a lot longer and are made of improved materials. Break-in time isn't a critical as it once was.