Originally Posted by randomae
Some people think you should push your car really hard initially to seal the rings. Some say you should treat it delicately and vary the RPM ranges. Some say all the breaking isn't necessary because the factory machined clearances are so close compared to cars even 10, 15 years ago.
After a ton of research I don't believe anyone knows for sure what to do when you first get a car.
Yeah, do what feels right. I usually drive like a normal person (don't baby it, but don't go WOT either) for the first 200-300 miles, then get a bit more aggressive for the next couple hundred and then try not to think about it.
Then my dad says break it in the way you plan on driving it, that it's bad to baby the car for the first few weeks if you are going to be aggressive with it later. Basically it's like asking an athlete to sprint without training--good recipe for a pulled hammy. It's also a good reason why you let your car warm up in the morning, but do so by driving it gently--not by letting it idle in your driveway for 15 minutes.
Also, being an engineer myself, you wouldn't leave something that critical to the performance of your product in the hands of the consumer. If engines really needed to be broken in for 1000 miles before the were ready for prime time, then it would be done at the factory. Imagine if you bought your AMOLED phone and you were told to leave it on an all-white screen for the first 100 hours (which is more or less what's done at the fab before shipping them out).
Last thing, I've purchased 3 new cars and have never had a dealer say a word to me about a break in period.