Several points to cover: first off, when I worked for a major U.S. auto manufacturer, we had customers who were told very specifically that their warranty would be voided if they made certain performance modifications. These people made the modifications, had problems, and we fixed them every time with no questions asked. The manufacturer's position was that not fixing the cars created bad publicity, no matter if the owner did install unacceptable equipment. In 15 years I never knew of anyone having a warranty voided for any reason. With domestic car makers, it just doesn't happen. I don't know about imports because I never worked for an import company. I hear that Hyundai does because of their 10 year warranty, but I have no direct knowledge of that.
And I'm not in favor of lifting off the gas while the tires are spinning, but I can't imagine why anyone would. Even if they did, the momentary stress would be less than just accelerating quickly. Also, the same principle of lower friction applies to sliding turns using the emergency brake. Because the tires are sliding, they are exerting less force on the road and causing less suspension stress than just hard cornering.
It is a given that modern cars will at some point be faced with situations that require acceleration (such as passing on two-lane roads or merging into fast moving freeway traffic). It is also a given that at some point braking and sudden turns will be required, such as avoiding accidents due to careless drivers. Car manufacturers could never dream of 100,000 mile warranties if cars were as fragile as some people seem to think. Flat out acceleration, panic braking and hard cornering are considered a necessary part of a car's life by the engineers who design them. All cars are very much over-engineered to accommodate these real-life possibilities.
As for as break-ins are concerned, modern cars don't require any. Engines are pre-run before the cars are ever delivered to dealers. Close tolerances on modern engines negates any need for granny-style driving after purchase. The one thing most car experts DO agree on is that new cars should be driven at varying speeds and accelerated very hard for the first few hundred miles. The line about full-throttle acceleration being beneficial comes from a Chrysler owner's manual. My Dodge truck manual carried that recommendation, and to my knowledge all recent Chrysler owners manuals do. Ford owners manuals don't say anything about break in periods at all, and I don't know about GM.
I didn't say lifting off the gas was a good thing. I mean if theoretically all force from the drivetrain was terminated, then the tyre will stop spinning almost instantly, indicating the amount of force required by the engine/drivetrain to keep the tyre spinning. It is still not a good thing to do, just adding more wear and tear.
Oh, and do they really run engines now before they're up for sale? Seems like a time consuming process, but will result in a much better product, seeing as the engine is being "run-in" properly.
And of course flat out acceleration is fine, but the car MUST BE WARMED UP PROPERLY. Cars aren't designed to be run hard with low oil pressure, or improper lubrication (cold oil). Synthetic oils reduce the harm, but it still adds months, years of wear driving a cold engine hard.
There is a lot of very contradictory (and highly questionable) advice from so-called "experts" regarding breaking in new car engines. One source recommended changing the oil at TWENTY MILES!! Lots of luck on even finding a new car with that few miles. Test drives will generally add that many miles easily. Most of my new cars have had at least 100 miles on the odometer. One of my strongest rules regarding cars has always been LISTEN TO THE MANUFACTURER. They build the cars. They know what is best.
When I bought my last new Mustang, I wanted to change to full synthetic oil as soon as possible. I asked the service manager at the dealership where I bought my car if I could change the oil at only 2000 miles (7000 is the recommended change interval). He replied "ABSOLUTELY NOT!". He said it was very important to leave the original oil in for no less than 5000 miles, so I did as he instructed.
Sources recommend ridiculous things that are totally at odds with the manufacturers recommendations. I see recommendations to change transmission fluid at 10,000 miles. No manufacturer recommends that. The owner's manual in my last GM car said "under normal driving conditions the transmission fluid NEVER NEEDS CHANGING". I heeded that advice. In fact I have never changed transmission fluid in any vehicle I have ever owned, and have never had a seconds trouble with any of them.
I see comments stating that owners change oil at 3000 mile intervals. That is fully twice as often (or sooner) than most car makers recommend. Modern cars using full synthetic can easily go 10,000 to 15,000 between changes. I generally change at 10,000 mile intervals, but I have a friend who changes oil in his Cadillac at 25,000 mile intervals. He has never had any engine problems. Synthetic oil does not degrade.
Somehow I feel that driving conservatively is going to make my vehicles last much longer. Running high RPM, speed shifting, hard cornering, frame cracks from jumping and braking is accelerating component wear. New or old, the same result. I may be alone in this, but I feel long term it's going to pay dividends on the drivetrain and suspension deterioration and heat buildup.
I am not buying rental cars. I suspect out of a thousand plus renters, there will be a few that really get their moneys worth when returning them. Knowing my luck, I would get a car that was renting out for one of recent Jackass 1 or 2 movies.
There is no question that increased stresses on a vehicle due to red-lining the engine, very hard cornering and repeated hard braking may have an adverse effect on the longevity of a vehicle. To argue otherwise would be in defiance of the laws of physics.
Just how much effect such behavior has on a car is the big question. I am a very aggressive driver and very often push my small-engined car to red line while passing or merging. I do not slow to a crawl over speed bumps and often take corners at the posted speed limits rather than slowing down. If such behavior has had any effect on my cars, it has been too little to notice. I generally get well over 100,000 miles out of all my vehicles with zero repairs. I have never had an alignment or replaced shocks on any car I have ever owned. I virtually never replace brake pads before 100,000 miles.
As a general rule I trade my cars at around 100,000 miles now, because I simply get tired of them. I have, however, kept a few that we were especially pleased with until well over 200,000 miles. We had no problems with any of those either.
I have always broken in every new car I've had (and most of my cars are bought new) flat out from day one with the exception of my very first new car (a Plymouth). I broke that car in in the "old lady" fashion that many people recommended. It, too, proved totally reliable until I sold it at 160,000 miles. It did, however, use oil from the very first.
From my own experience I don't feel that aggressive driving makes any really noticeable difference in a car. Perhaps if you keep a car over 300,000 miles the difference might become more apparent, but very few people keep cars for that length of time. My brother, who was also a spirited driver, did start having a few minor problems with his Ford after 320,000 miles.
I have no qualms at all about buying a car that has been driven hard. I especially prefer used rental cars because you can be assured that they have been properly maintained, and the interiors are always kept flawlessly clean.
I saw on the news that many new rental cars were not taken in on recalls. Just re rented. I suspect due to the downtime doing so and the volume involved. That may have been addressed however.
I totally agree with this comment. I rented a 2012 Nissan Versa. I was completely surprised by the low quality of the car and the very bad MPG! The car had a very hard time going to 70MPH. Talking MPG, the car was hardly making 23 MPG. I was really surprised. It had 8200 miles only!!
Later, I had the opportunity to drive a friend's Versa, with 24K miles. That car was amazing! According to him, he is averaging 30 MPG. That the second Versa has a CVT transmission.
A rental is not a way to judge a car or maker...