On my high performance cars I break them in on the dyno after an oil change. I always change the oil within 300 miles.

While several of my GM friends have oil consumption issues I don't lose a drop after 5000 miles.

 

From what I have read most motorcycle and aircraft engine builders agree on seating piston rings in the first few hours or losing the opportunity to have a good seal. It probably is better to have at least a few good power runs during break-in than to barely run above idle. Between dealer prep and the first drive most cars are doing just that - idling. The problem with hard running is that the piston ring contact can easily overheat and glaze when barely seated. Once glazed the surfaces will not form a good seal. Yes the engine should be warmed up but to overheat is just as bad. I followed a middle of the road break-in for my MINI starting at 4 miles and was especially careful not to get the engine too hot or exceed 4500 rpm the first 150 miles. It was harder to keep my foot off the pedal than to push it but I did avoid WOT.

We have a Mazda 3 that I broke in very hard from day one and it was using oil for the first 5,000 miles. I thought it was a mistake, but now at 15,000 miles it uses little or no oil. I have never seen an engine use less oil so late in the game.

I would not use an extreme method to break-in but some degree of pushing the engines is needed to seat the rings. Here is one article I think explains the process very well. It emphasizes that lugging is worse than high RPMs, but I wouldn't go hitting high 5K with abandon:


http://www.ntnoa.org/enginebreakin.htm

 

Let me throw something else in the mix.

Everyone seems to be focused on the engine break-in-seating rings, wearing in cylinder walls, etc

What about the rest of the car? I have been around for a long time (driving now 44 years) and have had over 30 cars, new old and inbetween.

With a new car, not only is the engine in need of break in but the car needs brakes to wear a bit for 100% function, the transmission also wears in and even the tires do't have full stopping power til they are a few months old.

Now I know the comments about the MINI being run before it leaves the line, but the car is not driven and the clutch, brakes, etc are not broken in. the clutch needs to have a carbonized layer built up or the surface glazes and does not funtion properly.

If you break in the car hard, as has been suggested what about the rest of the car? Will you shorten clutch life? Brakes? Transmission?

The BMW autos are arguably one of the best fitted and engineered cars and this is what a tech bulletin reads:


BMW AG - TIS
RA: Breaking in SAC clutch
Issue status (03/2002)

Break in the friction linings of the clutch by applying light to medium loads, in the same way as for brake linings. This preconditioning creates a carbon layer between lining and metal friction surface which in the end generates the necessary coefficient of friction. Breaking in can take the form of either normal driving with many gearshifts or a specific breaking-in program on gentle gradients.

"Normal" driving will not damage the clutch. "Normal" driving conditions involve drive-off speeds of up to approx. 2500 rpm on a medium gradient, e.g. when driving onto a transporter. Normal driving off on a level surface at speeds up to approx. 2000 rpm are likewise sufficient.

Sporting driving maneuvers will destroy a new clutch! These include driving maneuvers at high differential speeds, overlaps or very high drive-off speeds, e.g. when driving onto a transporter.

When a vehicle is moved "normally", an empirically established figure of approx. 800-1000 gearshifts is applicable to an optimally broken-in lining.

Please conduct the following breaking-in program in order to avoid later customer complaints:

* specifically for M5 and Z8 vehicles

Breaking-in program for approx. 30 km on road

Vehicle subject to "moderate" shifting processes

Drive off at max. 2000 rpm; upshift 1->2, 2->3, 3->4; upshift at 3500-4000 rpm, downshift 4->3, 3->2, 2->1, downshift at 2000 rpm

Drive off 3 to 5 times on a gentle gradient up to approx. 12%, drive-off speed max. 2000 rpm

 

Brakes are best when Bed In much more aggressively then the OEM's suggest.

http://www.stoptech.com/tech_info/wp_bedinstock.shtml

"For a typical performance brake system using street-performance pads, a series of ten partial braking events, from 60mph down to 10mph, will typically raise the temperature of the brake components sufficiently to be considered one bed-in set. Each of the ten partial braking events should achieve moderate-to-high deceleration (about 80 to 90% of the deceleration required to lock up the brakes and/or to engage the ABS), and they should be made one after the other, without allowing the brakes to cool in between."

I just got done doing this on the Mini a few days ago. For the clutch so long as your not slipping it no harm will happen.

It's also a reason why doing it on a dyno works so well. Brakes are not used and you can take the car to 2-3K very easy before you drop the hammer.

I've never has a problem doing it this way.