How should you 'break-in' a new car?

Breaking-In a New Car
Most manufacturers have recommendations in the handbooks.

Basically you start off treating the engine very gently i.e. gentle revs and never more than 1/4 throttle. Over time you gradually use more revs and more throttle until you eventually end up using the full range of the engine. It is important to eventually end up using all the power and rev range to wear harden various parts. It is also important that you do not keep to a single continuous speed or gear but vary your speed quite a bit during this time (a long highway journey is NOT a good break in if you just sit in top gear at a continuous speed). This is because things are still hardening up and you can wear a groove into them.

Modern engines break in relatively quickly, often 1000km, older designs took longer as the tolerances were not as precise. The first oil change is often a lot sooner than later ones as during break in rough edges from manufacturing will be worn off and end up in the oil.

Here is more advice from various contributors:

Drive it gently. General rule is not to exceed 3000 - 3500 rpm. for the first 500 miles. It is also a good idea to be kind to it for the first 2000 miles.

"Breaking in" your cars engine is an old myth, it is also bull. Rule #1 if you want your engine to last a long time, treat it gentle all the time, not just for the first 1000km.

Break in is important. All engine bearings and cylinders, etc. must wear evenly and proper. Also, piston rings need to seat. Have you ever seen a new engine burn oil until it breaks in? Some piston ring take up to 5000 miles to fully seat or wear evenly to cylinder bore. Not following proper break in procedures could result in premature engine/parts failure.

This depends whether you purchase or lease a car. With a purchase you should break a car in for the reasons and using the methods described before, ignoring the one comment about it being bull. If the vehicle is a lease you may skip the break-in period if you so wish. Since not breaking-in a car may result in improper wear of parts, or even engine failure, during the warranty period it will be covered, and a leased car will be returned to the dealer before the warranty period expires.

You shouldn't just break-in your car if you are buying it. Even if you are leasing it you should. Do the next guy a favor. A very inconsiderate answer man. Besides some people lease it and then decide they like it and want to buy it, so I say, you should break it in anyway. No matter what.

If you research on how to break-in a new engine on the web, most sites will tell you a procedure to break-in the piston rings (the only thing that matters).

The proper way to break in an engine is to drive at 30 mph and accelerate to 50 mph. Do this to break in the engine the proper way. Do this the first 3000 miles or so.

Manufactures are making engines with much higher tolerances today. Where cylinder clearances used to be in the thousands of an inch, now its in the ten thousands. Bores are rounder and straighter. There is know reason to baby a newer engine, it will actually hurt. You need cylinder pressure to drive the rings out onto the bore, which actually shaves the bore into a perfect fit. By babying it the rings will only rub and burnish the surface leaving a less then Ideal finish. So ... keep the revs below 4000 the first 300 miles, then drive it ... accelerate with meaning for the next 2500 miles and your all set. This is how all High Performance engines are broken in, and all engines today can be considered a high performance engine since they pull more power out then there predecessors ever did.

Most modern car engines are broken in at the factory, before assembly. Therefore the old tradition of breaking in a new car doesn't apply anymore. Just drive as you normally would drive and treat the car the way you would treat anything else of value.