Can someone explain to me why we need to slowly run in new cars? What are the consequences if we don't? will the engine explode or something? :'(

 

I forget the reason why in the 'good ole days' of yore a run-in period was mandated (something to do with O-rings? gasket heads? sealing?) but the dealerships of the last few new cars I personally handled all said that it was no longer a required thing.
In the immortal words of my E39 salesman: "Go ahead. You can redline it off the lot! Won't make a difference with modern engine durability and technology." Now whether or not you would accept that as fact or cum grano salis is up to your interpretation

 

I forget the reason why in the 'good ole days' of yore a run-in period was mandated (something to do with O-rings? gasket heads? sealing?) but the dealerships of the last few new cars I personally handled all said that it was no longer a required thing.
In the immortal words of my E39 salesman: "Go ahead. You can redline it off the lot! Won't make a difference with modern engine durability and technology." Now whether or not you would accept that as fact or cum grano salis is up to your interpretation
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I ran my last 530d in as per the book and will do the same with my new one. I don't mean I drove round like a snail but just avoided using kickdown and full throttle. In the diesels the max revs is 3,500rpm on run-in but as the torque is low down you rarely go up to this in normal driving conditions. With the petrol varients I think its 4,500rpm. The book written by the manufacturer tells you to run the car in and a salesman tells you to trash the shit out of it from 0miles. Erm no brainer

 

Your engine should not explode if you do not generally follow the engine "break-in" procedures. However, if you try to stress the engine to identify the limits of its performance (redlining, racing, etc.), you can cause your engine to fail in a number of different ways (although it probably will not explode, but you may severely damage the engine in doing so).

The concept of "breaking in" new products is generally used to extend the useful life and reliability of the product.

Virtually every device follows a so-called "bathtub" reliability curve -- this means that there are lots of defects/failures when the product is very new (infant mortality) or very old (worn out), but very few defects/failures once the product survives its infancy (i.e., if you look at a cross section of a bathtub, the walls are high, which represent defects/failures when the product is new/very old, and the bottom is low, which represents the useful life).

In many industries, the manufacturers will "break in" their products before they are sold to you to eliminate infant mortalities, since these are very costly to replace under warranty (e.g., all electronic devices, such as microprocessors, memories, etc. undergo life testing in the factory before they are shipped to OEMs for integration into devices). Unfortunately, due to various regulations around the world, auto manufacturers generally cannot "life test" their engines before they are installed in autos and sold (i.e., otherwise, you would buy your car with a certain # of miles already on the engine).

Thus, the first purchaser of the vehicle needs to "break in" the vehicles after purchase. Unlike microprocessors, if your engine has a defect or otherwise fails during its infancy, it can generally be repaired, whereas the microprocessor that fails life test is generally scrapped and not sold.

In other responses, sales people have invited purchasers to ignore the factory recommendations and redline the vehicles. Please keep in mind that many of these same sales people are not known for their honesty in what they say and promise to get you to buy a car so that they earn their commissions for the sale. If they really knew what they were talking about, they may be better used on the factory floor rather than the showroom....