One of the more controversial topics within the automotive world is how to properly break-in an engine. There are two camps - 1. follow the owners manual 2. run it hard the first few miles. The common denominator among manufacturers is keeping the RPM's varied and never exceed 4k rpms. Engineering Explained did a nice video of why you should follow the owners manual. I did some searching and found a good explanation from a Porsche engineer that makes sense and confirms why they want you to stay below 4k rpms. *Unfortunately for me, my car had 63 miles on it already so I have no idea how it was broken in. The Subaru had 3 miles. In bold is the anwer: New Engine Break-in Conundrum By: Ken Koop Since I was a young boy, I have always wondered why it takes so long to break-in a new engine-especially those built by Porsche. Most people driving new cars also do not fully understand the real reason for the break-in period. Are you one of them? A good friend of mine just picked up his brand new 911 Turbo and complained about the break-in period taking so long (2,000 miles, not exceeding 4,000 RPM). We have talked about this issue many times over the past few years, always coming up with many scenarios of why such a long break-in period is required. However, we have never agreed on a reasonable answer. Well, you are about to find out the reason Porsche requires the break-in period it has today. The answer comes directly from the engineers at Porsche. I was on a recent Porsche factory tour and was watching an engine being built and dyno tested. Each engine is built by a single person on a moving production line. Porsche feels that they can obtain better quality control with one person building an individual engine from start to finish. In addition, each engine builder can assemble every type of production engine that Porsche produces and every gasoline engine is still built at the Stuttgart factory. It takes 2-3 Â½ hours to assemble each engine, depending on the type. Afterwards, the completed engines are either used in the cars produced at the Zuffenhausen factory or are boxed up and shipped to Leipzig (for the Cayenne and Panamera) or off to Finland (for the Boxster and Cayman). Before all of the parts are assembled for a particular engine; the pistons, connecting rods and valves are individually weighed and grouped together using similar weights to optimize performance. They are put onto a cart that moves along the assembly line with each engine block. This cart contains every part required to assemble that particular engine which includes each washer, nut, bolt, bearing etcâ€¦ As a result, if any part is left in the cart at the end of the assembly line, then-Houston, we have a problem!At the end of the assembly line, the engine is filled with Mobil 1 Synthetic Oil. Each engine is then dry run (without fuel), pressure tested and checked for leaks. Every car coming off the production line is also run on a rolling road dyno. This enables all cars and engines to be tested at highway speed before they leave the factory. Some of the engines are also randomly selected to be tested on a dyno stand before they are installed into the car. The assembly plant has 5 dyno rooms located directly off the production line. The day I was on the tour, there were around 40 engines lined up on dollies. Some of these engines were in the process of being tested for quality control purposes. Once the engine is bolted onto the dyno, warm water is circulated throughout the engine to bring it up to temperature. The operator then starts the engine and checks for the correct pressures and temperature before the actual test begins. Engine speed is then increased in RPM steps to about 80% of its red line (the engine's maximum RPM). The entire engine run takes around 30 minutes. Since each engine type (Turbo, GT3, Boxster or Carreraâ€¦) has a different red line, all of the data is recorded and analyzed after the test is completed.After the engine is turned off, the engine is again checked for seal leaks and its actual HP is compared to its advertised HP. To pass final inspection, the engine has to develop, at a minimum, 100% of what its advertised HP rating is. Also, the engine cannot produce more than 5% over that same advertised rating. If the engine falls out of those parameters, the engine is rejected and then torn down to determine why it did not deliver the anticipated HP. When the test was completed, a Porsche engineer came over to review the results. I couldn't resist asking the question that I had been searching to find an answer to for all these years. I asked "why does Porsche feel it is safe for a new engine to run at nearly full throttle in the factory, while the customer must keep the engine speed to no more than 4,000 RPM for a 2,000 mile break-in period?" I thought that was a logical question and if I do say so myself-well stated! The engineer replied, "Herr Koop, you do not understand (that I already knew). When we do our engine test, the metals inside the engine never reach the temperatures they would when driven on the street since the test session is fairly short. In other words, the bearings, pistons and cylinders never get a chance to thermally expand to their maximum. Therefore, there is little wear on the moving components. But when you drive a car on the street, the engine parts expand considerably more because of the heat being generated from the engine running for an extended period of time. No matter how tight the tolerances are, there is always a slight amount of expansion in the material. The moving parts can wear quickly if exposed to excessive heat and not always in a uniform way. We also constantly vary the speed and allow the engine to run at both high and low RPM's". "Porsche wants the engine to break-in slowly, which means it needs to maintain a lower operating temperature (below 4,000 RPM) and to allow all parts to adjust (wear-in) within their own thermal expansion parameters. This is also the reason why Porsche wants the owner to vary the RPM throughout the break-in period; therefore the engine doesn't get use to one operating temperature range". "Porsche has been using Mobil 1 Oil since the early 90's. With its superior lubricating properties, it takes many miles of driving (without getting the engine too hot) before the components actually seat (or break-in). Porsche's own tests reveal that after 2,000 miles have been driven, all of the moving parts have had a chance to wear into their adjacent surfaces and then an increase in engine RPM is permissible." I replied, "JA DAS SOUNDS GUT, when you explain it that way, it makes a lot of sense." I thought to myself "You Dummkopf, why didn't you think of that". The engineer commented that there were many other moving parts other than the engine that needed break-in as well. Wheel bearings, constant velocity joints, tires, brakes and transmission were just some of the other components that were mentioned. So breaking it down into layman's terminology, it all comes down to; higher RPM equates to more heat, which leads to greater expansion. For a new engine, that can mean uneven wear on certain parts if excessive heat is allowed to build up. In Porsche's opinion, the thermal expansion of different parts and various materials need time to adjust to one another. Porsche's time frame for that to occur is calculated to be 2,000 miles, with the heat restriction being 4,000 RPM. So simple; who woulda thunk. Many experienced Porsche engine builders and experts on the Flat-6 engine state that the peak power of a Porsche engine is developed around the 20,000 mile mark. This coincides with the principle of what the Porsche engineer was telling me; "Break it in correctly and the engine will last longer and perform better". It only took me 45 years to find out the real answer to this puzzling question. After I returned home, I explained this to my friend. As for our ongoing debate, we now feel a solution to this riddle has finally been reached. Neither one of us had the answer to this complex question totally figured out, but we were on the right path! I am finally able to resolve another one of my life's unanswered mysteries and now it's been crossed off the list. I hope this helps explain one of your unanswered questions in the car world as well.