When it comes to new car ownership (or even when you have a freshly rebuilt engine), one of the most important things you need to do is break the engine in properly. There are a lot of misconceptions when it comes to this and everyone, from your mechanic to your grandfather, will have their own school of thought- but here we’ll talk about why you need to do it and how we prefer to do it. If you drive something like an A45 AMG that comes with specific instructions (or your mechanic tells you otherwise), it’s best to follow them instead. After all, nobody knows an engine better than the person who built it for you.
Here is where a lot of people differ in opinion. To get one thing out of the way first: most modern engines are tested and spun up to well over their redline in the factory in order to check that the assembly is correct- so limiting your rpm has nothing to do with avoiding damage due to speed. What still matters is that a fresh engine, whether from factory or freshly overhauled, has new piston rings and bearings in it. What you are doing during this critical run in process is wearing these parts in so they move smoothly and seal or develop a proper oil film during normal operation.
Piston rings are not a perfect fit from factory- but they’re not meant to be either. During the initial run in process, the rings wear against the bore and begin to develop their seal against the cylinder wall. The quality of the seal is one of the important parts of engine longevity: if you are too gentle with it or too rough with it, the piston rings will not develop a proper seal and your engine will prematurely lose compression or develop blow-by problems.
On the bottom end, the bearings that sit between your conrod and crankshaft also need to be worn in. This is why some workshops recommend the use of a mineral oil or a specific run-in oil during the first 500 to 1000 kilometers- these oils are specifically designed to help break in the bearings more effectively. As the bearings wear down, the initial run in oil needs to be flushed and you can then proceed to using some high-grade fully synthetic lubricant.
So we’ve established that you need to be gentle during these first kilometres, but we’ve also said that being too gentle brings problems of its own. The key to get around this is progression. For the first 500 kilometres or so, limit the engine to 3000 rpm and try to vary the speed and load as much as you can. The best way to do this is to get stuck in traffic and cruise around town- but whatever you do, don’t hold it at that 3000 rpm limit.
Once you’re past the first 500 kilometres, you can begin to push the engine a little bit harder. This is something derived from motorcycle engine specialists who use this to force the piston rings into sealing more effectively. Once again it’s important to vary your speed and load, but you can get this done on a highway or a quick road trip out of town.
The rate of increase for your limit should be around 500 rpm for every 100 kilometres- so at 600 kilometres you can push it up to 3500 rpm, at 700 kilometres you can push it up to 4000 rpm, and so on, and so forth. By the time you hit 1000 kilometres you should have a pretty wide range of rpm to play with, and your car should also be due for its first service.
The way we’ve described here is only one of many ways to run in your engine. If you look to race teams or some of the fancier manufacturers, they run their engines in on an engine dyno that automatically does what we’ve explained here and usually break their engines in within a day or two. It’s not exactly rocket science, and breaching the rpm limit occasionally isn’t going to break your engine, but it is still important for engine longevity. The other benefit to running gently during these first thousand kilometres is it allows you to stay on top of your car in case any problems begin to pop up.
Now here’s the interesting part: I’ve actually purchased a brand new Myvi and together with the rest of the team, we worked on a little video on how I ran my engine in. This is a small project that we’ve embarked upon, so bear with us as we try to dispel the butterflies in our stomach, especially now that we’re in front of the camera. We hope you enjoy!