Before the first BMW M2 CS in the country made the start line for our 2021 Performance Shootout, we needed to add all-important mileage on a drive from Johannesburg to Cape Town. In so doing, we were privy to BMW M’s usually secretive running-in process. Here’s what we learnt from the experts about running in a box-fresh vehicle.
By: Graham Eagle and Ray Leathern
“Running in. Please pass.” Older drivers may remember the signs mounted inside rear screens of slow-moving vehicles, holding up traffic as their drivers rigidly adhered to the running-in routine prescribed in their owners’ manuals. This wasn’t an unusual occurrence as owners understood their vehicles needed to be carefully run in to ensure reduced oil consumption and increased longevity, while also accepting that the original engine oil would need to be changed after the first 1 000-2 000 km.
Running in a vehicle is primarily about the engine, and the recommendation to drive at lower speeds and to avoid using full throttle is intended to ensure mating friction surfaces seal against each other with minimal leakage or rotate against each other with the lowest possible friction.
The final machining process for cylinder bores is known as honing and is intended to create a fine cross-hatching pattern on the bore surface, consisting of a series of peaks and valleys. These peaks are the high points of the cylinder bores and the contact point of the piston rings. During early running, the tops of these peaks are sheared off – creating a plateau effect – effectively increasing the bearing area of the piston rings. This increased area improves piston ring sealing and makes it easier for the rings to glide over the surface on the film of oil which is retained in the cross-hatching valleys.
With the sealing of the piston rings to the cylinder bores being critical for both engine performance and longevity, it is important that this initial wear occurs smoothly and evenly, at consistent pressures and temperatures. Adhering to lower engine speeds and engine loads while the engine is new allows this initial wear to take place in a controlled manner. Drivers will be aware of their “tight” new engine gradually loosening up and revving a little smoother and easier as these surface imperfections are worn away, reducing friction and improving piston ring sealing.
This initial wear also results in microscopic metal particles entering the engine oil, in addition to any residual swarf created by surface tears and folded material from the machining process which might not have been properly removed before the engine was assembled. These metal particles circulate with the engine oil, accelerating the wear of bearings and other lubricated surfaces. Manufacturers thus specify an early oil change, to coincide with the mileage when the initial surface wear and sealing of piston rings would have been completed. The rate of engine wear reduces considerably from this point on, and any further metal particles created will be safely removed from the circulating oil by the magnetic sump plug and oil filter.
Running in brakes is also important as new friction materials bed themselves to newly machined surfaces. It was important to avoid excessive temperature build-up while allowing the surfaces to properly bed-in to each other and thus ensure smooth, consistent performance without juddering or vibration. Brake performance is also compromised during this bedding-in period.
While not requiring a specific procedure, the various bearings and gearsets in the vehicle also benefit from the engine and brake running-in procedures, as they allow the early wear of surface imperfections to take place at lighter loads and temperatures.
Do modern cars still need to be run in?
If you had to drive a brand-new, low-mileage car off the dealership floor tomorrow, you could rightfully ask whether stringent running-in requirements still apply. After all, “Running in, please pass” signs have long disappeared and that initial oil change is no longer specified on anything other than a high-performance vehicle …
Modern manufacturing processes mean that more durable surface finishes and much finer tolerances can now be consistently achieved in volume production. Improved coatings of both piston rings and cylinder bores – combined with better control of their surface finishes and advances in oil technology – have resulted in quicker sealing of piston rings to cylinder bores. However, with the high priority on oil consumption reduction to minimise exhaust emissions and catalytic converter contamination, it is common to find that vehicle manufacturers still recommend a period of running in for new vehicles.
Details are usually included in the owner’s manual, with the least onerous procedures often only specifying “normal use” for the first 500 or 1 000 kilometres while noting that excessive speeds and loads should be avoided.
However, several manufacturers still provide more detailed running-in procedures. These vary depending on make and model, of course, but typically they would cover the first 1 000-1 500 km and include the following recommendations:
- If possible, avoid short trips which do not allow the engine to reach normal operating temperature
- Avoid using full throttle to limit engine load
- Limit engine speed to 3 500-4 000 r/min (petrol) or 3 000-3 500 r/min (diesel)
- Vary engine speed within the above limits, by frequently shifting gears where possible
- Avoid use of the speed control as this will maintain a constant engine speed and will also use wider throttle openings to maintain speed on gradients
- Avoid towing as this increases load on the engine and transmission components
Manufacturers of high-performance vehicles – which are built and bought with the expectation of being driven hard – often provide specific and detailed running-in procedures, allowing drivers to progressively increase engine speeds and loads until maximum performance can confidently be used. For example, the BMW M run-in procedure covers 2 000 km, limiting engine speed to 3 000 r/min for the first 500 km, stepping it up in 1 000 r/min increments for each further 500 km, with short bursts of full throttle allowed during the last 500 km. The importance of proper cooling down is also emphasised, with two kilometres of low engine speed recommended before stopping after a long journey. Permitted use of the carbon-ceramic brakes also increases progressively, moving from light application to medium application, and finally increased full braking, while again emphasising that sufficient cooling is allowed between applications.
In the case of many supercars, a controlled engine run in, either on an engine or rolling road dynamometer, followed by a test-track shakedown, is often the final stage of the production sign-off process. This then allows the customer to exploit the performance of their new purchase immediately after delivery.
How should I run-in my new car?
In practical terms, how does one go about running in a brand-new car? After all, it is probably your everyday car used for your daily commute and the school run. While it is easy enough to avoid sustained high speeds or towing, you will still need to combine the recommended running in with your typical use of the vehicle.
With most of us living in suburban environments, this will mean running in your vehicle at speeds dictated by the traffic. While excessive idling is not ideal, in-traffic driving provides the opportunity to frequently use the maximum permitted running-in engine revs, at light loads in the lower gears. This weekday running can be complemented with a country trip of a few hundred kilometres over a weekend, which we would recommend as it provides a good opportunity to better understand the driving characteristics of your new vehicle. This should not be a freeway trip at a constant speed but rather on quieter secondary roads where you have the opportunity to drive at various speeds in different gears and also to frequently use the brakes – both light and medium applications – while always allowing sufficient time for cooling down between applications.
It is important to remember that if your new vehicle is turbocharged – which many are nowadays – it will typically develop its maximum torque in a band between 2 000 and 4 000 r/min. This characteristic permits using throttle instead of a downshift to overtake or climb a gradient. As maximum torque means maximum engine load, this driving style needs to be consciously avoided during running in; rather shift down a gear and use part throttle at slightly higher engine speeds.
A counter viewpoint exists that running in a new engine is no longer necessary in a modern engine. However, the consensus among manufacturers, especially those of high-performance cars, is that a period of running in is still necessary and new vehicle owners are strongly advised to follow manufacturer recommendations or these guidelines to ensure optimum engine performance and longevity.
