How to break in an engine

Break-in (mechanical run-in)

It is important to be clear on this subject. The oil and motor industries are vast and complicated. I have written this article with the aim of being informative and to the point.

Please watch this short video to see why it is necessary to break in an engine:

There is far more to the technical aspects of bedding in an engine that could be mentioned like the process of piston ring burnishing in relationship to oil blow-by and the use of synthetics as a first fill oil for most modern vehicles, chrome and nikasil bores etc, but that is beyond the scope of this article. There is a lot more information on this subject and on specifications and approvals and lubricant choices that I could have shared. However, this is not a definitive answer to all the questions relating to the correct bedding in of every single engine ever built and the environment it will operate in and the type of use it will be subjected too. Having come from the aircraft industry and having worked as a qualified aircraft technician I still believe in breaking in an engine. However, this belief is not based on elaborate old theories but based on my experience and a modern overview as I see the subject, after 25 years in the oil industry.

An overhauled engine is one where the bores have been machined and new pistons or old pistons with new piston rings have been fitted. The main purpose of break-in is to seat the compression rings to the cylinder walls. Also if new crankshaft bearings are being fitted to run them in.

New car engines

At one time oils for running-in an engine were readily available. A requirement of the engine manufacturer, they were introduced on the road engine build line and replaced after the first 1000 kilometres or so, at the vehicle’s first service. Today of course, with pressures on cost-of-ownership, this first vehicle short service has, in all but exceptional cases been consigned to the history books.

Therefore, in general, with a new car, for the first 1500 kilometres:

  • Drive calmly.
  • Vary the driving with a normal mix of city and highway. Changing engine speed and load encourages the piston rings to move slightly, which helps creates a more uniform wear surface between the ring and cylinder wall.
  • Always note the engine temperature and do not drive a cold engine hard.
  • Avoid hard starts and stops (brake pads must also be bedded-in).
  • Never idle an engine warm, drive it warm.
  • No extended idling.
  • No extreme acceleration.
  • Avoid over-revving the engine, try to keep the engine speed under 4000rpm.
  • Vary your speeds over the full range of city and highway driving.
  • Don’t use cruise control.

When in doubt always consult the vehicle manual. Try not to take advice from the dealership as they usually know even less than you do.

Overhauled competition engines

Road car engines are today filled with factory fill specifications designed to survive to the first major service interval, often 15 000 kilometres or more. In the competition world, however, there is still a very real need for the continued use of running-in oils. Modern oils are so very good in reducing wear that if placed in a new engine, the process of bedding-in the critical areas of rings and cams can take thousands of kilometres to achieve peak performance. In the case of a competition engine and in particular an older, rebuilt unit, it is therefore desirable not to use the best oils initially, preferably Ravenol Break-In Oil SAE 30 or alternatively a mineral oil SAE 30 with 1000 ppm ZDDP (Zinc dialkyldithiophosphates) used for a maximum of 1000 kilometres if the vehicle is being run-in on the road. These running-in oils encourage rapid bedding in of the critical areas. Once bedded in this oil may be drained and the engine filled with a fully synthetic blend if specified.

With a race track like Killarney the break in process would be something like this:

  • Do not warm the car up by idling and revving the engine – drive the car warm.
  • Make sure the car is tuned to a safe air/fuel ratio before any wide open throttle driving is done. Running a car too rich during break-in can wash down cylinder walls not allowing the piston rings to seat correctly.
  • The engine should idle for no more than one minute at any time during the break in period.
  • Do not labour the engine while driving the vehicle.
  • Once the engine is warm take the rpm to one third of the rev range for three laps.
  • Do not operate the engine for more than 5-10 minutes (three laps at a third of the rev range should take around about 6-7 minutes). Vary the engine speed and loads. Changing engine speed and load encourages the piston rings to move slightly, which helps creates a more uniform wear surface between the ring and cylinder wall.
  • Let the engine cool down to cold.
  • Laps four to six take the vehicle to two thirds of the rev range. Lap seven, eight and nine take the rpm to the red line in a couple of gears, not all of them, every second or third gear. After accelerating get off the accelerator and while still in gear, let the engine slow the car. Lap ten, eleven to fifteen operate the engine through the whole rev range, careful not to keep the engine in the red for longer than a few seconds at a time.
  • Allow the engine to cool down to cold after lap fifteen.
  • After lap fifteen the engine is ready for competition use.
  • Change the engine oil after fifteen laps to your choice of synthetic oil, preferably a 5w/40 competition oil or the viscosity that the OEM recommends. There are racing oils available in SAE 5w/40, 5w/50, 10w/50, 10w/60 and 15w/50.

All other vehicles

Bed the engine in on Ravenol Break-In Oil SAE 30 or alternatively mineral oil SAE 30 with 1000 ppm ZDDP (Zinc dialkyldithiophosphates) used for a maximum of 1000 kilometres. Do not exceed 1000 kilometers. Then change the filter and oil and replace with the OEM’s choice of mineral or synthetic oil.

In general, for the first 1000 kilometres:

  • Drive calmly.
  • Do not labour the engine.
  • No extended idling.
  • Never idle an engine warm, drive it warm.
  • Always note the engine temperature and do not drive a cold engine hard.
  • No extreme acceleration.
  • Avoid hard starts and stops.
  • Don’t use cruise control much, if at all.
  • Do not take on a long journey at a constant speed like travelling from city to city on long freeways.Changing engine speed and load encourages the piston rings to move slightly, which helps creates a more uniform wear surface between the ring and cylinder wall.
  • Vary your speeds over the full range of city and highway driving.
  • Avoid over-revving the engine, try to keep engine speed under 4000rpm for the first 800 kilometres.
  • Use the full rev range after 800 kilometres without over-revving the engine.

Generally, don’t baby the car but don’t beat the car to death either.
A good variety of driving conditions is the best for engine break-in. 

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