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. 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:

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 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:

All other vehicles
Bed the engine in on 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:

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.