by Jim Kerr

I am asked this question at least a dozen times a week: “how should I drive my new vehicle to break it in?” Breaking in of a new vehicle is a straightforward process but there are many stories told about how to best do this. There is some truth in many of the stories but to separate fact from fiction, we should look at why we need to break a vehicle in.

A good friend often jokes that there is no such thing as “breaking in” a new vehicle – it is just the start of “wearing it out!” There is a little truth here too. The process of breaking in a vehicle means driving it so that parts can wear into each other. Usually, people think the engine is the only part that needs any break in period, but transmissions and drive axles also can benefit from a break in. So how should I drive the vehicle?

Start by avoiding heavy loads on the drivetrain. Full throttle starts, towing trailers, and loading the vehicle with heavy loads place extra force on all moving parts in the drivetrain. When parts are manufactured, their surfaces may look smooth but under magnification, we can see many “hills and valleys”. Lubricating oil forms a thin film that separates moving parts so they do not touch. If there is a loss of lubrication or a heavy load placed on the parts, the high spots (hills) may push through the oil film and touch the other part. This causes wear.

The break in process allows the highest of these hills on the parts to wear down under light load so they do not damage other parts. As the parts move, they are polished so that there is less chance on high spots penetrating the oil film when a load is placed on the vehicle.

The manufacturing processes used today are light years ahead of vehicles from the 1960’s and 70’s. Component finish is better, internal clearances are closer, parts tolerances are more accurate, and materials are better quality. The thousands of miles needed to break in an older vehicle are no longer needed. Instead, it is the first few hours of operation that are the most important. By the time a driver has driven a few hundred kilometres, the vehicle is ready for regular driving.

When starting a new vehicle, engines should not be idled for long periods of time. Oil pressure is lower at idle speed and parts that depend upon splash lubrication may not receive enough oil to prevent high spots from pushing through. Full throttle operation should also be avoided. It places heavy loads on components and high spots can score other components, accelerating the wear. This doesn’t mean you need to baby the vehicle.

Drive the vehicle as if you were trying to achieve good fuel economy. Light to medium throttle acceleration is preferred, and keep the engine rpm’s in the bottom half of the rpm range. On many engines, this would be below about 3000 rpm for the first few hours. Occasional three-quarter throttle acceleration is fine, as the increased gas pressure in the combustion chamber helps the rings to seal.

Avoid “lugging” the engine. Driving in too high a gear at low speeds makes the engine work harder. It is better to have it running a little faster with less throttle than too low an rpm with more throttle. Modern engines don’t need to be driven at slow speeds. Keep up with traffic and drive the speed limit. I wouldn’t recommend towing a trailer with a brand new vehicle, but it is done sometimes and the vehicles seem to last well.

Some say that drivers should vary vehicle speeds during the break in period, driving only a few kilometres at one speed. This isn’t necessary. If you are going to be driving on the highway, backing off the throttle every few kilometres and letting the vehicle decelerate for a few seconds will pull extra lubrication into the upper engine cylinders and intake valves.

Breaking in a new vehicle isn’t a tedious or time consuming process. Drive it normally and with care for the first few hours and it should be ready for many more kilometres ahead.

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