What's the period called when you first buy a car and you have to go slower than usual to get the engine working properly in the future?

Can it be used in another meaning? Because in my language you can use the same word to define a period where you have to pay particular attention to something (in this case, pay attention to the speed of the car).


2 Answers 2


When you buy a new car, you're supposed to:

  • drive at a variety of different speeds
  • avoid hard acceleration
  • avoid long drives at the same speed (such as on the highway)

In American English, this is called the break-in period for the car, or more specifically for the car engine. This term is commonly used for machinery. The break-in period is the time in which you are breaking in the engine.

The term is also used for clothing, particularly leather clothing which can be very stiff until it is worn for a long time.

Note that the term is meant to evoke a physical process acting on a physical object. It does not specifically imply that the user needs to pay greater attention or act with more care during the break-in period.

As per the comments: In British English, this is called the run-in period for the car, the time in which you are running in the engine. The phrase "breaking in" is reserved for animals (such as horses).

  • 8
    Breaking in is an American term for British running in. In Britain, breaking in might be understood to apply to a horse but never to a car or a car engine.
    – Anton
    Sep 15, 2020 at 23:07
  • @Anton I clarified that this phrase is an Americanism. Sep 16, 2020 at 1:04
  • 4
    Running in is the British expression, breaking in is American, as Anton says. Sep 16, 2020 at 8:14
  • 2
    Break-in (mechanical run-in) (Wikipedia) Sep 16, 2020 at 13:57
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    One additional point - "breaking in" in the UK is very likely to be confused with burglary ;) Most people don't train horses or know anyone who does. People are very familiar with the idea that if someone breaks in, it's probably to steal your car radio. Sep 16, 2020 at 17:20

It’s called breaking in the engine:

What do we mean by ‘break in’? It comes down to giving the engine time to adjust and operate evenly after rolling off the production line, so no parts are put under excess strain early on. — 6 Ways to Break in a New Car Engine

This definition is also listed in Cambridge, with the British English equivalent being “run something in”:

If you break in a vehicle, you use it carefully and slowly for a short time when it is new, so that you do not damage its engine.

See also Wikipedia: Break-in (mechanical run-in)

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    I have only ever heard run in in the UK. e use break in for shoes and horses.
    – mdewey
    Sep 15, 2020 at 17:25
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    Yes. "Breaking in" is a purely North American usage. Always "running in" for British motor vehicles. When I was a kid people used to put "Running in - please pass" notices in their rear window. With modern engines you don;t have to do this so much. Sep 15, 2020 at 17:55
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    AU commentator here: We'd understand 'running in', but would be more likely to use 'breaking in' - just like with shoes and a range of similar items, eg:computers for the period between bringing home the machine full of factory settings to when you have set up desktop backgrounds, shortcuts, etc. Breaking in of horses is a slightly different concept, methinks - actually breaking their spirit, rather than wearing it down.
    – mcalex
    Sep 16, 2020 at 9:34
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    @mcalex In the UK (and I think also the US) you don’t break in horses, you just break them.
    – Mike Scott
    Sep 16, 2020 at 9:51
  • 1
    @MikeScott - UK site: "As a rough guide it normally takes 3 – 4 weeks to have the horse broken to saddle". Sep 16, 2020 at 14:31

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