When is a engine fully broken in?

[nielshm]

When can I expect to see best possible milage, feel best power output? 

Some claims 5-6000 miles before every thing performs the best possible, others doesn't really notice any difference. 

Having a new car in the winter is a bit challenging. Cold, windy, rainy weather, winter tyres fitted doesn't help overall mpg. And all is driven by a engine with 700 miles on the clock. 

[Catlover]

When can you expect to see best possible mileage etc? 
Next summer.

then next winter expect cold, windy, rainy weather, winter tyres...... all causing worse mpg etc.

Unless climate changes make a dramatic effect sooner that is.

 

[Cbatoday]

Tbh the engines tolerances are so fine now running in procedures arent the same as years ago

Better oils and engine materials. No more decokes after a set number of miles