I'm planning to get a new petrol (gasoline) car soon.
A friend of mine, who worked as a motorbike mechanic when he was young, told me he puts a small quantity (125 ml / 4 oz) of 2 stroke oil in the petrol tank the first time he fills a car.
He argues it helps the burn (break) in of the engine, making the piston ring seal better against the sleeve, or somehow doing tolerance "matter less". I've found information in the web on doing so to diesel engines, but not to petrol ones.
Do you find doing so advisable? Anything to worry about if I do so? Does it sound logical?
There is a related question on breaking in new cars, but not covering this idea.