When to change degree of engine oil?

Hello friends of this very good page.
Have if there is any good understood in the matter that can get me out of doubt.
I have a Nissan V16 2009 with 250,000km (collective locomation) In excellent motor condition using 10W40 zero problems, there is someone to change myself to 20W50 according to the mileage that the vehicle has, but what I have understood that degree of oil would be for a worn engine, which consumes oil, I use it in a Toyota Corolla 1988 (288,000km). When using a 20W50 oil I would not have problems with the taes, since according to the user manual the only oil that should be used is 10W40. It does not specify the mileage. Is it convenient to change degree or does it depend?

I am not a friend of the changes of degrees in the oil if of its quality, in ancient engines where the olgures were more ex -sajesa would be liked in the case but I do not like it, it continues with the 10 if the engine sounds or something is for a wear that must repair, the taquies are delayed more to load with a 20 that with a 10 mileage that you have could affect you in a greater way, leave it with the one who has and nothing else, with the biscocity sypo the oil is changed hahaha

That is, if the engine is well with the 255,000km I must continue using 10W40, that of looking at the mileage would not be the case.

Kikemec Gacias

What Nissan brings xauxas, coins or chips can tell you that they are regulated, but if you have no problem in the vehicle continues with the same oil

Ok then as a general way to continue using the degree of oil according to manual. Unless the engine is very worn and consumes a lot of oil or is pulling blue smoke, of course as a last instance before repairing engine.