hi every one , the owner for my car before me used 5w50 mobil1 and he said to me dont put another .is this right or i have to change it to 10w40 ? and if i must change it what i have to do ? have i need to clean the engin before i use another oil ?

thaks

Just drain, renew filter, and fill up

The oil type is somewhat dependent on where you are in the world (climate).

i live in Russia its cold winter is here but about summer normal summer , so u mean i have to change it in the summer ?