Go for fully synthetic based oil . Use Castrol , Mobil , Esso , Wintershal , or another good oil . Look at the small letters on the back of a package , viscosity is not everything . Look for the letters S*/C* , the star is another letter . The S is for normal fuel engines , the C stands for diesel . The * is another letter like i said and the further in the alfabet it is the better the protection of the engine . That is the real quality of on oil . For example SG/CF is a lot better then SE/CD oil . Even the specs for viscosity doesn't really matter then , only for extreme temp's . When winter in Finland it's better to go for a 0W30 then for a 10W40 . The opposit for Greece where you better can go for a 10W50 then a 5W40 . The first number is a temp indication , the second the visco at that temp .