Engine Oil for 91 318i?

[BarF1]

What engine oil would be best for a 91 318i with 180000 kms ?

Highest temp over past year = 28 degree C
Lowest temp over past year = -12 degree C

Brand and weight ? :)

[Fuggly Stick]

The previous owner of my car only used Mobil1 . He used 5w30 during the winter and 15w50 during the summer. The car has about 172000 miles(276807 kilometers) on it and no signs of leaks.