so i have this old 1999 subaru impreza outback sport beater with 250,000+ miles on it that i let my friend drive around and it is starting to burn oil, it does 5,000 mile oci's with maxlife and and at around 3,000 the oil has gone down about 3/4 of the way between the full and add mark. it is driven around 400-500 miles a week. i added some rislone stop smoke recently and noticed the engine runs smoother. the owners manual recommends 5w30, would it be recommended to switch to a thicker viscosity? if so which weight?