What does everyone think of 5w-50 synthetic or heavier oil (15w50) in a 95 bmw 525i with thr 6-cylinder m50 tu engine with vanos? I was thing specifically about Pennzoil platium 5w-50. currently using Mobil 1 Truck and suv. I think it is 10w40 and uses no oil between 4,500 mile oil/filter changes. These cars were originally speced for heavy weight conventional oils? I have tried 0w40 Mobil 1 and engine was just louder sounding and had high anounts of lead in oil analysis. Lead lowered with heavier oils. Just looking for opinions.