I run Castrol enduron synthetic blend 15-40(dad got it from work lol) all year round, or rotella T 15-40, -16 the other mornin, not plugged in, fired right up, good battery and glow plugs, it'll start, and in an older idi, 15-40 is good, winter tho, 0W30 would be better, just for easy cranking