From an oil guy out here, ( Shell / Total fina elf )
I own an India spec AVL500, almost the same architecture and innards as u.s and europe spec engines except for carburation setup for various destinations.
Oil : Primarily is meant to lubricate and minimize friction among moving parts in an engine, apart from cooling & acting as a heat transfer agent, plus provide added protection through an additive package ( Mainly - Detergents- to clean carbon and soot deposits ,Dispersants- to keep the cleared muck in suspension till the next oil drain, Anti wear agents like Zinc Di Thio Phosphate popularly known as ZDTP, Viscosity modifiers- to modify viscometrics of an oil across varying operational temperature ranges, Pour point depressant : to enhance the flow properties of an oil at minus temperatures etc....etc. )
These are the standard additive package in any brand of oil, regardless of viscometrics- 0w30 , 5w30,15w30 or 40, 20w50 etc
Diesel grade oil characteristics are API classified as C ( COMPRESSION ) and range from CC,CD,CE,CF,CG,CH,CI,CJ......the higher you go the better detergent, dispersant, antiwear characteristics, it possesses. again regardless of viscometrics ( 5w40 / 20w50 etc )
Gasoline/Petrol grade oil characteristics are API classified as S ( SPARK ) and again range feom SC,SF,SG,SH,SJ,SK.....regardless of viscometric.
So over all i would say a CF/SG spec 20w50 of any make would give sustained lubricating and cleaning properties over ambient temperatures ranging from +49 C to -5 C
Google any brand of oil available in your area, and check for the Technical Data Sheet for an available viscometric, eg. ( 5w30,0w30,15w40,20w50 .....)
Check for Flash point - Pour point temperature - TBN number ( its higher in diesel specs because it indicates acid neutralizing properties- a safe figure for our engines should be 10.5 )
Drain your engine oil & replace the oil filter at 2000 miles max, religiously and am sure there wont be any oil related issues with your steed.
Cheers.
R.D.