G-unit.
A Synthetic multigrade Diesel engine oil 15w40 weight should be used and your brands of product would be more specific dude !
Mobil Delvac lines are normally used for stationery motors such as gen-sets, so your source availability tends to be important ?
Understandably the BMW 2.5ltr TD donk is normally designed to operate in lower european climatic tempreture conditions, so changing to an 85 degree C opened thermostat is a common improvement done to imported vehicles in Australia/New Zealand.
Cheerio,
Vinniman
'88 Highline
Perth, W.A.