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The oil was changed before I bought my 524td. I don’t know what oil or weight was used. But would like to do an oil change. I use bmw 5w-30 diesel oil with archoil friction modifier additive in my 328d. 

what oil and weight are you guys using/do you recommend for the M21? I use archoil additive in the 328d as it adds lubricity which helps prolong the life of one of its Achilles heals (the timing chain). Any benefit to using an additive in the M21? 

Delo 400 15w40, but I don't honestly think its that critical so long as its something of reasonable quality. 

These do have a flat tappet cam and (IMO) a somewhat marginal top end lube system. Probably get more benefit out of making sure that oil sprayer is clean than any magic additives honestly but if you want to add something with some extra ZDDP the cam won't hate it. I don't know that its really needed though, diesel oils tend to have more stuff in them that is flat cam friendly than modern gas engine oils. 
 

OK, I don't have a TD, nor have I. But I wouldn't even think of using an oil for a modern engine like a 5-30 in a M21. Pic is from an owners manual scan. Suggests 20-50 for most conditions. Even 10-40 is only good for about 90F. 5-30 appears to be good for -40 to 25F. While these engines were very sophisticated for their time, they and their clearances are ancient now, but while oils have gotten better, I don't know if they've gotten that much better.

Castrol GTX Classic 20W-50

is that diesel oil though?  I thought GTX Classic was for gas engines. Diesel oils have different additive packages, in large part to deal with the soot. 

I run 15w40 because its whats available locally in diesel oil. I can get thinner which this old dinosaur definitely doesn't want, but 20w50 diesel oil isn't on the shelf.  


 

Well, I learned something new. I didn't know diesel took a different oil. Sorry about that.