Well, that's part of my dilemma. When I bought my first Bimmer, it had 214K and was in exc. shape. The PO took it to a spendy indie garage every 6 months (whether it needed it or not). They filled it with Castrol Syntec 5w-50 the whole time.

Castrol quit offering that one, at least here, but they did have 0w-40 which was advertised as being ideal for Euro engines. So I bought a bunch on sale. Later I read that 0w would be good for northern Minnesota or central Canada but too thin for warm climate. The thinness before becoming hot being ideal for arctic climes. And me in Mediterranean Bay Area. DOH! Surprisingly naive me.

And I also found that supposedly if you mix the weight designations it will balance out. So I figured that if I went with two 15w and one 0w, I could use up my stash of 0w.

And it's almost gone.

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Te futueo et caballum tuum

1986 300SDL, 362K
1984 300D, 138K