10w-30 or 15w-40?

[Jason M Surprise <jmsurpri@xxxxxxxxxxxxxxxx>]

Kinda confused.  The owners manual for my 94 325i shows 10w-30 is
suitable for -20 through 40deg (f) ambient air temps while 15w-40 shows
0 through 83deg.  Looking at past dealer receipts, it looks like they've
always put in 15w-40.  I'm switching to synthetic and doing my own oil
change this time.  I am inclined to stay with 15w-40, however I was
always under the impression that 10w-30 was the way to go from posts
I've seen on here and other places.  It just seems counter-intuitive
since average temperature around here doesn't get anywhere near that
low.  Are there any risks of running 10w-30?  Does one offer a better
performance advantage over the other?  I'll be putting in Mobil1 if that
makes any difference..

Thanks!
Jason

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