E34 525i M50 engine, Texas - Oil choice?

Using 5w-40 synthetic blend at 160k miles, summer time in Texas. Any other Texas or Southwest USA drivers using a thinner oil and happy with the results?
Possibly using German Castrol 0w-30 upon next change (around September)...
Thanks in advance...
David in Sugar Land
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many board members here... http://www.bimmer.info/forum/forumdisplay.php?f  use mobil 1 0w 50 (or 0-40 - I forget!) they love it. by the way, that is the BEST board for e34

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