What viscosity do I choose?

[Elysium <wonchung@xxxxxxxxxxx>]

Hello, Bimmers.

I plan to put synthetic oil(mobil 1) into my baby.

However, I don't know what viscosity I should choose.

So far, the dealer puts Castrol 20W50.

I live in Indiana state. You know, here is mild weather.

Could you give some advices which one I choose.

Thanks in advance. 
Please send an email privately.

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