Cars House

is it a bad idea to use 20-50 in a 318i in california?
where should this oil be used, and does it matter that much?

I have used this oil in warm temperatures and where oil pressure was low. It will boost hot engine oil pressure.

Downside is probably slightly poorer fuel economy due to increased viscosity.

I don't see any harm, however if you have a warranty, be sure it's an option in the owner's manual.

good luck