318 Oil engine Current specification

The word you are looking for is viscosity
Viscosity is how smooth a fluid runs

For instance, if you are at the beach and you knock over your water bottle, almost all of will spill out

But if you knock over your sun tan lotion, most of it will stay in

Because they have different viscosity

Now, a dual weight oil, 5w30 for instance, flows different at different temperatures then a straight weight oil

Given the climate you are in, I'd say straight 30 is fine

A bigger concern would be conventional oil or synthetic

The actual oil particles in synthetic oil are smaller, so it may seep past seals that conventional oil does not seep past