Using thicker oil
 

It's now time for an oil change on my '95 Civic. The owner's manual I
downloaded recommends 5W-30, but here in the Philippines all I can
find is 10W-40 and 10W-50. People look at me strange when I ask for
5W-30.

We're located very near the equator, very hot tropical climate and it
never snows; is it safe to use the thicker viscosities? Will it affect
mileage noticeably?

BTW: Does it even make sense to buy multigrade oils here?

Thanks.