I know it sounds dumb, but when I went to the auto parts store to do buy oil to do my oil change, they told me I needed a thicker type of oil for my car becasue I'm right around 90,000 miles. But when I did my oil change 3,000 miles ago they gave me a thinner type of oil. Now my dad says to run what the manual says but my 2000 Si didn't come with it. I'm dude for the change this week and want to get it done but didn't want to put stuff in my motor that's going to hurt it. the oil they sold me was 20W-50. If you guys can tell what I have to put in it it would be greatly appreciated. Also it would be nice if someone can tell me the difference of oil thickness and what is the purpose of them. Thanks.