5w40 or 20w50?

[knowleqe]

hello everyone, i have been using 20w50 in my '98 240sx with 75,xxx miles. my mileage is hurting a bit and i wanted to know if i should switch over to a 5w40 oil. keep in mind i am in southern california and participate in various road racing events. switch to 5w40 or a similar lighter weight oil for everyday putting around; then switch to 20w50 for track days? and should i switch to synthetic? i currently use chevron supreme.

[InsanityInc]

If you go to a track, just use 10w30 synthetic. You don't need high viscosity for a track day, you just need an oil that won't break down under high heat, and that's what synthetics are for.

[hek1620]

i use 10w30 mobil syntec all the time. am i not using the right oil?