What is the difference between 5w-30 and 10w-30? Sorry for the lame question. And what would one do that the other couldn't? (basically which one is better?)

They are both the same oil when your motor is hot (operating temp). It's when your motor is cold is when the thickness changes. 5W-30 is thinner when cold. 10W is slightly thicker when cold. This is helpful in cold climates mainly (on start-up). I personally run 10W-30 all the time cuz my car never see's cold weather. They also say to run 5W-30 when your motor is new with fairly low miles and 10W-30 as it get's older and higher miles, because as an engine gets older it tends to want to leak oil out little places, and 10W-30 is slightly thicker and won't leak in some places 5W will.

Greg Williamson
1999 Eclipse GS "Sport" (Sold)
Star Stage III
12.817 @ 109.36

Good explanation... That might explain why i have to add oil more often since i switched to 5w from 10w?

John 96 GS

Switching from regular oil to full synthetic will also cause oil leaks if your engine has alot of miles on it.

1999 Eclipse RS (all show)
1990 Turbo Eclipse (race)