Hey, I have a 2008 pontiac grand prix with a 3.8 v6 with 196,886 miles. For the past two years I have used 15 w40 in it because that is what my grandfather told me to use. But now I am considering going back to the 5 w30 that is soposed to be in it. What should I do
Use whatever is in your owner's manual. If you've used 15W-40 for two years, you have at least that much unnecessary wear and tear in that engine. Your grandpa is used to old cars like my '79 Catalina, which has high tension piston rings. It's the complete opposite on most cars nowadays.
What does your owner’s manual say? Use that. It will tell you which type and what specifications/certifications it needs to meet. Brand of oil doesn’t matter as long as those are met. Also, use a premium oil filter with each oil change.
5 w30