Use a 5W-30 oil. Do not add anything, ever. Look for the GM dexos certification listed on the container, that means it meets the highest standard of the company that made your car. Walmart has the best price everyday on oils and look for an AC delco filter while you're there ( the factory OEM filter) they carry many of the OEM sizes.
Go with 5w30, it's worked well so far. I don't know if synthetic is really necessary, if it doesn't burn oil then sure, otherwise it's a waste of money.
You can use 100% Synthetic AMSOIL SAE 5W-30 Signature Series 100% Synthetic Motor Oil (ASLQT)
30W is covered by the 5W-30. The petroleum based oils are much the same no matter what brand.
The manufacturer's recommendation is always better than some 'expert'. If you use fully synthetic 5w-30 it will protect your engine the best. Wal-Mart sell it at half the price of Mobil.
Stay with the recommended 5W-30 but look for a high mileage version.
i used Pennzoil for over 25 yrs and i never had any trouble with the engines ! since it has high miles i would advice you to get 10w30 high mileage Pennzoil, that,s what i use in my cars !
What kind of oil to use in a 91 firebird with 200+ thousand miles on it it say on the cap 5w30 but I was told to use 30w pennzoil and I don't know what to do
