I put (what i remember as) 5w-30 (or 20) into my 1983 z28 motor becuase thats what the oil dip stick said only to use, but i think its not the right dip stick for the model, so what oil should i use for the engine, (its a 305 C.I. low output)? (mostly summertime driving). I use valvoline, or Penzoil. Nothing synthetic, just the suggested manufacturer oil.
Thanks!

I think the 5w-30 should cover it unless your engine has excessive miles or runs hotter than normal for some reason like towing.

Some engines that have had a rough life and are well over 100,000 miles like a thicker oil like 20w-40.

5w-30 is fine.

Well the guy i bought it off of said it was rebuilt, but he also said it was a 350 bored to a383 ci, and i found out it was a 305. It seems to run strong so ill stick with 5w-30 unless any complaints

10W-30 is the recommended weight. 5W-30 is fine, especially if operated in cold weather.

A real synthetic would be much better, of course.

Yeah I would suggest 10w30, over 100,000, and synthetic if you continue to run it , every oil change . . . Buts its also like what tire pressure should you run as well . . .