I've been running mostly sm/sn rated oils in my 2 antique daily drivers, plus my lawnmower for the past 13 years, without any issues. I've put just over 100k miles on the 76 350 since it was pulled from the junkyard (not rebuilt - just a timing set and some gaskets etc), and I've put 77k miles on the 83 Caprice in the past 10 or 11 years (total of 240k miles now). The Olds runs as good or better than when i first got it. The Caprice is getting a little tired, but no camshaft issues, just some cold start piston slap, and bad valve seals (for the second time). I did used to use zddp additives or higher zddp oils but I stopped worrying about that several years ago and it hasn't come back to haunt me. If I upgrade the camshaft with something with a bit more lift I will start using something like Valvoline vr1 or amsoil z rod, etc but until that a stock low performance flat tappet engine is fine on any modern oils. Who knows, maybe these engines would have worn out a lot sooner if it wasn't for the modern oil.
Originally Posted by MJ_Massey
So for these old engines, would you go with an SJ rated SAE30 instead? Or would you jump to the latest SN rated SAE30?
Originally Posted by caprice_2nv
Even in my old engine's i would rather have a modern oil that can meet modern specs. A little more zddp would be preferable but meeting sn is probably a safer bet than going with a 30+ year old spec.