I use Mobile 1 20/50 in all my old cars. 67 440 GTS Dart, 66 426 HEMI charger, and my 66 273 Charger Dart, still being worked on. I Built all of my cars. Just had machine work done, BUT I assembled all myself. Dont need to own a shop to know what is what. But I did turn wrenches at a GM dealer.