The MPG for a 1970 Chevy Caprice Classic varied significantly depending on the engine size and drivetrain (2-door, 4-door, etc.). There wasn't a single published MPG figure. You'd likely see figures in the
low to mid-teens (mpg), possibly ranging from 12 to 16 mpg in city driving and slightly better on the highway.
Keep in mind that these are estimates and real-world mileage would depend on driving habits, vehicle condition, and tire pressure. There's no official EPA rating like there is for modern vehicles.