Non-detergent oils don't foam up as easily as detergent oils, that's
why they're recommended for motors like compressors and lawnmowers
where the crank splashes the oil up on the cylinders.
You can find 30wt non detergent oil at any stores lawnmower department,
The rings and seals in most compressors are no different than your car.
Be careful about stnthetic oil if you paint, synthetics get by the rings