Step 1. I have read to thin it with whatever the can lists to use to clean up with, (which is mineral spirits) but I have read here to use acetone with rustoleum paint up to 10% when roll and tip and up to 25% when spraying. I want to spray the paint on an old riding mower instead of rolling it. of Rustoleum Oil-based paint for spraying? Rustoleum makes their own thinning agent, but if I'm not mistaken, it's just a dolled up can of X-brand thinner (mineral spirits) that costs twice as much.
The company recommends using acetone for thinning its oil-based paint, though you can use mineral spirits for cleanup. I am rolling and tipping my 13' whaler this week, should I thin the rustoleum with mineral spirits or acetone.

I've been trying to finish spraying a 60-ft gate/fence out back, and w/o thinning the paint (Hammertone) at least 4:1, it comes out too thick.

I'm using a small electric dewalt paint sprayer that uses the plastic cup that screws into the spray gun. How much acetone should I mix with 1 Qt. Pour 1 gallon of Rust-Oleum oil-based paint into a bucket that holds at least 1½ gallons, to allow room for stirring. Rustoleum comes in spray cans, which is fine for small to medium-size surfaces..
However, if you want to paint something large such as a vehicle, tractor, or other equipment, you are better off purchasing Rustoleum in a paint can and thinning it with mineral spirits before using your own spray gun.