Adding acetone to fuel to improve mileage has been widely debunked as a myth and potentially harmful to your engine. But good luck with it.Fitch fuel catalysts have always worked well for me. I've gotten up to 5 mpg more by installing them. I usually put one on every vehicle I own. A slight bump in power is a bonus. As of right now, they don't offer for FIAT, but I'm waiting on them to get back to me to see if they have a universal that might work or if they are developing one for us.
Now I don't recommend this to anyone unless you research extensively and trust what you're doing, but I added Acetone to my fuel in college and got way better gas mileage. I'm not sure how our modern fuel injection and sensors would react, but there is usually legislation in Congress that tries to make acetone a permanent fuel additive in gasoline. Acetone breaks the surface tension of the fuel (just like soap in water) and allows for it to be burned easier. My testing found that 4 ounces to every 10 gallons were about the upper limit of returns for my 1998 Toyota Tacoma 3.4L V6 with manual transmission. I'm sure the application would vary. You can buy it by the gallon at paint stores (100% pure acetone), a funnel, and a measuring flask is all you need. And maybe a rag. My Tacoma had a 17.5 gallon tank. So I would keep 7 ounce capped vials of the stuff behind my seat. I would run her empty, add a vial, and fill her up.