Oven cleaner. I get mine from Ace Hardware. It'a $1.99 a can, on sale alot for $1.00. Quality Care is the brand. You can get a brand called Powerhouse at the Dollar Tree for $1.00 but it's not as good as the Ace stuff. Easy Off cost too much. $4.00 to $5.00 a can. It will remove some paint and the skin off your hands so wear gloves and try not to breath the stuff. Spray on and let set over night then hose off. The engine degreasers like Gunk that you get at the auto parts store leave behind an oily film.