Oven cleaner with lye. The ones without do not work as well. Although, I would try sanding it with 400 first.
On my grill I repaired the back side of several cracks with body panel adhesive (incredibly strong stuff, but not brittle like epoxy) and in one small place I embedded a piece of sheet metal into the adhesive for strength. You can then fix the front of the cracks with filler; sand smooth and prime with a high build , catalyzed poly primer. (Catalyzed primer is thick, easy to sand, & will prevent any incompatibility issues b/t the original paint, and whatever you top coat it with) Wet sand with 400, then 600. Then paint. Btw, this is a 71 Challenger grill, painted with Hot Rod Flatz. It’s a urethane paint, very tough. After eight years it still looks great.
Hot Rod Black - Hot Rod Flatz Flat Matte Satin Urethane Auto Paint - Paint Quart Only - Professional Low Sheen Automotive, Car Truck Coating, 4:1 Mix Ratio
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