I've used Rust-Oleum semi gloss black rattle cans on several engine bays and it holds up extremely well - for decades. I've also used Duplicolor with equal success. Both types are reasonably priced and locally available at Walmart and Advance Auto.

I never worried about curing or engine bay temperatures with either one and they don't flake off or peel. Don't overthink it.

Rustoleum on engine bay and Duplicor on engine.
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1950 Chevrolet 3100 (Ol' Roy)

1939 Packard Standard Eight Coupe (The Phantom) | 1956 Cadillac Coupe de Ville (The Bismarck) | 1964 Ford Galaxie 500 coupe |1966 Ford Mustang (Little Red) | 1969 Pontiac GTO (The Dishpit) I 1979 Ford F-100 | 1976 Ford F-150 (Big Red) | 1995 Ford F-150 (Newt)