I spray my engine down every couple months i use engine brite(do not use on hot engine It will flame up on headers/mani's)
I use pressure washer stand back a little unless im triing to hit a tough spot
i just bag the open cone havent had any issues except on my wagon it missed for a little bit till it dries

After you wash and rinse just let the engine dry or run it at ide for a few min to dry