I've never known Gunk to remove paint, but a pressure washer will always peel off any paint that's already loose.
Get the engine nice and warm, spray on your cleaner and let it sit (don't let it dry), then brush and/or rinse off. Hot water helps if you can get it, a lot of car washes have warm water on the soap setting.
I used Castrol Super Clean on the lower area of my engine and didn't lose any paint. The CSC will take some paints off, but usually just on poorly prepped rattle can jobs. CSC is my go to cleaner for tough grime, but you don't want it on glass or stuff like plastic chrome, clear plastic, etc., and don't let it dry. It's pretty strong at full strength, but can be diluted. It's awesome on tires, vinyl siding, aluminum, engine parts, fiberglas boats ... lots of stuff.
I use dishwashing liquid in hot water to wash the bike and it takes light grease off too.