I spray my engine bay with water, then spray straight simple green and let it soak for a few minutes. Then I spray it again. I've never had problems with it, and Scott Settlemire's signature is still crisp and clear.

 

Superclean has done that to my engine bay. I think that the harsh cleaners eat away at the paint after time. Plus I think the paint in the engine bay has no clear coat on it or it is a mat finish paint.