i have found that useing degreasers can leave that white residue, but if you clean your engine bay before you wash your car that its good to spray wd40 around the entire bay. Stay away from alternator and avoid spraying in areas with electronics that may puddle. after you spray the engine area and cooling hoses just clean off excess with a rag. The wd40 leaves a nice shine and also protects plastics and rubber,"helps to keep them moist"