Even the Dawn website says that their product is not recommended for washing cars. Question and Tips Can I use Dawn to clean things other than dishes?
Dawn is so effective in cutting grease on dishes that over the years, consumers have used Dawn on other greasy messes around their homes, from cleaning kitchen messes like grease build up on the stove range hood to oily spots in the garage. Dawn is not recommended for window cleaning, car washing
, body wash or washing hair.
On a personal note, I do recommend Dawn for washing dishes. It's great!