This is exactly what I do..... and yes the engine must be cold or you will stain your intake mani or any other metal parts that are hot/warm.
On top of that I like to get a bucket of car wash soap with some wax additives (wash & was soaps) and actually scrub the engine bay with that as well after the simple green routine. I find it really helps in shinning everything up all nice.
Werd.... I probably do mine 2 or 3 times a year and as long as you don't let it get really bad it'll always look spotless.
Bookmarks