I find when I hav done the BIG clean, geting all the dirt/oil/road grime off as good as possible before I used a engine degreaser(which is mostly keosene).
I also try to keep it clean on a regular bases, so it doesnt build up, which will require some Elbow grease!
I use old tooth brushes for tight spots abd old rags to soak up crud and cleaners. Just my
Oh ya, Like Dan said some newr cars dont like to get wet under the hood.