I dont know if this has been post before but everyone needs to watch this video! Its kind of long so scan through it. The guy cleans an extremely sludged up engine by pouring 1/2 gal of all purpose cleaner/degreaser into the engine with a qt of oil....Money shots start at the 9:00 minute and 16:00 minute mark
https://www.youtube.com/watch?v=acnAn-elvQE&t=1233s