DO NOT STEAM CLEAN YOUR ENGINE!!!!!
If you have a dirty engine or has a oil leak then get a cleaner and locally clean your engine then sprinkle water on it to wash it down, then using a high pressure air line dry the engine where you have cleaned.
If you are doing it for show purposes ie to make it look good then clean it part by part using a brush and engine cleaner to clean stubborn marks, then shower down before using a high pressure air line to dry the engine. To add a shine spray the entire engine using tyre Foam, this will clean any bits you have missed and leave a steak free shine to all rubber plastics and some metals.
If you experience any problems afterwards use ignition sealer its like WD40 spray all sensors connectors etc before using a high pressure line to dry any electrical sensors and components/connectors.
By the way the best advise is 'if it aint broke dont try to fix it!!!'