To keep my engine looking like this I use the following
I've never used a jet wash in the engine bay and never would.
With respect chaps Gunk is as much use as a handbrake on a canoe.
This is the best and easiest to use engine cleaner I have found, and I've tried lots of products and methods.
I spray it directly onto a small sponge (yellow & green things girlies have in the kitchens) then just rub everything other than shiny metals.
That's it.
Best thing is that it is a water based product. Acid free.