no no no dont do it its not worth the risk, it does way more harm than good, it may be ok to start with but i know from experience that ull end up having loads of hard to find electrical gremlins due to water ingress, beside and oily engine stops it rusting lol! if u must have a shiny engine use some sort of degreaser and do it by hand otherwise just leave the bonnet shut!
Get some of that aerosol Jizer/water soluble degreaser, nick the brush for doing the dishes out of the kitchen and get scrubbing. Give it a rinse off with a hose, just be careful where you get the water.
I clean my engine bay all the time and i have never had any problems so far.
I only please one person per day. Today is not your day, tomorrow isn't looking good either.
Just use degreeser and a hose but wait for a sunny day and warm the engine first. I used to use a paint brush to work the degreeser in. Do it a few times over the course of a month