Cleaning your engine compartment is fine. You can RINSE, but do NOT soak.

 

When I used to detail cars, we cleaned engines occasionally. We started the engines and sprayed degreaser with a squirt bottle anywere it was needed and rinsed with the pressure washer on low, trying to keep away from anything electrical, air intake, exhaust manifold, and especially the fan. Sometimes an engine would start idling rough but by the time we were done it usually was idling fine again.

 

I found a nice degreaser that won't eat paint.

Castrol Super Clean, it comes in a purple-colored spray bottle. Use this stuff for spot cleaning hard to reach areas. I thought it was pretty good at dissolving grease and dirt under the hood. I

I really liked it for cleaning the under side of my white hood, and the other greasy areas where my white paint was dirty.