I use a cleaner from P21s to do a deep clean once a year. I wipe down the engine bay every time I was the car. Easy upkeep once the initial cleaning is done.
With as much water that enters the engine bay during hard rain and interstate driving, I don't see how a low pressure 'rain' setting could hurt anything. I do ensure my engine is warm and then drive it for a while after the deep cleaning.

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'03 Black BMW E53 3.0i 110,000+ miles
'03 Black Mercedes-Benz W211 125,000+ miles
'13 White Mercedes-Benz W2o4 New