I live near the coast so my engine has a coat of sand covering it.

I was wondering what are the dangers of using a high-pressure hose at one of those do-it-yourself car washes to clean the engine/engine compartment?

 

Beware of high pressure (or even low pressure) around the air filter and various electronics.
I've washed my engines for years (garden hose, 'thumb high pressure'.) Only negative consequences were in the '81 Fiat whose injectors grumbled a bit until dry.

 

as said, so long as you know where NOT to spray it can be done safely


I use steam myself .... you can buy a small steam cleaner for around $100 and steam cuts grease and oil very neatly. I bought it for the 79, but when needed it works just fine on the newer toys too


and if just 'sand' I use compressed air and a brush . . .

 

I'd sooner use the engine cleaning products available, a brush and low pressure water. Hopefully you are changing out your air filter more frequently than recommended by Mini.