[Blue Bowtie]

If the engine is cold, it is safe to use a hose. Try to avoid any direct spray at engine harness connectors, ignition components, and the alternator. Water won't really hurt them, but if water somhow gets past the seals, the eventual corrosion may cause connection problems. The alternator is relatively impervious to water, but the rear bearing in the alternator is not.

I use a hose with hot water, soap, and a stiff brush to clean stubborn spots. I've also used engine degreaser (basically kerosene) and other solvents to clean heavy accumulations of oily dirt from seepage and dust mixtures (what some people errantly call "grease").