The bad thing about HOSING DOWN your engine is that you may be left with water spots all over the place if you do not followup with a wipe-down
more details at...Featured Articles >> Cleaning your enginehttps://www.celicahobby.com/ubbthreads/thread.f_57306_0_collapsed_5__1.html
Basically, the only thing that you should be concerned about getting water into under your Hood
is your Intake
Although the following items are already waterproof, you should check the tightness of the oil filler cap, the power steering filler cap, windshield washer fluid cap, oil dip stick, battery filler caps and all other engine compartment opening caps.
everything else should be fine... there really isn't much under your Hood
that isn't already water proof.