I cover the Alternator, computer, distribitor & battery.
I also make sure my engine is cool when I do this,
and I am very careful not to spray too hard on any
oil seals. Cold water + Hot engine = possibly bad
news.
I wash my engine every morning after I take it out
4x4ing.
I got to a little place we have near by that has a
pressure washer. It gives out a spray that is not too
hard, the equivalent to what you get out of those
little spray things on your sink, but a lot wider, and
a bit harder (it does this when not pressing the
trigger).
Anyways, are you cleaing out grease of just dust
and debree? If grease, then use some sort of
degreaser and be EXTRA careful of the seals
If
you are leaking oil at all, pressure washing a seal could
be a bad thing.