A few years ago I read about washing car engines. I remember that there is a part that must be protected from water (the instructions were to cover it with plastic sheet and seal the edges of the plastic with tape), but I can't remember what that part is. Can anyone tell me?

Also, I would appreciate it if you gave me a general idea of where that part is located since I know some, but not a lot about car engines.

My car is a 1989 Madza 626 4dr.

All help will be greatly appreciated.