1999 Subaru Legacy outback over heating problem.

I have a 1999 Subaru Legacy outback that keeps
over heating. I flushed the radiator fluid twice with
distilled water and put in the radiator/coolant fluid,
changed the thermostat, and we changed the water
pump last summer. There isn’t smoke coming from
the end of the car and there isn’t white cottage
looking from the oil cap and we just changed the oil
and it didn’t look nothing but just old dark oil. When
I drive it doesn’t shake and it doesn’t have a weird
noise when I drive it. Before I drive it I check the
coolant and it’s at the regular full level mark but
when I’m driving and it over heats the coolant is all
the way at the top passing the full line.