Q: Engine coolant temperature on high and no heat inside

The engine temperature gauge was showing high.And there was no heat inside after heat is put on.I took it to a local mechanic.He told the heater core may be clogged.He flushed it.There was still no heat.Then,my friend checked the radiator,reservoir coolant level, and it was low.We topped it up.After a drive we checked the hose going back to the radiator.When we pressed it,we couldn't find enough pressure in the hose.My friend suggested that there may be air inside the coolant system.Well after a few hot and cold cycles,the hose was having pressure and we were getting slight heat.But the engine temp is still high.It gets to even beyond the red mark and when idling during a ride it gets below the red mark but beyond the half way mark. Yesterday I drove the vehicle for almost two hours ie I haven't stopped the engine.Finally,I was getting real heat inside with engine temp still high.After 3 hrs of cooling I drove again.heat is again low inside and engine temp on high.This is where I stand

My car has 160000 miles.
My car has an automatic transmission.