bmw 523?

I inoticed the oil was getting a little low,topped it up wth a multigrade,a few miles down the road was playing with heater settings then noticed to my horror the needle was in the red and i was overheated,i looked out the rear view and a big cloud of smoke(blue).Eversince the car now overheats,have topped up oil n water,but she just overheats really quickly,no signs of head damage,oil in water etc.also oil service warning light comes on intermittantly.