2.2 petrel problem


Hi lads my name is Matt I drive a vectra 2.2 petrol 54plate 80k.
Iv got a couple of issues I'm hoping you can help .
When starting the car up white smoke comes out if you rev it hard it turns blue white .
There is no oil in the header tank.
When I look at the oil filler cap it looks like water drops on the under side.
Also car was left running for over an hour the temp gauge was on 0 but there SaaS hot air coming threw the vents.
Can anyone help much appreciated