If you take the radiator cap off when it's cold, start the engine up, and keep and eye on the coolant, won't bubbles start to come up if there is air being leaked into the cooling system (ie either leaky hoses or leaky head gasket)? Or am I off my nut.
Also, I thought oil burning smoke had a slight blue tinge to it as well?
Thirdly, does it blow white smoke in the mid arvo, or is a morning/evening thing?