i have problem with touran 2006 when i start it comes white smoke and when it sit for hour it comes again i and it is spends to much oil

i understand that but the problem is that i do not loos any coolant from can, because if i have coolant leak i will loos coolant but none i already replaced some rings in injectors still nothing.i am cap asking mechanics they do not have any idea the only thing that they say to me replace the engine !!