if teh smoke was oil the it would be blue

if black its fuel

if its white its water

as its coming out of the exhaust then its either turbo failure or head gasket

does it get hot,lose water, miss fire anytime?

if the turbo is watercooled block the water pipes both ends of the turbo, if its stops then the turbo is knackered, if it doesnt then head gasket

only tests you can do i think, bar a compression test aswell