White smoke is caused by either unburned fuel or coolant. On the common rail Cummins, white smoke is more characteristic of an injector problem.
If the exhaust smells almost like bug spray, it is unburned fuel. Injector and poor fuel problems can typically be cleared up by treating the truck with Diesel Extreme.
If the exhaust smells slightly sweet, it is coolant. This can be associated with a head gasket failure. This can also cause a mix of coolant and oil.
If it is smoking white all of the time and the exhaust smells almost like bug spray, feel free to contact one of our diesel experts.