White smoke would make me think there might be a head gasket leak, with coolant getting into one of the combustion chambers. It could also be brake fluid, ATF, or another type oil getting into the intake somehow - Odd Stuff Happens.
If you do nothing else, keep a sharp eye on all the fluid levels AND their condition every day or two - radiator coolant, crankcase oil, ATF, power steering, brake fluid. If one is mixing with another, you may be able to spot it before it gets bad - harmful levels of coolant in the engine oil will make it get milky white, but by that point it may be too late.
Find a local heavy truck repair facility that deals with diesel engine repairs daily, and have them check it over - they will be more experienced at finding all the failure points. Your local Ford dealer probably has a mechanic or two specially trained to work on diesel engines, but unless it's a very large dealership he probably doesn't do it all day, every day.
If it's been a while since your last oil change, you might get a laboratory oil analysis done. The analysis can pick up coolant in the oil and some other nasty problems before the damage to the engine bearings is terminal.
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