White smoke on deceleration
Since you're on the road, try the following before starting the engine:
1. Check coolant level. Low coolant could be a number of things, Gasket, Sleeve, etc.
2. Cold Crank it with the key off and listen for a skip. This would be a good indication of compression failure in a cylinder such as a ring, valve, etc. You'll need a piece of wire to jump the solenoid on the starter - or do it the old fashioned way which I am not a fan of.
3. If the other two are negative, after you start it see if the exhaust smells very rich with fuel or a coolant odor (more so than normal for the fuel). This would indicate an injection or fuel delivery problem in general. And sometimes a gasket or O-Ring issue, rare but does sometimes occur.
A Diesel produces white smoke on "incomplete" combustion which could be caused by several things as well. Obstructed fuel delivery to the cylinder or cylinders, malfunctioning injector and so on. Or, just ****ty fuel.
Hopefully, its just the fuel. You could also introduce an additive which may correct or minimize the problem if it is. If you have any of these or an abnormally long cranking time to start, vibration at cold idle, I would be very leery of driving it any distance at all.



