White Smoke can be Coolant or atomized Fuel that did not burn. You might be able tell if it is Fuel by holding a clean Rag near the Exhaust Pipe and smelling the Rag to see if it smells like Fuel.

If the IP Timing is retarded/Late it will cause white smoke; I had this happen to me when I miss installed my Volvo Fuel Injection Pump. Making the timing right fixed it.

To a lesser extent worn Injector Nozzles can also cause it but it is more normal for the smoke to be gray.

Checking the Glow Plugs is easy.
Valve Adjustment may also help.

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84 300D, 82 Volvo 244Gl Diesel