If your vehicle is showing thick white smoke pouring from the exhaust, here are the most likely causes and the parts you'll need to fix each one.
The gasket sealing the engine block and cylinder head has failed, allowing engine coolant to leak into the combustion chamber and vaporize into thick white steam.
On engines where coolant routes through the intake manifold, a failed gasket can allow coolant to be sucked directly into the engine's intake runners and burned.
If head work was recently done, failing to properly torque the cylinder head bolts or clean the mating surfaces will cause the new gasket to leak coolant immediately.
On turbocharged vehicles, internal seals can fail, allowing the coolant that cools the turbo center cartridge to leak directly into the hot exhaust tract.
Severe engine overheating can physically crack the metal of the cylinder head or engine block, creating a permanent path for coolant to flood the cylinders.