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Q: I started the engine and a big puff of blue smoke appeared. It only happened once. on 2007 Mercedes-Benz SLK280

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what would cause a big puff of blue smoke when starting the engine after sitting over night, it only happened once.!!
(1) Answer
Usually this is a sign of the failed valve stem seals. Some oil sweeps through the seals and burns in the combustion chamber at the next start.

Zee