Generally is just signifies some kind of engine trouble. If you watch
the smoking car, it will usually stop in the pits for repair within a
few laps. There is no danger of this causing trouble for any other
cars on the track.
--
Emory University Graduate School of Arts & Sciences
The IWCCCARS Project: Q & A Representative
Nascar Setups Page: http://www.racesimcentral.net/~ebusch/