2015 Rondo - huge cloud of smoke

After a nice long leisurely August Sunday drive, I stepped-on-it to
pass a tractor - it hesitated for a second - then accelerated ok - but
I looked behind to see a huge cloud of <blue> smoke behind me ! 
2015 Rondo with 145 k km ; owned since new and maintained well ; 
no previous problems. No obvious performance issues ; no warning
lights. Any ideas or suggestions are appreciated. It's been a great
car for  7 years - except for this worrisome event.
 ps :  my sister-in-law has experienced similar with her Elantra.
   John T.