I have noticed several different moments in the first Cars movie, that Sally or Mcqueen appear to be crying. Look closely at the lower portion of their windshields in the “Goodbye” scene, and also the final race scene when you see Sally smiling after Mcqueen helps the King.
Do you see it?!?!
I do see it and I know some others have to. Yes, they are crying. 
Awwwwww! I see it! 
Totally saw it. She also tears up a bit when she sees Lightning helping The King later. w
Well yeah, it would be emotional for them. Making the cars seem like they can get emotional and cry makes them seem more human and more relatable