Preheat oven to 350 degrees. Grease and dust with flour two 9" round cake pans. Make cake mix according to directions, using pineapple juice instead of water and add the 1/3 cup crushed and drained pineapple. Bake for 30 minutes. Remove from oven and turn out on cake racks to cool completely.
Mix instant vanilla pudding mix with the 12 0z. can of crushed pineapple(DO NOT DRAIN). Fold in the thawed Cool Whip. Frost cake and chill for at least 3 hours.