This was my grandmother's favorite cake! Mandarin Orange Pineapple Cake

1 box Duncan Hines Butter Cake mix
1/2 cup Wesson oil
1 11- ounce can mandarin oranges
1/2 cup sugar
4 eggs
Icing
1 12 ounce tub of Cool Whip
small instant vanilla pudding mix
1 16 oz. can crushed pineapple
Preheat oven to 350 degrees.