In a sauce pan, combine sugar, flour, 1/2 teaspoon salt, pineapple juice and eggs. Stir and cook over medium heat until thicekend. Remove from heat; add lemon juice and cool to room temperature.
Bring water to a boil, add oil and remaining salt. Cook pasta until al dente. Rinse under cold water and drain.
In a large bowl, combine the pasta, egg mixture, mandarin oranges, pineapple and whipped topping. Mix well and refrigerate overnight or until chilled. Before serving, add marshmallows and coconut.