Car windshields end up with a lot of grime and oils that are hard to get off even when using windshield wiper fluid. A good trick I use to get off built up grime and oil is cola. Just pour a can of Coke or Pepsi on the windshield and scrub away. It does a great job of cleaning your windshield. Just be sure to do this when you are washing your car. Cause after you clean off the windshield you'll want to completely rinse all of the soda off since it will turn into a sticky mess itself if it dries on the car.