Wash the car thoroughly with plenty of water and a good quality car shampoo, then use a clay bar such as the Meguiars Quick Clay Detailing System. It comes with the clay and a spray bottle of lubricating fluid. Simple to use and very effective in removing tree sap, overspray and industrial fallout crap. Be gentle with it, folding the dirty side in regularly and keep the clay well lubricated. Use little pressure and work in small areas across the car. The clay will lift off all the surface contaminants from the paint and leave it very smooth. Then clean, polish and wax the car immediately to ensure it is protected for the winter and DON'T park under trees again !
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