What does glass oil film mean?

[AlexMarie]

Oil film refers to a layer of grease and impurities adhered to the car window glass. There are several causes of automotive glass oil film formation: First, vehicle exhaust - exhaust emissions contain various pollutants from incomplete combustion. Frequent traffic congestion in urban areas, especially when driving behind trucks, inevitably leads to these substances adhering to the glass and forming an oil film. Second, oil smoke pollution - if frequently parked near restaurant chimneys, accumulated grease and dirt will gradually form thick oil stains if left untreated. Additionally, insect remains and bird droppings, which are highly corrosive, can harden on the glass if not cleaned, affecting transparency and potentially developing into oil films. Lastly, tree resin - vehicles regularly parked under trees may accumulate sap and fruit residues.