What Causes Water Dripping Under a BMW?

[GrahamFitz]

There are two common scenarios for water dripping under the car chassis: drainage from the air conditioning system and water dripping from the muffler and exhaust pipe at the rear of the vehicle. Below is a detailed explanation: 1. Air conditioning system drainage: During summer, when outdoor temperatures are high and the air-conditioned car interior is cool, a temperature difference forms, leading to water condensation dripping from the chassis. The low-pressure pipes of the car's air conditioning system are not wrapped with thermal insulation foam, making the pipe surfaces prone to condensing moisture from the air. Water droplets then gather and drip from the lowest point of the pipes. 2. Muffler and exhaust pipe dripping at the rear of the car: This is also a normal phenomenon, typically observed in winter. When gasoline mixes with air in the cylinder and undergoes complete combustion in the combustion chamber, it primarily produces carbon dioxide and water. At high temperatures, water is discharged into the atmosphere as gaseous vapor. Since the muffler is located at the rear of the car where temperatures are relatively lower, the water vapor condenses into liquid water upon cooling.