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What do loose filler caps do?

  1. Increase fuel efficiency

  2. Waste fuel

  3. Improve car aerodynamics

  4. Reduce car's weight

The correct answer is: Waste fuel

Loose filler caps can lead to fuel evaporation and leaks, resulting in wasted fuel. This can also be potentially dangerous if the fuel leaks onto hot engine components and cause a fire. While properly closed filler caps may not directly increase fuel efficiency, it does prevent unnecessary fuel waste. Loose filler caps do not have any impact on car aerodynamics or weight.