* Fuel evaporation: This is the most immediate and significant consequence. Gasoline is volatile and will evaporate into the atmosphere. You'll lose fuel, leading to decreased fuel economy and potentially running out of gas sooner than expected.
* Evaporative emissions system (EVAP) trouble codes: Modern cars have an EVAP system designed to capture fuel vapors and prevent them from escaping into the atmosphere. Driving without a gas cap will cause this system to detect a large leak, triggering a check engine light and potentially setting diagnostic trouble codes (DTCs). This can impact your vehicle's emissions test.
* Reduced fuel efficiency: As mentioned, the direct loss of fuel due to evaporation significantly reduces fuel efficiency.
* Possible damage to the fuel system (in some cases): While less likely, in some extreme cases prolonged driving without a gas cap could lead to fuel system issues, though this is usually related to more serious fuel system leaks beyond just the lack of a cap.
* Foul smell: A strong gasoline smell will permeate the car and the surrounding area.
In short, don't drive without a gas cap. Replace it immediately.
