Many plug-in hybrid electric vehicle (PHEV) drivers experience the unusual occurrence of a fuel smell, even after half an hour of driving. This phenomenon may leave them puzzled, wondering if the smell is due to unclean hands touching the fuel cap or the electrical components in the vehicle. However, the true reasons behind this subtle yet noticeable aroma are rooted in the vehicle’s technology and design.

Volkswagen has provided clarity on this issue, explaining that the smell is associated with a common occurrence in all vehicles equipped with internal combustion engines: fuel vapor. These gases are always present but are usually absorbed by the catalytic converter and burned by the engine. However, in PHEVs, where the electric motor can power the vehicle for extended periods, the internal combustion engine might not operate continuously. This can lead to a temporary increase in the visibility of these normally benign vapors.

Why Plug-in Hybrids Have a Gas-Tight Fuel Tank

Plug-in hybrid electric vehicles are designed with a gas-tight fuel tank to prevent fuel vapor from escaping into the environment. A sealed system like this can create a vacuum or pressure changes in the tank due to temperature fluctuations and vaporization. To manage these pressure variations, a vent is strategically placed within the system to allow safe release and intake of air. This vent, however, can sometimes emit a faint smell of fuel, which puzzles drivers.

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