I have a 2004 Honda Element with 152k. If I use the heater, the air that comes out smells like gasoline. As soon as I select circulation mode, the problem immediately stops. Any thoughts?
You have a gas leak under the hood. Stop driving the car and get it to a shop - now. Its possible that it is just an evaporation system leak rather than a liquid fuel leak. But there is no such thing as being safe when you smell gasoline.
When using fresh air mode, the air that comes through the vent system is drawn into the car from just behind the engine compartment. If you smell fuel–and you’re sure it’s fuel–there is a fuel leak somewhere that needs to be corrected immediately regardless of cost or convenience. Car fires are rare, but so are house fires, and you don’t want one.