Another Spanish Subjunctive question?

In the first example, both are correct. In the first one, you already own a specific car and you know exactly how much gasoline it consumes. In the second one, you want to buy some unspecified car, and you would hope that it would not consume much gas, so it is an unfulfilled objective and takes the subjunctive. In the third example, you are talking about the actual state of kidnappings in Latin America, which is known to be high, and thus an endemic problem. So you would use son, not sean.