I just bought my first Mercedes (1988 560SL), but would like to know what kind of fuel mileage I should expect. My first 120 miles of mostly highway driving provided only 13 mpg. I just replaced the air filter, which still showed light through, but the car had been stored all winter with an empty tank. I filled it when I bought the car and added fuel conditioner, but should I expect the mileage to get better as I run it for a while?