I drive a very short distance to work every day (1.5 miles each way) and may drive 10-15 miles on the weekends. A tank of gas lasts me about 6 weeks. I know that driving short distances isn't good for the engine or exhaust system. What can I do to help keep my car in good condition under these short commutes? Should I only put small quantities of gas in my tank to help keep it fresh? Should I use a higer octane gas? Should I take it on the Interstate and run 20 miles of so once a week?

Thank you for your help.