Costco will install new gas pumps at its stores in Tennessee to save drivers money when fuel temperatures rise above 60 degrees.  Experts say retailers adjust for warm temperatures when they buy gas wholesale, but not when they sell to consumers.  That means you're buying fuel containing less energy because it expands when it gets hot.  Consumer advocates say drivers are getting overcharged as much as $2 billion a year.  The Los Angeles Times reports Costco is the only retailer so far to install new pumps in the wake of a consumer lawsuit against oil companies and gas stations.