Remember that nothing has less rolling resistance than a worn out Low Rolling Resistance tire. So even if you replaced your tires with a new set of OEM Enasaves, you would still notice a slight reduction in your fuel mileage.
Originally Posted by Spadesheart
You didn't mention what tires you are using. If you bought some off-brand tires that aren't Low Rolling Resistance, that could make a significant difference.
I know this sounds crazy...but you aren't driving around with your automatic climate control on all the time, right?
If there is something wrong with your car (like a bad coolant or air temperature sensor), this could have a significant impact on fuel mileage. There is a reading in the car's computer called "Fuel Trim." It's basically a reading that indicates if the computer is being directed to use more (or less) fuel than usual. You can read more about it here:
Fuel Trim as a Diagnostic Tool
A good tech would have looked at your fuel trim. A tech who's only getting paid 30 minutes of warranty time to look at your car may have just looked for error codes.
View my fuel log 2015 Mirage ES 1.2 manual: 51.4 mpg (US) ... 21.9 km/L ... 4.6 L/100 km ... 61.8 mpg (Imp)