2001 Geo Metro mileage drop from 52 mpg to 38 mpg, why?

[Modes]

My Geo Metro 2001 has 113K miles on it. The mileage has dropped from 52 mpg to 38 mpg. My mechanic has replaced the oxygen sensor three times. I detect no smell from a clogged catalytic convertor, nor do I have any performance problems. Can anyone suggest any other place to look to troubleshoot?

[geozukigti]

Considering a 2001 metro is only rated for 34mpg highway, I think 38mpg is a sweet deal. You may have been mistaken for it getting 52mpg. It's an MPFI 16v motor, there's no possible way it could get 52mpg unless it was a hybrid, or rolling downhill in neutral. Also, assuming you're up in the north here, heater blower motors use a lot of electricity. They can have a signifigant effect on gas mileage.