Like the title says, i was wondering if bad o2 sensors would hurt my gas mileage. before i did my head gaskets there was coolant on one of my sensors and after i replaced the gaskets my gas mileage went from about 26 to about 20. and no i did not replace the sensors. thanks doods!

 

Big time. My car was getting very very bad gas mileage. It would take me a full a tank to get to work once a week. But with bad o2 sensors I was filling up every other day a whole tank. My car was idling at 1k. But since I replaced 02 sensors my gas mileage is back to the same. My car idles at 800 now. My car no longer has a misfire or miss at high speeds. 02 sensors can cause allot of problems. They are no joke. I didnt know that a sensor like that could have a big affect on my car.

 

yea it will cause bad gas mileage! what year is your car?...is it throwing a SES Light? im also wonderin if bad O2's will always throw a light

 

yeah mine threw all kinds of lights on also. My car is a 94 z28. Recently after a header install and cat removall. My 02 sensors went bad