-Hey there. My Neon's mileage has dropped fairly significantly lately. I was averaging 32-33 mpg going to work and back, about 65/35 highway-city driving, now it's dropped down to an average of 27 mpg. I have newer plugs in it along with air filter and plug wires. It runs totally smooth and no hesitation in town or on the highway. Does an O2 sensor cause this problem? I've never replaced one before so it's new territory for me. I want the mileage back up where it was, especially with vacation coming up in a few months. I loved seeing my mileage climb to 37 mpg even with the A/C on while heading South on I-77. Oh yeah, one more thing. No codes what-so-ever show up from doing the key dance.

L8R,
Matt

 

New O2 sensors have the possibility to up MPG if they are on the edge of being bad enough to throw a code. If they are still in good condition, a new one won't do anything.

 

-I just can't figure out the drop in MPGs. Like I said, the car runs smooth with no issues. Tires properly inflated, alignment done in December, and I usually try to keep the RPMs below 3k when shifting taking off from stops. Maybe goes a little higher when getting on the highway.

L8R,
Matt

 

Getting any of that awesome watered down gas?

 

-I doubt it. Like I said before, the car still runs smooth. Just the drop in MPGs. I usually stick with Speedway, Sheetz, or Sunoco gas, as I have for years. This is just irritating the crap outta me...

L8R,
Matt

 

How's the weather been? windy? rain? Snow?, Cold?, What's your idle warmup time each day? notice gas prices going up....any chance a neighbor has discovered your vehicle is easy to retreive gas from?

How long ago did you notice the change in fuel mileage?

You can grasp at straws assuming a bad 02 sensor, but what do you do after you spent the $ and time changing it and the problem didn't fix itself, then what? Have you used proper diagnostic methods to determine if the Oxygen sensor is functioning properly?

 

-I park in my garage when I'm at home, and I can see the gauge dropping a lot quicker than before while driving. I started noticing the fuel drop probably about a month or so ago before I did the timing belt and stuff. I also changed the thermostat, hoses, and coolant while I was at it.

L8R,
Matt