So my gas milage has been dropping. I tried changing the plugs. The coils are fine. I use 91 or 93 octane gas (whichever is available). And I'm getting 100-120 miles on half a tank. The car factory tank size is 17.2 gallons. Any suggestions/ideas? Thanks.

 

City/highway what percentage? How do you drive your car, old lady or indy car?

Calculate you mileage. Fill up the tank. Hit reset on one of the trip mileage gauges. Drive till you at about 1/4 or less. Fill up again. Note how many gallons you put in. Do the math with how much you just put in and the miles you drove. Check that trip mileage.

 

I averaged 19-23mpg when I had mine in mostly city ~45-55mph driving.

 

I get on average 27mpg but it's mostly highway driving. One thing I did which drastically changed my gas mileage for the better was to check the black panels under the front bumper. Over the years mechanics had broken the little plastic clips that hold the panels up against the car. They were hanging down and creating quite a bit of drag while driving. I bought a bag of new clips off of amazon and then went under the hood and secured all the panels back in place. Since then I've been seeing almost a 5mpg increase over before.

Here is the link for the clips I purchased: https://goo.gl/b1wJJY