Hi all, I'm new here but have done a fair bit of reading. Hoping for your input on this as I try to figure out what the problem is with my car. To sum it up my last 5 tanks have gone something like this 48 mpg, 38 mpg(got me thinking wtf), 42 mpg, 36 mpg, 49 mpg, and now 27 mpg. There are almost zero variables in weather, driving habits, tire pressure, etc. The only things I can think of are the 12 volt has died a few times b/c I left a light on. My key fab light flashes at me on the dash on random occasions. And the gas tank gauge is crazy off sometimes and spot on the other half. The mileage gauge in the car has been reading below 40 mpg on all of the above tanks. - Have you read This Thead Yet? Yes - What fuel economy are you getting and how are you determining fuel economy? (trip computer or manual calculations) Using manual calculations. Miles traveled divided by number of gallons pumped. - What fuel economy are you expecting and why? 48. I averaged that for 20,000 miles on this car. - What are the approximate outside air temps? Lately around 55-70 degrees. - How long are your trips? Varied but on some all commute tanks(under 10 mile trips) I've averaged 48 mpg and on some of the same style it's been 36.(and now 27). Same bizarreness on 100% highway miles tanks. - How much of it is city vs. highway? Roughly what's the average speed in overall and and of each segment? Is there a lot of stop and go driving? See above. I don't go crazy fast. Not a huge amount of stop and go even in the city driving. On the highway it's between 65-75. As mentioned my driving pattern is the same and never had a problem previously. I always averaged between 44-50 depending on these types of conditions. - What region/state are you in? (if you haven't set your location in your profile) Arkansas - What's the terrain like of your drives? (e.g. flat, gentle hills, steep hills, etc.) Half the state is flat and half hilly. Just depends. On some hilly highway trips I've gotten 52 mpg. And when this weirdness started I've gotten 36 going on flat interstate the whole way. - Is your oil overfilled? (i.e. above the full mark on the dipstick) No. How old is your 12v battery? What is the voltage reading of your 12v battery after sitting over night? (Method Here) I guess it's the original one. I haven't checked the voltage reading. Still trying to figure out how that would affect mileage. Wanted to get you all's opinion first before I take it in(not sure how to check the voltage). Have you had your alignment checked? Any pulling or abnormal tire wear? It's fine currently. - Are you using the factory tires and wheels? If not, please indicate tire make, model and size (e.g. Goodyear Assurance Fuel Max 185/65R15). They are Coopers. I need to run out and check the brand(dark here right now). They are the same size as the factory ones I believe. - What are your tire pressures? 35 all around. - Make, model, year, engine and transmission of previous car? (e.g. 08 Honda Civic Si 2.0L 4 cylinder, manual transmission) What did you actually get on the same trips/commute? (Please give us actual numbers, not EPA ratings.) I drove an 8 cylinder GMC Sierra 1500 truck which I still have. I got about 15-18 mpg on it. - How are you trying to drive (e.g. trying to stay in electric only?) and how hard are you braking? I'm not braking hard that I know of. I slow down using the 'b' button and try to conserve momentum. - Are you "warming up" the ICE (internal combustion engine) by letting it idle after powering on? Sometimes. - Are you driving using D or B mode? D - HVAC settings? Are you using the heater, AC, auto mode, etc.? If using auto, what temp is it set to? Haven't used the a/c or the heater in a while. - If reporting a mileage drop, did anything significant change on your car (e.g. accident, hit a curb or big pothole throwing off alignment, oil change/other maintenance/repairs, changed tires or wheels, etc.) or your commute? As mentioned the 12 volt going dead a few times is the only thing that has been weird. That and the gas gauges being way off. One time it signaled low fuel and I put 4 gallons in it and got 48 mpg. Then the next time it signaled low fuel, I almost didn't believe it. It was accurate this time and took almost 10 gallons.(and awful mpg). Thanks in advance for the help!