What could have happened?!

I’m the proud owner of a 2006 Ford Freestyle with about 46,000 miles on it. The car has a 19 gallon gas tank with mileage estimates of 18/25. When I first got the car I was getting about 350 miles per tank of gas, but by the end of the first year I was down to about 275 miles per tank. Not really being a car person, I thought this was pretty normal.

Well about two weeks ago I had a quarter of a tank of gas left and I went to fill up. After the gas had been pumped I started the car and the fuel gage went up to a quarter of a tank and stopped there, even though I had just put in about 14 gallons. I turned off the car and started it again and this time the needle dropped straight down to well below empty. I again turned the car off and back on and this time the needle dropped straight down again and the check engine light came on. Since it was the middle of the night, I didn’t really know what to do, so I drove home.

The next day, when I started the car, the fuel gage went up to full and the check engine light was no longer on. Everything seemed to be working alright so I didn’t think any more of it. Well since then I’ve filled up twice and I’ve noticed that I’m getting significantly better gas mileage. Three weeks ago I could barely get 275 miles out of a tank and for the past two fill-ups I’ve gotten nearly 400 miles! Nothing’s changed about where or how I drive. It just seems like magically I’m getting better gas mileage. Any ideas on what could have happened?

You are not determining fuel use properly. Fill your tank, record the odometer reading and drive. At the next fill-up, record the fuel added and the odometer reading. Subtract initial from final odometer reading. Divide the miles by gallons pumped. Repeat the process several times for the best accuracy.

Thanks for the fast reply! I probably didn’t explain myself properly, but that’s actually what I’m doing. Before this problem happened I was getting about 15 miles per gallon (calculated the way you described) which usually resulted in about 275 miles between fill-ups. But for the past two weeks I’ve been getting about 21 miles per gallon which has resulted in about 400 miles between fill-ups. Again, I haven’t changed where I’m driving, how I’m driving, or how often I’m driving, so I have no idea why I’m getting better mileage, and no idea what all the fuel gage stuff and engine light was about.

I too am unsure of your methodology. The only accurate way is to fill and divide the total gallons used (off of the pump readout) into the total miles traveled (off of the odometer) and to do so a number of times. Any other method is inaccurate.

I don’t quite get this out of your post. If I understand your post correctly you’re assuming how much gas in in a “fill up” rather than reading the volume off the pump meter.

Sorry for the confusion. I’m using the methodology that Beadsandbeads described, recording my odometer reading and the fuel added at the pump and then dividing to get a number of miles per gallon, exactly as described above. A few weeks ago that number was almost always a little less than 15 miles per gallon. Since I’ve got a 19 gallon tank, that means I’m averaging roughly 285 miles per 19 gallons (15 * 19 = 285) or 285 miles per tank. For the past two weeks I’ve been getting about 21 miles per gallon, again calculated as described above. At 21 miles per gallon with a 19 gallon tank, that means I’m now getting about 400 miles per tank.

When I say, “A tank of gas” I just mean 19 gallons worth of gas. So if I use 14 gallons, then fill up at a gas station, and then use 5 more gallons, that’s one tank of gas for me. It’s easier for me to think in terms of how far I can go on a full tank of gas than how far I can go on a gallon of gas. I didn’t realize that wasn’t socially acceptable to think that way.

So let me rephrase. Prior to the events of two weeks ago, I was getting slightly less than 15 miles per gallon, calculated as described above. For the past two weeks I’ve been getting 21 miles per gallon, calculated the same way. Any ideas why or what could have caused the problems with my fuel gage? Could there have been something clogging up the fuel tank?

In some parts of the country refiners are delivering “summer” gas now and that is very different in some locales than winter gas. Seems like a big jump, but the gas maybe a contributing factor.

Do you live in an area with seasonal changes?

Also, do you drive a lot of miles or is this all short trips? Unless you’re a high mileage driver a few weeks may not be sufficient to get a good mileage calculation.

You were doing good when you got away from how far you went per tankfull and expressed your mpg. The you lost it when you zeroed in to a problem with your gas gague. Ask the question “why has my mpg changed” or is the question “does anyone think I have a problem with my fuel sender/gague”