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I own a 2003 Ford F150, Crew Cab, 2x4, 68K miles. For the first 5 years, I got 15 - 15.5 mpg consistently. In the last year, the mileage has dropped off to 13- 13.2. Everything has remained the same- oil changes, tire pressure, gasoline, same city/highway driving. Is there anyone who could identify why a vehicle suddenly drops 2 mpg in fuel effeciency? I’ve already been warned about the lack of benefit from fuel additives/snake oils, etc. Thanks!

E10 is probably the reason for the mileage decrease. Does the gasoline in your area contain 10% ethanol? If so, it could be the reason for the reduction in mileage.

The mileage of both my vehicles dropped about 10% as soon as E10 became standard in my area. If I can find a station selling ethanol-free gas my mileage immediately returns to “normal” within one or two tankfuls, but there are very few such stations near me, so most of the time I’m stuck using E10.

The advice you received about additives is correct. They are a waste of money and will not improve your mileage.

It’s possible there’s a mechanical or electrical problem contributing to the mileage reduction, but even if that’s true additives won’t help.

Thank you, you are the second person to include the E10 as a possible root cause.

Do you suspect it would be worth a trip to the dealer for a once over/tune up; or are they only going to charge me a ridiculous bundle of money to do nothing. This truck has not been in the shop since 800 miles- very very dependable. I admit, I did not complete any of the recommended 36K mile check ups, etc. I do it all myself or locally; but not at scheduled mileage.

Are you only noticing it during the cold weather? Cold weather riches up the mixture. General wearing of “tune-up” parts could also contribute.

Are there any other symptoms: drivability, feel of a drag? Got extra weight on board; carrying your mother-in-law in the bed?

I would suggest you bring all maintenance up to date according to the schedule that came with the truck. It may need something like new spark plugs, or it may not, but check the schedule to be sure.

I don’t take my vehicles to the dealer, either, but I make sure the recommended maintenance is done, either in my garage or by an independent mechanic.

There’s no such thing as a “tune up” any more. The computer adjusts the timing and fuel mixture as you drive to suit conditions.

As I said, the mileage on both of my vehicles dropped 10% when E10 became standard in my area, even though nothing else changed.

Not to overlook the obvious, air and gas filters are in good shape? Any other things like plugs, wires, etc. that have been taken care of. Are there any other symptoms? poor acceleration, longer cranking to start, Parking brake trouble etc.

With regards to cold weather, no, this began last summer. Additionally, I tow a horse trailer several times a year is all, and I haven’t towed anywhere far enough to get gas mileage during towing since this started. Usually, mileage was 12-13 when towing. I’ll be interested to see if it goes down to 10 mpg. One thought I had was that when I tow without overdrive, mileage is horrible; but it is supposed to save the transmission. I’ll ensure that the overdrive is back on, although it defaults to “on” each time I start up. Filters are all up to date, but I’ve never had spark plugs checked. No noticable drag with acceleration, nothing extra in the truck bed. Could be that none of my friends check gas mileage, so they don’t realize that theirs may have gone down as well, if we went to E10.
Great comment about Tune ups, I had no idea! I’ll take the truck to the local trustworthy mechanic to check plugs, and filters just in case.

Different tires or pressures. Check the spark plugs. Try getting your computer codes read. Some OBD II readers can warn you about emissions control systems that aren’t up to par. A worn out fuel injector can cause a drop in fuel efficiency.

As a follow-up to pdv’s post–Did the OP purchase new tires for this truck just prior to the drop in gas mileage?

Even though the inflation pressures may be correct, the fact remains that the rolling resistance of tires does vary from one brand to another. Car and truck manufacturers tend to use tires with very low rolling resistance, in order to get that last little boost to gas mileage on the vehicles that they sell. Then, when those tires are replaced a few years later, the new tires frequently have a higher rolling resistance, thus leading to a drop in gas mileage.

Everything is a trade-off. New tires may have better traction, or better resistance to hydroplaning, or may even ride more smoothly, but in order to gain those advantages, the tire manufacturer may have had to compromise on rolling resistance.