Unexplained MPG Decline

[sully963]

2011 XLT current mileage 173,000
I purchased my 2011 five years ago with 90,000 miles on it. Ever since then my MPG consistently sat around 17 with my daily mix highway/in town driving. In the last month I’ve seen a decline in mpg to 15.8 with no change in driving patterns . Air filter is clean and sparks plugs have about 70k on them and tye MAF is clean. The weird thing about this is that it still runs just as strong as day one. I haven’t felt any change in throttle response or acceleration. No codes either and I have been through three different tanks of gas since I noticed the change in MPG. Any thoughts or has anyone else experienced an unexplained change like this? Is it normal to see MPGs decline with higher mileage?

 

[13o13]

Has your tire pressure changed? Hard tires roll easier.

 

[GlennSullivan]

Along the lines of rolling resistance. Get the vehicle up in the air and rotate the tires and wheels, feeling for resistance in the drivetrain. Brakes, bearings, differentials, etc.

Other thoughts, Cats, O2 sensors

 

[sully963]

Along the lines of rolling resistance. Get the vehicle up in the air and rotate the tires and wheels, feeling for resistance in the drivetrain. Brakes, bearings, differentials, etc.

Other thoughts, Cats, O2 sensors

Good idea. Thanks

 

[sully963]

Has your tire pressure changed? Hard tires roll easier.

PSI is good

 

[BigOleFordFan]

Well, a 1.2mpg decrease isn't that bad, considering the age/mileage, and I would only be concerned if it continues to drop further, which would warrant some further investigation....

A few months ago, my '011 with ~90k started dropping from it's normal ~17 mpg down to ~11-12, so I went looking for the cause.....

NOTES: I do ~95% highway driving with cruise control set to 65mph, no towing or bad terrain, with 93 gas & regular oil & filter changes, and tire balancing/rotations, and add a can of SeaFoam fuel system cleaner to every other tank of gas.

I checked the MAF first, which was a little dirty, so l cleaned it thoroughly, and ordered a new one a month or so later & installed it, since AFAIK, the one in there was the OEM one that came with the vehicle. Then I changed to a K&N high-performance air filter.

Just these 2 simple steps helped get me back into the 15-16mpg range, so that's where I am at today & am happy with it.

As long as it stays this way, I will not do anything else for the foreseeable future

 

[bman440440]

With 70K on the plugs that is what I would be inclined to change 1st. Just my 2c

 

[sully963]

Well, a 1.2mpg decrease isn't that bad, considering the age/mileage, and I would only be concerned if it continues to drop further, which would warrant some further investigation....

A few months ago, my '011 with ~90k started dropping from it's normal ~17 mpg down to ~11-12, so I went looking for the cause.....

NOTES: I do ~95% highway driving with cruise control set to 65mph, no towing or bad terrain, with 93 gas & regular oil & filter changes, and tire balancing/rotations, and add a can of SeaFoam fuel system cleaner to every other tank of gas.

I checked the MAF first, which was a little dirty, so l cleaned it thoroughly, and ordered a new one a month or so later & installed it, since AFAIK, the one in there was the OEM one that came with the vehicle. Then I changed to a K&N high-performance air filter.

Just these 2 simple steps helped get me back into the 15-16mpg range, so that's where I am at today & am happy with it.

As long as it stays this way, I will not do anything else for the foreseeable future

I’m still on the factory MAF sensor as far as I know. I clean it every other oil change but maybe I should replace it. Thanks for the suggestion

 

[sully963]

With 70K on the plugs that is what I would be inclined to change 1st. Just my 2c

Yeah I was hoping to go a little more on them but it might be something to consider. But at the same time like I said it runs great. Idles smooth and acceleration hasn’t changed at all so I’m not sure

 

[DieselMonk]

I wonder about the alcohol content in the fuel. More alcohol less MPG. Very plain and simple.

 

[DeafBringer]

Yeah I was hoping to go a little more on them but it might be something to consider. But at the same time like I said it runs great. Idles smooth and acceleration hasn’t changed at all so I’m not sure

They need to be changed every 60k. They are also prone to cracking/fracturing when they get old, reducing ability for a clean spark.

 

[max78]

70k on plugs is quite a bit, I would def change them, you will probable get better millage than before if that is the cause.

If that's not the cause, like other said check for rolling resistance.

 

[GlennSullivan]

I wonder about the alcohol content in the fuel. More alcohol less MPG. Very plain and simple.

That is an interesting thought, 2011s were Dual Fuel. ECU could be adjusting for alcohol content.

 

[rlhaberm]

2011 XLT current mileage 173,000
I purchased my 2011 five years ago with 90,000 miles on it. Ever since then my MPG consistently sat around 17 with my daily mix highway/in town driving. In the last month I’ve seen a decline in mpg to 15.8 with no change in driving patterns . Air filter is clean and sparks plugs have about 70k on them and tye MAF is clean. The weird thing about this is that it still runs just as strong as day one. I haven’t felt any change in throttle response or acceleration. No codes either and I have been through three different tanks of gas since I noticed the change in MPG. Any thoughts or has anyone else experienced an unexplained change like this? Is it normal to see MPGs decline with higher mileage?

MY 2017 did the same thing & dealers were no help. Just after it passed 100K miles, My mileage dropped from normal 17-18 to 13. I googled and found several folks cleaned or replaced the mass air sensor, so cleaned mine and it helped a little. On a whim one day I bought a bottle of Lucas Oil fuel treatment. I’ve never been a proponent of additives like this, but figured “what the heck”. Well, amazingly my MPG started to increase, so next fill-up I added another bottle, and it went back up in to the 17’s. I’ve been adding a bottle every third tank or so, and still getting nearly 18 MPG. I would suggest spend the 10 bucks or so and give that a try before you take it to a dealer or mechanic. Also, you can clean the MAS yourself if you want to give that a try, but I’d go with the fuel treatment first. Good luck!

 

[Gumbyalso]

I have an '11 XLT 4WD bought new, now with 300,000 on it. MPG is just slightly less than when it was new. The only "mod" is a K&N air filter. I change the plugs myself every 105,000 per the scheduled maintenance guide. The two times I've changed them at 105K and 210K they looked like I could have just gapped them and put them back in. This 5.4 3V still uses almost no oil. I use synthetic and change every 5K. I had the rocker arms and lifters replaced at 250,000 because they were making noise. Cam phaser is original. From what I read now I should have had it replaced along with the rocker arms and lifters but that's water under the bridge. Starting to hear the front wheel hubs now and some engine ticking but performance is still very good, especially for 300k miles. Hope to get a few more years out of it. Finally sold my 2000 Expy 5.4L 2V with 386,000 on it a few months ago. I put almost no money into it during the 25 years I owned it other than for an intake manifold to replace the cracked one.

 

[Limoguy25]

2011 XLT current mileage 173,000
I purchased my 2011 five years ago with 90,000 miles on it. Ever since then my MPG consistently sat around 17 with my daily mix highway/in town driving. In the last month I’ve seen a decline in mpg to 15.8 with no change in driving patterns . Air filter is clean and sparks plugs have about 70k on them and tye MAF is clean. The weird thing about this is that it still runs just as strong as day one. I haven’t felt any change in throttle response or acceleration. No codes either and I have been through three different tanks of gas since I noticed the change in MPG. Any thoughts or has anyone else experienced an unexplained change like this? Is it normal to see MPGs decline with higher mileage?

Check the actuators that engage/disengage the front axles. In 2wd with the engine on they should freewheel. That’s how I fixed a similar issue.

 

[sully963]

MY 2017 did the same thing & dealers were no help. Just after it passed 100K miles, My mileage dropped from normal 17-18 to 13. I googled and found several folks cleaned or replaced the mass air sensor, so cleaned mine and it helped a little. On a whim one day I bought a bottle of Lucas Oil fuel treatment. I’ve never been a proponent of additives like this, but figured “what the heck”. Well, amazingly my MPG started to increase, so next fill-up I added another bottle, and it went back up in to the 17’s. I’ve been adding a bottle every third tank or so, and still getting nearly 18 MPG. I would suggest spend the 10 bucks or so and give that a try before you take it to a dealer or mechanic. Also, you can clean the MAS yourself if you want to give that a try, but I’d go with the fuel treatment first. Good luck!

I’ve used lucas in other vehicles in the past with good results. I’ll give it a try next fill up

 

[sully963]

Check the actuators that engage/disengage the front axles. In 2wd with the engine on they should freewheel. That’s how I fixed a similar issue.

Thanks . I didn’t even think about that being a problem

 

[sully963]

I have an '11 XLT 4WD bought new, now with 300,000 on it. MPG is just slightly less than when it was new. The only "mod" is a K&N air filter. I change the plugs myself every 105,000 per the scheduled maintenance guide. The two times I've changed them at 105K and 210K they looked like I could have just gapped them and put them back in. This 5.4 3V still uses almost no oil. I use synthetic and change every 5K. I had the rocker arms and lifters replaced at 250,000 because they were making noise. Cam phaser is original. From what I read now I should have had it replaced along with the rocker arms and lifters but that's water under the bridge. Starting to hear the front wheel hubs now and some engine ticking but performance is still very good, especially for 300k miles. Hope to get a few more years out of it. Finally sold my 2000 Expy 5.4L 2V with 386,000 on it a few months ago. I put almost no money into it during the 25 years I owned it other than for an intake manifold to replace the cracked one.

Yeah it’s been a great vehicle so far. It rides super smooth and very little road noise on the highway. I’m hoping to get at least 250K out of mine.

 

[sully963]

Well, a 1.2mpg decrease isn't that bad, considering the age/mileage, and I would only be concerned if it continues to drop further, which would warrant some further investigation....

A few months ago, my '011 with ~90k started dropping from it's normal ~17 mpg down to ~11-12, so I went looking for the cause.....

NOTES: I do ~95% highway driving with cruise control set to 65mph, no towing or bad terrain, with 93 gas & regular oil & filter changes, and tire balancing/rotations, and add a can of SeaFoam fuel system cleaner to every other tank of gas.

I checked the MAF first, which was a little dirty, so l cleaned it thoroughly, and ordered a new one a month or so later & installed it, since AFAIK, the one in there was the OEM one that came with the vehicle. Then I changed to a K&N high-performance air filter.

Just these 2 simple steps helped get me back into the 15-16mpg range, so that's where I am at today & am happy with it.

As long as it stays this way, I will not do anything else for the foreseeable future

Did you buy the oem motorcraft MAF ?