What Causes Sudden Drop In Fuel Mileage?

I have a 2010 Ford Edge, and have gotten a consistent mileage in the city of
21-22mpg, and just recently began getting 18mpg. The outside temp dropped
from the 50s to 30s. The tires are inflated properly, the air filter
recently changed, fuel system cleaner used on a fillup, and ISOheet on
another fillup, but still no improvement. Could the temperature change
really be the cause or should I look for something else?

Hey There…..

Yes the temp change could be the cause, but would be pretty hard to prove.  The onboard computer is making fuel mixture changes as the temp changes.  Also make sure you are using the proper engine oil weight.  There is not much else you can do unless you have a check engine light that is coming on, then you should get the computer codes read and see what is happening.

Are you still under warranty, you might want to take it in and have them just take a look…….

Please share this with your friends,
Austin Davis


Follow up email


Thanks for the suggestions, i’m just past the 3/36 original warranty. no check-engine lights are on, so i’m not too worried, but it was just disconcerting that nothing except a change in temp (not even below freezing) could drop it 3-4mpg.

I would think that if something were wrong enough mechanically, some type of code would trigger a light as you said. the only change around the time this started was changing the air filter based on the dealers suggestion during the oilchange. the only filter for it at 2 different parts places in town was a cheap offbrand (as opposed to a fram), but it seems unlikely that could be the culprit either…


Good to hear from you again


Wow, so you have more than 36K miles on this vehicle….you dont stand still do you?

If I were you I would do two things

1. Change gasoline brands, and types.  You will see an increase in mileage with super unleaded over regular, and with your mileage you should be able to determine if the higher price is worth it to you in extra mileage and performance.  Also change brands..i.e. Shell to Valero

2. Replace the air filter with a Ford OEM (Motorcraft) one. The slightest restriction in air flow with your driving habits could really effect mileage. Cant say I have seen a cheap filter cause a drop in mileage, but since this seemed to have happened after an air filter change, it would be a cheap and fast test to swap it out.

Please share this with your friends,
Austin Davis

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