I know I've brought this up before but I've been doing fine up until now. The Escape got decent mileage during the summer but something has changed. I was getting somewhere around 18-20 mpg driving to work daily, since the last week of May actually. But in September, that abruptly changed, I started getting anywhere from 15-18 (on the high end) and I can swear I haven't changed my driving habits since the summertime.

The only two things I think might be interfering with my gas mileage is the oil, which coincidentally I just changed back in May before I started getting better gas mileage and just changed again today OR the oxygen sensors, which might be the reason for my P0420 code that I've had since late July.

My question to you is, what is the most likely cause and what should I be looking for? What do YOU think is causing this poor mileage? What can I do to fix it (that is cost effective) or have I already done that?

 

If there is ethanol in your gasoline you will get considerably poorer gas mileage in colder temperatures, my experience anyway. Try switching to a premium gasoline and see if you notice a difference. I used to loose about 5MPG in the winter all the time unless I wanted to pay the extra for the premium..

 

At 60 cents more a gallon that doesn't really make financial sense to me. If mid-grade brought me up 3 mpg it might be worth my while, but even so.

 

It would at least let you know if that is your problem, if it improves with pure gasoline then you have your answer, doesn't mean you have to continue using it. You asked for a reason..
Are you letting it idle longer to warm it up on cold mornings?

 

I'm having someone take a look on Tuesday night, at my O2 sensors and upper cats but maybe at the end of the week I'll fill the tank with mid-grade (89).

Meanwhile, I do not let it idle longer on cold mornings, I just drive it and wait for the engine to warm up before turning the heat up (it's always on low). I have noticed the engine seems to rev up a bit upon starting. Once in a while it will stall out after revving I think somewhere between 1000-2000. Makes me think it's not getting the right amount of fuel/oxyen, but I'm not a mechanic so I could be wrong.

 

Maybe check you air filter to see if there is a restriction there. Up here mid range still has 5% ethanol, not sure if it's the same in your area. I think your service engine light would be on if the O2 sensors were a problem. I'm not a mechanic either. Tire pressure is another thing to check

 

Engine light is on, code is P0420, which I've been told could be a myriad of problems.

Taking the info from OBD-codes.com

A code P0420 may mean that one or more of the following has happened:
-Leaded fuel was used where unleaded was called for (unlikely)
-A damaged or failed oxygen / O2 sensor
-Downstream oxygen sensor (HO2S) wiring damaged or connected improperly
-The engine coolant temperature sensor is not working properly
-Damaged or leaking exhaust manifold / catalytic converter / muffler / exhaust pipe
-Failed or underperforming catalytic converter (likely)
-Retarded spark timing
-The oxygen sensors in front and behind the converter are reporting too similar of readings
-Leaking fuel injector or high fuel pressure
-Cylinder misfire
-Oil contamination

It doesn't seem to be a coolant sensor issue as the gauge has always appeared to be at the accurate levels. I'm not sure where you can find leaded fuel these days, so that can obviously be ruled out. I'm not noticing any leaks or anything that would indicate spark plug or cylinder issues, and the oil looks fine.

Edit: Air filter was replaced a few months ago with a K&N reusable filter and I just filled up my tires last week to 34 psi.