I have a 2006 mercury mountaineer awd v8 which up until a few weeks ago would be able to get 22 mpg highway. I have noticed that recently it has been around 17 mpg at the same speed. Could all of this be blamed on winter gas blend, or is there more to my problem?

 

I could be wrong on this, but I don't think there is much of a winter gas blend any longer. Almost all gasoline is oxygenated regardless of season, which was the biggest hit to fuel mileage. In the old days, winter gas just meant something with a lower vapor pressure, but I don't think that affected energy content of the fuel noticeably (in my experience). Then the oxygenated stuff appeared, to help cut down on unburned hydrocarbons while your carbureted engine was still running on the choke, but that became political and now it's here to stay even though there's no benefit (and in fact, creates higher emissions of formaldehydes if the oxygenate is alcohol, but that's another story). I never noticed an appreciable decrease in the winter until the oxygenated stuff appeared for good in 2008, but my Fords are old by most people's standards.

I only noticed a 10% decrease with the oxygenated fuel on my older vehicles. My 2007 Toyota wasn't affected nearly as much. Your '06 should have a wide band O2 sensor, which is better able to deal with oxygenated fuel and your mileage hit seems too high to me at over 20%.

If you've been experiencing unusually cold weather and warm up your Explorer for 10 minutes before driving, that might explain some of it. Also, it will run rich longer until warm and that will affect mileage.

If it were just due to the winter season, you should have noticed this last year at about the same time. But, if you don't keep records, maybe not. I think your mileage decrease deserves a little investigation.

 

This is my first year owning this vehicle. Im up in rochester ny and it is really cold. So I knew I would lose some mileage but not as much as this. Also it seems like I can hear the engine more than I used to, almost like it got louder.

 

Another factor is that very cold weather decreases your tire pressure....more rolling resistance, less mileage.

 

I have kept my tire pressure the same all year, I run it at 35 in all 4 tires and check every 2 weeks

 

Well, if your tires are properly inflated and your driving habits haven't changed too much then you can start looking at your tune.

How many miles does your '06 have? A few places to check...You can check and clean/replace air filter, 02 sensors could be slowly dying out, mass air sensor could be needing a cleaning...numerous things to check.

My gas mileage does decrease in the winter a little. (as earlier mentioned) Mostly, because I will let it warm up a little longer than normal, run the heater all the time (which is just like turning on AC because Ford wants to keep the AC compressor lubed year round) and I don't check my tire pressure as much as you do.

Going from 22 down to 17 mpg is quite a jump..keep looking

Not sure if that will help but I gave it a shot. Good luck..

 

If you have noticed a mpg decrease lately without any explanation or driveability problems with you mountaineer you aren't the only one. This happened to me too.

I have a 2004 Aviator AWD and I noticed the same thing, but my mpg dropped down to 17 from 19. I think the main thing I found to bring the mileage back up was to find a place that sells ethanol free fuel. It does cost more, but it runs better, starts cold better and saves your injectors too. I used to work at Ford when the fuel was better and we used to get a lot of low mpg complaints from mostly truck owners :-)
This was in Colorado Springs, CO and we'd still hang the 1 gallon container on the vehicle and test the mileage and surprisingly the 5.8L F-150 pickups would get at least 17 mpg on the highway at speeds of 55 - 60 mph. It was usually because they were using cheap gas and have a heavy foot on the gas pedal.

One other thing I found with my Aviator causing a problem was a dragging brake caliper on the left rear--that made a 1.5 mpg difference. I also run all Amsoil lubricants which is hands down the best way to sustain the life of your vehicle and get the best mileage. I was in the Air Force for 25 years and found out the base stock components in Amsoil are the same ones for the jet engine oil (7808) we use in the F-15 fighter aircraft. I got into the jet engine technical manuals and verified this.
If you don't have any leaks or mechanical problems and plan on keeping your SUV I would use Amsoil products in it. Plus the engine oil is warrantied and you can run it 12,000 miles between oil changes as long as you are using the Amsoil filter. If you spend another $175.00 or so for the external oil filter kit you can run the engine oil 25,000 between changes, but I stick to the standard spin on filter and go 10,000 -11,000 miles between changes. This saves money too. I would not try and run Mobil 1, Castrol or Royal Purple 10,000 miles. Their additives and detergents burn off--that's what the result was on testing all the oils against each other.

Let us know if you found anything wrong causing your mileage to drop off, but do the easy things first like switching fuel and checking for things like I mentioned.