I recently moved in November, and have since been taking a different route to work. It is about the same distance, 25 miles, although very different roads. I used to drive winding, hilly, country roads for 25 miles at about 65mph. (I loved the twisties in this car!!) I used to get 24-26mpg. Now I drive 25 miles on the interstate with the cruise set at 70-75mph. Since the move, my mpg has gone down to 20-22mpg.

Now, I know I am going faster on the interstate, but not THAT much faster!! Also, I have taken several road trips in the car last year (none since the move) on the interstate at 70-75 and gotten nearly 27mpg out of it.

I have:
Changed the oil (Mobil1)
Checked the tire pressure
Changed the air filter just prior to the move
none of it made any difference

This just doesn't make sense to me that going from constantly on and off the gas, up and down hills, scorching around corners, (Tim the Tool Man Man Grunt "Arrgh Arrgh Arrrgh" thrown in ) to cruising down the road with the cruise control set. Seems to me it should have gone UP, not DOWN!!!

Any ideas???

 

Here are my ideas so far, but I'm still not satisfied, because I didn't see a drop like this in mpg last winter...

1. lower energy content of winter fuel blend
2. lower energy content of ethanol fuel blend
3. not super flat interstate, semi-hilly
4. my car's way of saying "I'm bored, give me the twisties back!!"

 

I have no idea... My Crown Vic is the same. I would get very good gas mileage one season, and bam I start dropping 2 mpg. I checked my logs and still cannot figure out why there is such a large drop in gas mileage. I've taken down readings since day 1.

Another theory is that there may be more wind on the highway during the winter which can increase the drag on your car. Ever try to jog/run with 10 mph winds blowing at your face? It's not as easy as jogging on a calm day because you are wasting energy trying to push through the winds.

I've managed to get 23 mpg with the 03 E-250 (5.4 2V V8, 3.73s) in the summer on long distance highway driving (70-75 mph, 300+ miles between fillups). I didn't do anything special other than just drive (no cruise control in the van).

 

Were you using the same type of fuel on both routes? Remember that when you are driving faster your gas mileage drops. Also keep in mind that we don't have the most aerodynamic cars so at higher speeds you will get more resistance.

 

Definitely true: your wind resistance is higher and your rpms are higher.

Also, winter mix fuel will decrease mpg, as will fuel with some ethanol in it (as theedge stated).

I always lose fuel economy in the winter due to this

 

I know crusing on the back roads at 50MPH and the freeways at 70MPH shows quite a difference in fuel mileage when you look at the trip computer in my car

Otherwise, keeping track of the mileage in all of my cars, I know that my fuel consumption tends to drop in the cold winter months, this is probably due to the fuel blends in addition to the fact that the cold air is much more dense.

Best suggestion, reset the mileage computer and try and drive both types of routes and see how you mileage reacts.

 

Winter fuel will decrease the fuel economy. I live where it's really cold we all know about the dammed winter fuel.

 

I would think winter blend does have something to do with it. Are you using anything in your tank such as heet? How many miles are on your car? Is it time for a bottle of injector cleaner?? Do you let it warm up in the morning more than a fe minutes?

 

I don't think you wanna be putiing any injector cleaner in the tank...there has been much written about additives and fouled plugs

 

I don't think I've ever seen that kinda mileage in my GT

 

You've gotta keep your foot out of the gas. Cruising at 60-65, I can get a solid 27-28 mpg.

 

I've experimented with that (driving at 60-65 mph using cruise control) on the highway during the winter and my best gas mileage was the average gas mileage I get in the summer driving 75-80 mph w/ the A/C on.

 

I haven't tried it with winter fuel yet. Those are summer ratings

 

Ive also read that it takes longer for the various fluids like differential oil, power steering fluid, oil, to warm up and thin out in colder weather which would contribute to a decrease in fuel economy.

 

That's right. This morning here it was -25, the power steering oil is so cold that for a few minutes you'd think that you dont have any.

 

Bad gas, clogged fuel filter, dirty air filter, etc...

Try cruising without using CC...

 

I have 36,000 miles on the car, no additives of any kind in the tank, I use any of about 3 different brands of gas...but the same 3 I used before. I do let it warm up at work on occasion for a few minutes, but even when I don't the mpg's just aren't there. I guess I am just confused why it would go down so much when I switched to interstate driving with CC on. I would think the twisties would have killed the mileage more, even at a little lower speed.

I don't know, I'll wait until it gets springtime to make a definite judgement on what is going on. Thanks for the help, I'll keep you guys updated!!

 

Change your fuel filter...

 

Wouldn't a clogged or dirty fuel filter affect max performance as well though? I have not noticed any power loss at WOT, and it seems that would be the time I would notice it most...when it's sucking fuel like crazy. Just thinking out loud here, I'll probably change it anyway just to see. How hard is it by the way??

 

I know when I was cruising home from Texas a while back the at steady cruise of 65 mph I got 27 mpg, at 75 it went down to 25.5 and at 80 it was at 24.7... This has been pretty consistent with my car.