Decrease in Fuel Economy - Trouble Shooting

[true_north]

First off, a little background info. I'm driving a 2008 4.0L 4x4 supercab, standard trans. It has 80,000 km (49,700 miles) on it, and stock (not even a camper shell, back rack, bull bar, or otherwise dead weight).

All last summer, my mileage was all within the stated 15 to 19 mpg range, and that's with my 265/85 R16 All-Terrain summer tires. Come November, and cooler temps, I put my winter tires on (stock 255's) and coincidentally, noticed a significant decrease in MPG. Now I highly doubt it's due to the tire swap; if anything, the swap should have brought my MPG's up slightly.

In December, I decided I had to do something; on some tanks, I would get down to 10 MPG, even while driving like an old lady.

Based on research on the forums I did the following:

-cleaned MAF
-cleaned throttle body
-new spark plugs & wires
-fuel filter change
-synthetic oil
-new air filter

Basically, a standard tune-up. After the tune up, I noticed a slight increase. Up to 12-13 MPG (city). I figure it's pretty close to the posted 15 MPG (city), but seeing my truck get that whole 15 MPG would be nice. I mean, last summer I spent a day towing a 12x6 box trailer, and was getting 14 MPG! I should be able to do better than this!

Is there anything else I should be looking at?

I should point out that in winter temps (14 F and below), my parking brake locks up like crazy overnight, even more when the day before was warm. Some morning the truck won't even budge. I need to gun it in 1st and pop the clutch to free it. Very unpleasant to say the least!

Could it be possible that my parking brake is partially engaged, and dragging on my wheels? Or is that crazy?

Any thoughts? I'm all ears...

 

[adsm08]

It is possible that the brake is sticking and causing extra drag.

Cold weather will kill MPG as well as the engine uses more fuel trying to get up to temp. If you are letting it sit and warm up like you should there is even more that you are losing to time spent idling.

 

[true_north]

Completely agree with the cold weather aspect. In past years, I've definitely seen somewhat of a drop in MPGs over the course of the winter, but most recently it's been worse.

Would it be worthwhile changing the diff. oil? I suppose it wouldn't hurt eh?

 

[1996DANGERRANGER]

winter fuel will cause it. i see a drop in my mpgs every winter because of the fuel.

 

[AlaskanRider]

My subie drops from 27-29 to 18-20 mpg when it gets cold out. Even when I dont change tires.

And the above post mentions different fuel, which I googled, and apparently they do change the fuel seasonally.

Worth checking stuff out, but good chance is theres nothing wrong with your truck. And I would figure out a way to not need to park with your E brake. In fairbanks AK its standard practice for everyone not to.

 

[Sasquatch_Ryda]

Are you accounting for the difference in tire diameter when you are you mpg calculations? Larger tires throw off the speedo and odometer.

Sent from my SGH-I747M using Tapatalk 2

 

[adsm08]

And the above post mentions different fuel, which I googled, and apparently they do change the fuel seasonally.

They have to. Summer mix fuel has more stuff to make it resistant to ignition. If you run winter mix in the summer it will ping like crazy and if you run summer fuel in the winter it will miss.

 

[bodkin1]

You probably could install a block heater:
http://www.amazon.com/Kats-11416-Watt-Frost-Heater/dp/B000I8YOUQ/?tag=959media-20

 

[true_north]

So I've got a quick update on this whole situation.

Last week I was on the road for work, and did about 650 highway miles. I consistently got 21 mpg on my tanks (11L/100 km). I was quite pleased.

I'm curious to see if my city mileage improves slightly now. I hadn't done any long highway miles in a long time. I know with my last car, a '97 Volvo 850, lots of city driving in colder temps bogged down the engine quite a bit, and a good highway drive made things better. Mind you, that was a 15yo car.

We'll see...

 

[BRUTUS_T_HOG]

First off, a little background info. I'm driving a 2008 4.0L 4x4 supercab, standard trans. It has 80,000 km (49,700 miles) on it, and stock (not even a camper shell, back rack, bull bar, or otherwise dead weight).

All last summer, my mileage was all within the stated 15 to 19 mpg range, and that's with my 265/85 R16 All-Terrain summer tires. Come November, and cooler temps, I put my winter tires on (stock 255's) and coincidentally, noticed a significant decrease in MPG. Now I highly doubt it's due to the tire swap; if anything, the swap should have brought my MPG's up slightly.

In December, I decided I had to do something; on some tanks, I would get down to 10 MPG, even while driving like an old lady.

Based on research on the forums I did the following:

-cleaned MAF
-cleaned throttle body
-new spark plugs & wires
-fuel filter change
-synthetic oil
-new air filter

Basically, a standard tune-up. After the tune up, I noticed a slight increase. Up to 12-13 MPG (city). I figure it's pretty close to the posted 15 MPG (city), but seeing my truck get that whole 15 MPG would be nice. I mean, last summer I spent a day towing a 12x6 box trailer, and was getting 14 MPG! I should be able to do better than this!

Is there anything else I should be looking at?

I should point out that in winter temps (14 F and below), my parking brake locks up like crazy overnight, even more when the day before was warm. Some morning the truck won't even budge. I need to gun it in 1st and pop the clutch to free it. Very unpleasant to say the least!

Could it be possible that my parking brake is partially engaged, and dragging on my wheels? Or is that crazy?

Any thoughts? I'm all ears...

Low temps and winter blend fuel= low fuel economy. Solved.

That cloud of white steam coming from the tail pipe in the morning is mostly condensed fuel droplets because the engine has to run very rich to get enough fuel vaporized to run.

 

[true_north]

Agree with you Brutus, I was just surprised that it was such a drop, but also relieved slightly when I found that highway mpg's are where they should be.