Fuel Economy Seems Really Bad?

I felt like my fuel economy was pretty bad, so I have checked it over the past two tanks and I'm averaging 13.9 MPG on the interstate.

I travel half way across the state and back once a week for work, so both tanks were on the same stretch of road. I filled the tank (with premium fuel, like aways) until the first click, which was 19 gallons. I drove it until the light came on - both times, I got 246 to 248 miles.

I have 285/75's, so my speedometer is 7.2% off at 65mph, according to my GPS. I drove with the cruise set at 65, which is actually 70mph.

Accounting for the odometer being off, I actually got 265 miles on 19 gallons, which is 13.9 MPG.

Now, I have modifications to my truck - and I know they are hurting me. I have a 3" lift, 285/75 BFG MT KO's, an ARB front bumper (no winch), stock wheels, Yakima cross bars with farring. 131K on the odometer. I have replaced the spark plugs (with OEM units), cleaned the throttle body and the MAF sensor (within the past 10K miles). I have changed all the fluids (both diffs, transmission, t-case) and I've always used synthetic engine oil, changed every 5K miles with an OEM filter. I have a K&N air filter in the stock box. Stock exhaust. It's a 2006 DC TRD OR, 6 spd.

Does this mileage sound normal to you guys? Or should I consider checking for other problems or inefficent sensors? I know I won't get 20mpg with the way the truck is set up, but I'm concerned that there might be something that I'm overlooking...

Thanks!

 

Yea, those mods will hurt MPG.

What PSI are you running in the tires? That could really affect MPG.

Are there hills/mountains in your commute? Cruise may also be hurting your MPG if it tries to gear hunt too much.

 

I'm not sure what you mean by premium gas, but I think your truck probably only requires the low grade. Not sure if that could hurt gas mileage however.

 

Won't hurt.
Might help a very small amount on the V6 as the ECU will run slightly more spark advance to take advantage of the higher octane.

Won't help at all on the 2.7.

 

Welcome to the club. I go through gas like underwear, the roof rack and tires/lift doesn't help one bit.

Are you 4x4 or Prerunner?

 

On the tire pressure - I run 29 in the front, 32 in the rear. Any suggestions there?

I am, indeed, due for a cleaning on the K&N. I do that.

Wheel bearings - I haven't had any other issues, so I doubt that would cause it.

This stretch if road has rolling hills. Since I have the 6spd, the trans doesn't hunt for gears.

And it's a 4WD.

It sounds like I am just reaping the harvest if my modifications... Yuck.

 

The ARB can weigh down the front A LOT. I'd run at least 35-40psi with that much weight on the front.

And yes, the added weight of the 4WD components doesn't help. I'd say with your specifications, you're just about normal for those mods.

 

I run 40psi

 

I am basically all stock (no lift, no engine upgrades), and I get between 18-23 mpg depending on how much city driving I do.

I would think, with the OP's mods, and if he raises his PSI, he will at best see between 14-17 mpg.

 

You're also a Prerunner.

 

Hell, air is free. This is the best news I've heard all day!!!

40 psi it is!

 

Yea make sure your not going over your tires rating. I have a E load and they can handle like 80-90psi(id never go that high)

 

Thread jack: My mechanic said to do 40 and put in 40psi. Truck recommends lower.
I have stock 2013 take offs from a TRD sport. I was going to drop it down for fear of premature tire wear in the center of the tire...haven't done it yet cause I am that lazy.
Bad idea? 40 is good on stock wheels/tires/suspension too?

 

On stock tires I would probably go with the factory recommendations since I'm sure Toyota done there testing. You could play with the pressure a little tho and see if you get a difference.

 

Truck recommends lower because:

1 - Truck recommends a balance between comfort, tire wear, and fuel economy
2 - Truck recommends for factory tires.

The moment you take the factory tires off and go with a different type/rating, the door inflation levels go out the window.

But even with standard Firestones on my 5-lug, I'm running 45psi and getting 24-26mpg.

The max sidewall pressure is NOT the pressure limit of the tire.
That is part of the load ratng. Read the WHOLE THING... it will say
"MAX #### POUNDS @ ##PSI COLD"
It doesn't say "MAX ##PSI COLD"... it says "MAX #### POUNDS" and gives a pressure for that max load.

At lower pressures, the load capacity is derated. At higher pressures, the load capacity remains at that sidewall level.
Also, higher inflation = higher speed at which the tire will hydroplane... wet traction is better.
Cornering and dry traction is better due to reduced tread squirm.
Tire life is increased due to heat reduction from reduced sidewall flex.

The only downside to running REASONABLY high inflation levels is the ride quality.
And just a note, I've been "overinflating" for 30 years and have never once had a tire wear out the center before the edge.

 

These are load range E tires.

I learned something today - thanks a lot guys. I've been using the 29 and 32 bc the door said so.

I'm going to finish out this tank with the lower pressure, as another control test. I'll go up to 40 for next week's trip and report back.

Thanks again!

 

Ditto on my Silverado.
80 if I was towing.

 

Update: I went up to 40psi in the tires and my fuel economy went up to 14.4mpg. That's a gain of 0.5mpg just by changing tire pressure. Pretty good, in my book.

Follow up questions - what is the capacity of the fuel tank for a 2006 DC SB 4WD? It seems like I read that it's 22 gal, but I'm not sure.

Also, any idea as to how much fuel is left in the tank when the light comes on?

 

All 2nd Gen are 21.1 gallons
Low fuel light varies, but typically you'll have between 3.5 and 4.5 gallons left.

If you're getting 14mpg, I'd plan refueling stops at around 220 miles... no reason to push it because strong wind will hurt.

 

That tire size for sure is hurting you. I went from 265/70-16 to 265-75-16 tire size. MPG I was getting was about 18 mpg, now I'm getting 16 mpg.