Why is my mpg so bad?? 2006 4.0 6MT

am i an idiot or..? i do drive a little heavy footed but intentionally took it easy on the most recent tank to see if id be better on gas around town. the first two are my drives to and from VT up rt 89 going about 80mph the whole way so i figured the high rpms killed it (but why so bad??)

just did the most recent tank of driving around town and totaled 13.6mpg. that seems absurd.

can i just not do simple math? why is it so terrible? im currently on snow tires and theyre Load E rated 245/75/16 (yes heavy but not 33's)

no lift besides 3rd gen trd sport coilovers up front.

i have a magnaflow muffler but no tune or anything.

any help is great

heres the trucks current setup...

 

Are those tires larger in diameter than stock size?

If so, you’ll need to adjust for the percent they’re bigger.

 

If a tire is 10% bigger in diameter then the stock tire, it's 10% bigger in almost all respects, rolling distance, revolutions per mile etc. Add 10% to the miles traveled, and divide by the gallons consumed.

 

10% added will still suck. Best not to look. I learned that a long time ago. Lol

 

What brand tire? Load E is like 55 lbs. usually. I always get load C or D and save like 10 lbs. a tire. Guaranteed you under estimated tire weight.

How old are your plugs?

 

I get 17 to 18 on my p rated falken wildpeaks.
80 mph kills mpg. I would try driving slower but honestly, that seems about right. I usually drive 5 over the limit on the highway for half the tank and the rest being city.
You could try skinnier tires but it's probably not worth it.
In conclusion, don't look at your mpg to be happier.

 

Tires are stock size guys. The E rating won't effect your fuel mileage as long as you stay with, or close to factory size.

"Around town" for you may not be the same driving conditions for "around town" for someone else. The 16.7 mpg number is pretty close to normal for most people. My daily driving is on mostly 2 lane rural roads with some small town driving. No true stop and go driving and sitting at a bunch of traffic lights. Around 17mpg is typical for my 07 4X4 with auto. It has been that way since new and hasn't changed with the E rated tires now on it. But for some driving conditions 13 mpg is realistic.

On Hwy driving, keeping the speed at or under 70 mph I can easily get 18.5-19mpg. I've averaged 20 mpg on some long road trips where virtually all of the driving was on interstate. I've gotten 22-23 once when on rural 2 lane roads in mountains. About 55 was as fast as practical and the long downhill stretches meant I could coast for miles.

Above 70 mph and the aerodynamics of a truck will kill fuel mileage. At 80 mph I'm not surprised at 13-15 mpg. Slow down and you'll do a lot better.

I can't tell from the pic, but it appears that you have a pretty aggressive off road tread on your tires. That will increase rolling resistance and hurt fuel mileage some. But to be honest, it appears that your fuel mileage is pretty close to normal for that truck, in those driving conditions.

 

my "around town" isnt a city, and its also not rural. seacoast of nh. 13.6 seems way to low for around town driving. not sure how old plugs are either, not sure if previous owner replaced them at all. 106k miles ish

 

The tire size may be the same. But is the weight of the tire and rim heavier? That takes more power to get them moving and to keep them moving.
Plus, winter gas. Longer engine warm up cycles. 80mph driving speed and pushing through slush and snow all takes energy.

It all adds up to cut instances that will hurt mileage.

 

An “E” rated tire is likely quite a bit heavier than its p-rated counterpart. It will absolutely affect your gas-mileage (unsprung mass has a huge effect). AT or MT type tread will also increase rolling resistance.

80MPH will effect mileage. But even so, I can typically get 18-19 at 70-75 (with stock size p-rated Michelin defenders.)

 

It really depends on how you drive. I replaced my plugs at 65k and mpg didnt go up. Doesn't hurt to change the plugs though.
What rpm do you shift at to drive normally? What rpm do you cruise at? Do you coast to a stop or do you slam your brakes the last few seconds?

Besides that, only thing that could be really hindering your mpg is tires and alignment

 

Yes it will. It’s more weight, which means more rolling resistance. It’s unsprung weight as well, which is the worst kind of added weight.

The engine has to work harder to spin more weight from a stop. It’s science.

Heavier tires will lose mpg in the city, but can gain some mpg on the highway.

 

This issue has come up a lot - particularly with people buying their trucks used.

I’m a huge proponent of spending the time to change ALL fluids, plugs, belts, cleaning MAF/TB, Pcv, changing filters, lubing u-joints etc. after the purchase of a used vehicle.

It’s likely that OP is dealing with a combination of heavier than stock tires with agressive tread, winter blend gas, and some combination of needing new plugs, and MAF cleaning, maybe a Pcv valve, try some fresh diff oil, etc...

All of those can add up without anything being “wrong” with the truck.

 

You’re also in winter fuel season right now. Winter blend fuels get worse mileage.

 

With 285’s and a heavy foot, highway and town i can get about 14-16 mpg even in the winter with armor and a bumper. Plugs are brand new and i will accept that with added winter air resistance+heavy wind and fuel blend

 

Mines a v6 6 speed lifted on 285 E’s. I get 16ish around town.

Give the truck a tune up, something’s wrong.

 

Seems normal to me.
I was getting 15-16 depending on shift points.
6 speed,V6,2wd,265/75/16,new plugs,pcv,air filter,diff fluid,blah blah blah.

editn second thought I wasn't factoring in the error of larger tire size from stock so I don't know what I was truly getting

 

My 2014 TRD OR, Access cab, 4.0L V-6, six speed manual, has the exact same sized tires in a Michelin Defender, P-metric. In mixed driving, I get about 18. If I'm rolling down the interstate doing 80, it drops a little but I almost always get over 17.
A lighter tire should help. I also run about 35 psi on all four corners.

 

2006 with how many miles?

Most already discussed the potential tire size discrepancy.

Add a few extra psi to each tire. Try 5, and see how she goes.

Being a 2006, your fuel pump and filter, unless you have driven very few miles, need a refreshing. That filter is definitely being a drag on your system.

The Aussie boys have come across that the injectors post 100k has started to not perform as original, and fuel mileage from them alone is directly affected. ~3+ mpg losses. Calculated.

Age and potentially miles are the main factors here.

 

I heard a guy last Friday who got a bigger tank and it really made a difference. I am thinking of putting in the same.