I decided to drive to work on my truck all week at 70mph and got 13mpg, kinda sucky, was expecting 17,18mpg (

Would air leaks cause lower mpg?
Tires pumped up
New 6637 filter
New engine oil

Still gotta flush Trans and axles

Maybe brakes dragging or any other things you guys check?

 

With a power stroke, I'd expect more than 13.

 

hand calculated? extended warm up time?

 

Clean your EBP tube and check for boost leaks. Do you have a boost gauge?

 

First off, lets not get stuck on 18mpg. 13mpg is very realistically your truck's average mileage. But that doesnt mean you cant take some steps to try to increase mileage.

And let's also quickly address another issue; the "You drive a truck, get used to it." I hate that response because it is not helpful nor constructive. Yes, our trucks wont get 30mpg no matter what we do, but if there is a problem and we are losing even 1mpg, that is a significant drain and a good indicator to general motor health. Decreasing MPG can be used to indicate to arising problems and shouldnt be ignored or chalked up to "Its just a truck."

Now, to your question...

How many miles to work? How much freeway/city? I get about 14mpg combined city/highway, and can get 17-19mpg highway if I am careful. Some configurations will get higher. Manual and 2wd trucks can get 20+ freeway all day.

There are MANY things that can decrease fuel economy, and the biggest one is the simplest and most obvious. Maintenance; and it sounds like you are aware and on top of it. We have heard it all before, tires, air in and out, and filters. Those are the keys to MPG.

I am going to go over all of the things you should be aware of, some of which will have much more effect than others. None of these will boost your MPG a huge amount, but also are part of routine maintenance anyway. As I mentioned, a lower MPG could indicate to a maintenance problem. But it could also just be an aging motor, which is why I dont recommend anything for MPG resuscitation that cant also be considered good maintenance.

Tires: You said they are aired up. Good, that is the easiest and most effective step. Now look at the wear. Is it even? If not you may need an alignment or have other front end problems. On these heavy 4x4 trucks alignment can go out, and it is important to have it rechecked about once per year. An excessive toe in or out will cause increased rolling resistance, and, you guessed it lower MPG.

Also, the obvious, larger, wider, heavier tires create more drag.

Technically not apart of the tires, but wheels are just important, and what is connected to wheels on a 4x4 truck? Hubs. Ford ESOF hubs like to stick, and not unlock after 4x4 is disengaged. This harms nothing because the transfer case is disconnected the transmission, and the transfer case and differential both have their own lubrication independent of everything else, however it does create drag and a locked hub can contribute a solid MPG point to the board.

Air in: How is that air filter? Its more important than you might think, and an aftermarket is not necessary for trucks at or near stock power levels. For increased filtration and extended filter life you can get an aftermarket filter such as a 6637, but there are some people who believe this filter can reduce 6637, while others say there is no evidence to support these claims. I run a 6637 but also believe the stock filter is acceptable for most users.

Inspect your intercooler boots. Over time they seep oil residue from the CCV return hose and this will permeate the boots and can create boost leaks. Boost leaks translate to lower MPG. If they are oil laden take them off and clean or replace them; aftermarkets are available.

Air out: Exhaust doesnt start after the turbo, in fact most of the problems are between the engine and the turbo. Inspect the manifolds and the up pipes for black soot streaks. They are very common and indicate to an exhaust leak, which also causes lower MPG.

Backpressure is a very hot water topic. It is hard to create extra back pressure with a turbo between the tail pipe and the engine, but a significant restriction will increase back pressure. The only way this would happen is if a foreign object was introduced into the exhaust pipe, mud perhaps. Other than that I cant imagine a situation where you could increase backpressure enough to effect mileage.

Speaking of occlusions effecting backpressure... What if you didnt completely clog your exhaust, but your engine THOUGHT you did? Enter the Exhaust Back Pressure Sensor. The tube for the sensor is plumbed into the passenger side manifold, and often clogs with soot and can cause the PCM to collect false back pressure readings.

Filters: This is HUGE. Air filter, oil filter and fuel filter. Change them, change them regularly and change them often! Air filter every 5,000 miles (unless an aftermarket is in place), fuel filter every 15,000 miles, and oil filter every 5,000 miles (unless UOA indicates extended OCI is feasible). Motorcraft has set a great standard for all three and OEM filters have proven to be top notch for those three applications. In fact OEM (or OEM supplier) is the ONLY filter I recommend for Fuel and Oil.

There are also many other things that can do lower MPG. Most of which fall under the <1% category, things like differential fluid, transmission fluid, etc.

In summary, I probably missed a lot, or over-stated, under-stated, mis-stated or otherwise made an error or omission. It's late, and I just got off a long shift, but I hope I contributed something useful. I rewrote this probably 3 times so it may be a garble when I wake up in the morning.

 

Fantastic post, Trey!

I'll take the lazy way out... click the last link in my signature.

We are currently getting a lesson on cold auto transmissions dropping MPGs a little.

 

could you explain?

 

Here's the [LINK]

Mark is an automatic transmission engineer... so his word has gravity here.

 

I concur from experience...having tranny temp around 170 definitely increases fuel economy when it gets cold. I use a Derale Thermostat on my truck.

 

Clean that ebps tube like mentioned. Boost leaks like mentioned can cause low MPG.

What RPM are you seeing at 70mph? For the best mileage you should try to run just under 2000rpm.

Do you have a catalytic converter on your truck?

 

What should the EBP reading be?

 

Anytime u cross the 2k mark on rpm, the fuel mileage dips quite a bit as well.

 

That is what I was thinking at 70 he is probably above 2000

 

my work is about 95% free way, about 25-30miles each way.

im sorry what is the EBPS tube? i do have some oil build up on intercooler pipes here and there, would that be part of the issue?

there is no cat and im at exactly 2,000 at 70mph

i have a boost gauge yes, im at about 1-2 psi on freeway going 70mph, seems about normal

i do warm up for a few minutes before i go yes, and i have a MPG app and also did it by hand, both are same.

got 340miles on a tank and filled up at 25.6 gallons

 

great write up, i appreciate it, and ill be working same job for the next month or so and ill try to do things and try again, do things and try again, and we will see how things improve if any.

the previous tank i was driving as easy as i could, this time im just driving normal and see how much difference it makes and if even worth the trouble of trying so hard for 1mpg extra