When I'm really good and stay at 70mph, I can get nearly 19. Below is how I keep my records in order.

 

Your long term average is 16.17, My 01 is 13.8 it's a 4X4 CC LB with 305s on 10" wheels. Before all my Mods I averaged 17.1 But my mods has cut that!! Programmers/Chips DON'T increase Fuel mileage!! I've tried 3 brands and none of them increased my Fuel mileage!!

 

Holly crap! That is the most detail log that I have ever seen! That is incredible!

 

It takes about 2 minutes at each fillup to record the details in my notebook in the side pocket next to where I sit. In fact, it really takes less than that because I document most of the details while filling up. Aside from that it takes another 5 minutes once per month to update my spreadsheet where the MPG calcs are done.

I don't worry about calculating MPG on each fillup just to avoid being too miniscule in my attention... I just capture the basics (miles driven, total vehicle miles, gallons used, date, fuel additive type/quant, hwy-city-mix, and maybe a note about how I drove or anything else that could significantly affect mileage).

The main reason I'm doing this is to track how my mods affect mileage, if at all, which is why I have the entries about maintenance and modification tasks. You see, this is my first diesel truck ever, and I am learning a lot in the process. So far, I honestly can't see a significant relationship between my mods and mileage. There are too many variables involved to separate the issues accurately (time of year, winter/summer blend on fuel, type of driving, mph during drives, mods installed, etc).

Here's what I have learned, though, which is probably the most valuable lesson for me... the mods I've been performing have been primarily targeted at increasing cleanliness and expected life for my engine and its components. Some of the mods may slightly affect mileage, but I will probably consume those small increases in slightly more aggressive (fun) driving due to the slight power increases associated with them. Even if I never see an increase in MPG, I can be content knowing that I've probably improved the expected life of my engine.

 

Spreadhseet? Oh man, are you this thorough with everything? I have a project planner with receipts and records on my truck and old emissions tests and a notebook where I record things done, oil changes and mileage..and I thought I was doing good..
<O

Next time I take a vacation from work you want to sub for me? I'd come back and my desk would be spotless and organized, alphabetized, and all my work chronicled. <O</O

 

Do you not tow anything? or do you have another log for that. In either case, I think I am going to have to start a little log book myself.

 

LOL. I might be willing to consider it for a phenomenal fee, Lisa, but the distance between where we live would make it pretty difficult. Actually, my desk always looks like crap. I keep my electronic records in perfect order, but my paperwork is managed by what I refer to as "organized piles". You see, "work" is work, and my truck is, well, my "haven".

 

They say that the most organized people put things in piles like that.

Now so I don't divert from the subject of the thread too much...I'll say that I seem to get a little better mileage than the norm with my '99. On ALL highway trips, not towing anything, and keeping my foot out of it, I can see 20-21 MPG. City-Highway mix driving I have seen as high as 18. Of course I had calc'd these numbers from fillup to fillup...based on the miles traveled and the gallons added. There is some room for error because my speedo is off due to the big tires, but I believe it would work to my favor. Worst mileage I have seen was 14, in the winter and running Power Services anti-gel. My truck seems to see about 2MPG jump when I run DK in the grey bottle.

Edit - does anyone know if maybe the high altitude here can account for my good mileage? I wasn't sure if that was a myth or not.

 

As an engineer, I can say that it is a Myth. At higher altitudes, the air is "thinner" because it is at a lower atmospheric pressure, which means that it has a lower density (lbs per cubic foot). This also means that the oxygen content is lower in any given volume of air at a higher altitude.

In a conventional gasser, the air intake system is limited to how much air it can trasnfer into the engine's combustion compartment. Since that is true, if you feed it lower density air (from a higher altitude), your engine will be seeing an air/fuel mix that is richer in fuel. However, it needs the oxygen to burn properly, so there would be a slight reduction in combustion efficiency. Obviously, tuning can compensate for this reality and in the end you wouldn't see a lot of difference in mileage overall.

In our PSD's, since we are running with a turbo that compresses the air to such a high degree in the cobustion chamber, the small difference in air density will hardly make a difference. Even if it could make much difference, the MAP sensor will compensate for the air density issues so that again, you will see virtually no difference.

 

Cool. Good explaination. An engineer...the spreadsheet is making more sense now! My BF is a mechanical engineer. He'll talk and try and explain things to me in technical terms and this is what I hear. BLAH BLAH BLAH Truck BLAH BLAH BLAH MOTOR BLAH BLAH BLAH TURBO BLAH BLAH BLAH Want to go have a beer?

Ok so since I really should be getting worse milage, if any noticable change at all, due to the atitude, i'll feel very lucky I get the MPG I do these days.

 

These types of MPG discussions are why I bothered to post the download of a HOT supermodel with BIG BOO... , so users can plug their truck diff and tranny ratios, tire size, etc... and other relevant mods into the model and see their MPG. I'm quoting my result from the model below, and it predicted my actual MPG very closely.

"An AFR=35 matches my empty cruise exactly, at 65 MPH (2000 RPM) it takes BP=4 psi to get the required 69 RWHP, and for that combination of RPM & BP with AFR set to 35, the other tabs show GPH=4.3, and MPG=15.1. I included a pic of the AFR=35 example below. At 58 MPH, you get 17.9 MPG, and this drops to 15.1 MPG at 65 MPH. I've posted my drag model before explaining how the required RWHP increases as the (MPH)^3!"

You can see my wing in my avatar, and even though it folds flat for running empty, it still causes some extra drag which is included in my model, so my model will somewhat under estimate the MPG for a more streamlined stock truck. However, as shown above, your exact MPH makes all the difference in determining your MPG. The net drag and therefore the required RWHP to propel any truck at a given MPH increases as (MPH)^3! This means your engine has to generate twice as much RWHP to go 70 MPH as it does to go 55 MPH. Discussions comparing MPG are pretty much meaningless with out including the exact MPH.

When I start seeing claims for high MPG with no discussion of drag, MPH, and just how the fixed BTU/gal gets more efficiently converted to RWHP, I'm wondering just what such claims are based on!

 

I understand what you are saying and I think that I can shed some light on something for you.
I think what they are based on are peoples actual overall fuel mileage tank to tank or over a given length of time. All the figuring in the world with co-efficients of drag etc., won't change what it actually works out to be when you fill up.

 

I think I understand what you're getting at, Ernest, but you didn't quite get it out in clear terms.

Claims for high MPG can be based on simple math alone and be both meaningful and true (you know, miles travelled divided by gallons used... pretty simple math). No discussion about drag, mph, or anything else has to be had for the numbers to be correct or valid to the discussion.

On the other hand, for the discussion to be MOST meaningful, some context is needed, and this is where mph, tail wind or head wind, load being pulled, elevation changes over the trip, etc. can help create improved understanding as to whether or not one eprson's claims about mileage are meaningful to me.

Drag, though, as real as its impact is, is not an easily measured variable, which means it can only be discussed in very loose terms.

 

Well, the laws of physics say what's possible and what's not, that's one of the reasons I did my model. I'm not disputing any particular MPG claim on this thread, but I've seen several claims in the past that simply aren't possible! When you take 130,000 BTU/gal, and convert it to HP, and compare to some MPG claims I've seen, they seem to defy the second law of thermodynamics.

In any case, I thought the theme of this thread was what mods to make to improve your MPG, and how much improvement might certain changes make. All of these issues are contained in my model, that's why I was suggesting that it be looked at.

 

According to my model, changing nothing else except the atmospheric pressure gives the following... 1) an atmospheric pressure of 14.7 psi at sea level gives 260 RWHP at 2800 RPM & 20 psi BP, and 2) an atmospheric pressure of 10.2 psi at 10K ft altitude gives only 218 RWHP at the same RPM and boost!!! My model says that the lower ambient atmospheric pressure at altitude makes a big difference in the HP a diesel can produce.I'll agree that it's difficult to just take some measurements of the size and shape of an object and calculate in advance the drag force on it at a given speed, that's why wind tunnels are used to measure it on scale models, etc..., but it's pretty easy to measure the drag force on your truck fairly accurately.

I've used various techniques for calibrating my drag equations (both truck & truck+trailer) for my particular set up, including timing how long it takes to coast in neutral from a high speed to a lower one on the flat (kind of the reverse of a drag strip calculator), coasting down known % grades and timing my rate of speed increase, and seeing how well I can tow marked % grades and relating that to my measured RWHP from two dyno runs. The one calibration that I haven't tried (wife won't let me, and I've never had a place to try on short trips when I'm alone) is a speed run to measure my RWHP limited maximum MPH, which my current model estimates at about 105 MPH.

For a stock truck I suggest this equation instead of the one in my model which includes the effects of my wing in it's stowed position.

Truck only, RWHPR=Rear Wheel Horse Power Required...

RWHPR = (0.35)*(MPH)^0.8 + [(MPH)^3]/(5000) + [(GCW)*(%Grade)*(MPH)]/(375)

The first term accounts for rolling friction (tires, bearings, etc..), the second term is for aerodynamic drag, and the third term is for % grade and should be entered as a decimal, i.e., 0.05 for a 5% grade.