Yep, that's the only way to figure MPG.
Miles/Gallons=MPG

If you drive like there's an egg under your foot (brake and gas) the MPG will get better IMO. That's just no fun though

 

Re-read my posts, I've always said on here I'm totally new to diesels and learning daily. I've never claimed to know very much if anything for sure other than what y'all have taught me and I've accomplished. I know mpg is for all cars not just diesels. I'll do another mpg test on my next tank and see what I get. The most confusing thing for me has been that know seems to know FOR SURE exactly what size the tanks are. I mean when my gas gauge is deep in the red and I've run it for another 40 miles but according to some on here I still have 5 gallons left. This is confusing, or my gas gauge isn't very accurate.

 

I guess I was taking your comments as a little contemptous...sorry. I new you were new to diesels but MPG is MPG. Math, pure and simple. The bottom of the tank is the same, Even gassers have quite a bit of fuel left in the tank when empty. I usually go 200 miles on each tank before switching or re-fueling. I've never run the tanks even close to empty anymore. I did it with my old IDI (1987 6.9 diesel) and had to buy an injector pump right after that. Big $$. All gas gages are inaccurate, it's just an estimate IMO. I don't even need a gas gage anymore, the odometer tells me when it's time to fill up. All this talk about fuel tanks remind me, I need to go out and replace my rear tank, it sprung a leak. Damn Michigan winters. I'm going to run it dry, I bought 2 fuel filters just in case. We'll see how much is left in the tank when the engine sputters.

 

Even though I'm a teacher if you start using big words like "contemptous" you might lose me-LOL. I'll admit I drive it easy arouind town. My thought process is: I have to pay and fix everything I break on this truck so I really probably baby it a lot more than most people. I have checked it's power from time to time and it has good power! Thanks again for all y'all's help!

 

tn, I am still intrigued as to the performance of the marvel mystery oil, I have been putting 2 stroke oil in my fuel and saw a .5 mpg increase in my average, (and I watch religiously) I have often considered dropping the MMO in to see how it did. When you started running it could you tell a difference?

 

I guess at the end of the day, it relly doesnt matter to me what my mileage is. I am going to keep driving my truck regardless of how much fuel it is burning!!

 

Hey Fellas, this is my first post, but I've been reading with interest since I bought my '96 PSD XLT X-cab 5 speed. Still mystified by chips and 10k mods, but mileage I can understand. My truck has a replacement clutch that apparently has moved the springs from the fly wheel to the clutch plate (hope I got that right). No idea if the gears are 4:10 or 3:55, but when I drive the back roads (at slower speeds and lower RPMs) I calculated almost 23 mpg (odo miles/gallons in at fill up). On the highway (70 mph at 2500 RPMs) it went down to about 16. Does this seem right? Is that kind of high RPM's for that speed? My odo is probalby off some, but the tires are stock (so is everything else, I think).

Anyway, just wanted to get into the conversation, and hear your thougths. I'd sure like to get 20 mpg if there is something I should be doing differently.

And feel free to discuss the top ten modifications I should consider. Although I'm pretty inept when it comes to DIY, I like the idea of learning and know a few guys who could help show me the way.

 

Hi Pete and welcome to FTE!

Check your door sticker. Your axle code should be listed. I think I have this right:
3:55 Open is code 39
3:55 Limited Slip is code C9
4:10 Open is 35
4:10 Ltd is C5

Best way to max your mpg is to make sure you have clean fuel filter, clean oil, and go easy on the accelerator. Most of us find the best MPG if we keep the rpm's below 2000.

As far as you mods go, why don't you start another thread. You will likely get more responses that way.

 

Just spoted the Mods thread. When my muffler goes, I think I'll go for the exhaust mod. Have you heard about the clutch upgrade I have? Any thoughts on the rpms I'm running at highway speed?

 

Jim sounds like a good time for a bronco tank upgrade! can you say 52 gallon capacity!!

To Pete in Maine from the sounds of your RPM's at 70 mph you have 4.10 gears. The 2500 rpm is the reason for your drop in mileage at highway speeds. Your right on wiht your clutch being different. stock they had the springs in the flywheel. aftermarkets have the springs in the clutch plate like the rest of the world.

As for mods to do see the "official Mod thread" that is somewhere here on the first page of threads.

 

Pete, welcome. I would get a pencil and paper and comb the threads here making a list of the potential things that you can easily do, while making a list of the not so easy to do. Then you can prioritize the list in order of ease and cost as well as time in man hours. There are MANY simple things you can do to your truck to get it performing better for very little money and little time. There are mods that are costly but easy on time. Hope this all helps. There is a wealth of info in here from guys that have done the work before and can make your job much easier!

 

Pete, I am guessing you to have a 410 ring gear. With my truck I am at 2300 RPM doing 70. 16 mpg at 2500 RPM is average for these trucks running empty.

 

Is it cost effective to switch to 3:55? What does that mean for my low end? Empty, I typically start out in 2nd gear because first is so low. If it isn't obvious, my knowledge of things automotive is pretty limited.

Suber, I have been doing just that. Baught the truck to pull my boat, but suspect I'll end up under the truck more than on the water thanks to all the FTE info I'm gathering.

 

It can become a neurosis for sure. There is a fine line between being obsessive-compulsive, and simply enjoying your truck.

 

Basically your tanks are 18 & 19 gals. AFTER I modified the filler necks, I could fill the tanks up to the lip everytime and I beleve it made my milage calculations more accurate. 375,000+ miles without any additives & engine has never been opened up. Origanal injectors, fuel pump, oil pump. 10,000 miles between oil changes with Rotella 15w40 dino oil. You don't need to do anything to these trucks to get long life & great service out of them.
I have also run my tanks out just to see how low the gage will go. It goes well over a full needle width below the red mark. From EMPTY (when engine quit running) to FULL ( fuel sitting at the top of the filler neck) I have put over 20 gals in each tank.
Looking back over the last 200,000 miles the furthest I see between fill ups was 738.9 miles (if you don't count the 782 where I cheated & added 6 gals to get to a cheaper station, 42 gals total added then) Lots of 600+ fill ups.
Come winter time & winter blended fuel, your mileage will go down.
Best mileage I noticed was 23+ MPG and worst was 9+ MPG. Summer I average around 18 & winter around 16. (unless I let it idle for 15 or 20 hrs.)

BTW Cuda_jim... Remember the fuel pick up is on the BOTTOM of the tank so you already have "sucked up" all the gunk & crud (& water) in the bottom. Running the tank dry shouldn't get you more stuff that needs to be filtered out.