In the quest for MPG I have made some miraculous gains. When I got the truck I was getting 6mpg on the highway. Its up to 16 now.

Anyways. The evil thing about it all is the best gas mileage I have gotten and the conditions I received this in.

20mpg. Barreling down the 10S to Tucson. Was doing 80 the entire way there.

22mpg. Crawling up the 260 to Show Low. 6-8% upward incline from Payson to about the Heber Overgarrd area. Doing about 70ish in fourth with the pedal mashed completely to the floor.

13mpg. Doing 65 on daily commutes to work on a fairly flat freeway.


What the heck? I push the thing a little and I get better gas mileage? Don't make sense.

I babied the thing in and around town. Got 16.8mpg doing that. Drove it normal and got 16.3. Started hammering it and mileage went to 16.4. Am I to assume demonic possession or is there a rational explanation for this?

 

Well just a hunch but maybe your truck does not like to go to work any more than the rest of us?

Seriously though your mileage is always going to be much better in any situation where your throttle stays put. My Dakota 316 V8 gets 13.6 to and from work and about 22 on cruse control heading to a friend of mine 75 miles away.
Since you get so much better in those situations you may want to look at gearing and your engines "sweet spot" maybe it runs more efficient at those speeds and RPM's? My brothers Dodge diesel gets better mileage with a loaded car trailer than it does running empty. We got almost 6mpg better mileage coming back loaded than we did going down empty to get my parts truck from Oregon. The parts truck was a complete 1959 F100 4X4 and even with that big block behind us he got better mileage.

_____________________
My Grandpa told me once that you have to learn by the mistakes of others because you will NOT live long enough to make them all yourself.

 

Goodness grief, 6 mpg on a straight six. Glad to hear you've got it running better now. To answer your question, it's hard to draw conclusions based on fluctuations in the 0.1-0.5 MPG range. With changes that small, your odometer or the shut-off valve in the gas pump nozzle could contribute to the variability just as much as anything on your engine. I've also heard stories of poorly maintained gas pumps that start counting, a split second before the gas actually starts flowing. Random things such as that make it hard to pull apart where something as small as a 0.1 MPG increase is coming from.

 

Yes I agree. Two tankfuls ago I got 25, this last time 17. Alot depends on the shutoff valve. The only good way is to test over multiple tankfuls and calculate it on the whole bunch. So what did you do to make such an improvement?

 

Drastic improvements to gas mileage were cause by these factors.
1. Jackass I bought the truck from did 0 (ZERO) maintenance to the truck for 6 years. Damned lucky the truck was still running when I got it or the truck is that damned good.
2. Drained the 80w-140 gear oil out of the diff and tranny. Flushed three times with 75w-90. Put 75w-90 synthetic in the diff and synthetic ATF in the tranny (basically what was supposed to be there) with a quart of synthetic lucas in each.
3. Replaced the spark plugs seeing that they were OE from 1990. Might be a slight exaggeration on my part but not much of one. Made a call to the original owner and got this for a response. "Spark Plugs?"
4. Replaced cap, rotor, and plug wires with that. Installed brand spankin new MSD coil.
5. Replaced every frickin part of the emissions equipment on that truck. From thermactor to vacuume solenoids. Actually reduced gas mileage but the truck runs much better afterwards.
6. Drained the three year old 15w-40 out of the crankcase. All two and a half gallons of it. Put Mobil 1 synthetic in its place.
7. Ripped off the old rotted out OE exhaust and put a 2.5in cat back with magnaflo muffler to make it sound a little more manly under a load.
8. Re-routed dual 2in intake to single 3in insulated tube to increase air velocity and improve flow through that assbackward mainfold setup they have designed for the darn thing. Basically installed a short ram. Why they didn't go with a 24v crossflow head later on I will never know. Might have actually bought the motor some time.

16mpg is a three year average. The truck seems to hit that on a regular basis. Downside is that I have to maintain 75mph to do so. Saving gas is a hard sell to the cop that pulled you over for speeding.

 

Ok. Minor update. MPG held steady using 2500 on the city and 3500 highway as shift points. Bumped my shift points up a hair. 3000 city and 4000 highway. Been getting a consistent .2 mpg increase.

I know I know. Can't base anything off of something that small. But 4 grand on the tach? Come on. I'm running this thing wide open all the time. It should be going down not up.

Anyways. I really shouldn't complain. I enjoy getting places a little quicker. But if there is an issue then it needs to be rectified before something bad happens.

I dunno. Maybe I hit some weird balance with the run lean on cruising mode, my perfomance chip, cat back, intake, ect. ect.

 

10 qts of oil?

 

whats the specs on your tranny and rearend? reason being :
i have a 1990 f150 4.9 fuel injected motor, someone put a piece of junk 3spd in it and it sucks more gas than anything i have driven... BUT last spring i had a 16 foot trailer on it with at least 1000 lbs of lumber in tow, i got 3X more mileage with a load than without . . . but if i drive around with out a load, i can get about 20 miles to every
1/8th of a tank. you must also take in mind where your driving, some engines do better in higher altitudes and some do not. cold weather, warm weather its all where your at and how your driving. thats all. PEACE!

 

Actually use 7 quarts of 10w-30 synthetic

 

Tranny's a five speed manual. Rear end is supposed to be a 3.55.

I also use premium and only premium. Have some weird universal performance module that I picked up for my ricer before I got the perfomance chip and before the car was stolen. Advances timing and adjusts the fuel ratio to a flat 12:1 I think. Reccomends premium if you run the module in its highest setting. I run it at the highest setting. Ran it through emissions and it passed with flying colors so im not complaining. Also lets me push the motor to 4k with the short ram, K&N air filter, and cat back. Think my next fun little trick is to install a MSD ignition module to the thing to compliment the MSD coil I have on it.

The truck runs great at 5000ft +. And as with most vehicles, the colder/denser the air the more umph I have behind the pedal.

And before you ask. Yes, all that stuff makes one hell of a difference. It's no Porsche but compaired to what it was I almost feel like im driving the 5.0. Not that the 5.0 was impressive at 180hp (1990).

 

Do you think that the motor is running to rich in the lower rpm, causing it to use more gas?

 

Thats a possibility I have not considered. Does kinda do the hitch and jerk thing at around 1200 RPM from time to time. Usually goes away when I open it up.