Yet another can of worms...MPG question

You didn't! Did you?

 

What the OP has to ask himself is if the motor has a major event would he fix it? Replace it? Replace truck? I know on paper .2 mile per gallon looks huge after its put to a yearly figure. After dropping several thousand to gain .2 or .5 how much fatter are your pockets really? Just a little food for thought is all. Be sad to drop a wad on the truck and 6 months later its useless and replaced with something totally unlike it.

 

No I didn't trade going to run her and chalk it as education.

 

Just got meaning 30,000 ago lol. i dont know what you heard, but mine started preforming after 15,000

 

Lol, the oily black hose is just as it always was.

The singles alone may not have given .75, but the singles and low rr steers together got .75. The steers were some junk from firestone. I bought the truck cheep planning on replacing the rubber.

 

Have you had your charge air cooler pressure tested to make sure it's not leaking? Otherwise, use your cruise control on flatland, and watch that boost gauge. Anything over 20 and you're burning a good amount of fuel. The biggest thing you can due to increase your MPG is become a better driver. Keep the engine rpms where the manufacturer recommends for best economy, and if that limits your speed, regear it or deal with it. You can put all the doo dads and latest and greatest snake oil "fixes" on, and maybe you'll gain a little bit, but the guys that get the best fuel mileage can increase it in any truck because of their driving skills.

A majority of trucks on the road were purchased by fleets and spec'ed for the best fuel mileage at the fleet's governed speed. My first and second trucks were spec'ed during the 55mph Federal speed limit days. 1700 to do 70 mph killed my fuel mileage. I was trying to get the truck to do something it wasn't designed for.

 

Well, at the risk of being told I am crazy, what size tired do you have, 22.5 or 24.5, LP or high tread. Also open tread or closed shoulder tires, new tires with deep tread or older tires.

With a Detroit 12.7 with 22.5 LP you will get better mileage with 3.70 rears, and with 24.5 LP you will do better with 3.90 rears. I know this goes against everything people are being told today, but the older 12.7 engines like to be run at 1550 to 1650 rpms to make decent fuel mileage, as long as you're not geared too high and are doing over 70 at this RPM, which you are.

With your setup you are lugging the engine. The older 12.7 is dead in the water from 1450 rpm and under. I had two 11.1 Detroits at one time with 22.5 lp tires. One had 4.10 rears and the other 3.90. On roads with a 55 mph speed limit the truck with 4.10 rears would outperforme and get far better mileage than the 3.90. I also had a 12.7 with 3.70 rears and lp 22.5 tires. It would get it's best mileage at 67 mph. That was around 1650 rpms. Any slower or faster and you could see the mileage start dropping on the readout. I checked every fuel up with pen and paper from day one until I sold each truck, and know fure sure what speed and rpm worked the best.

I did loose some mileage one time when I bought a new open shoulder set of tires. It felt like I was running in sand. Also, Lucas in the trans or rears and engine at the levels they recommend will definitely loose you .5 to 1.0 mpg. I found out the hard way, and had new fluids in my rears and trans drained and replaced with factory weight, and started only putting about a quart per oil chance in the engine, none in the trans or rears, and my fuel mileage went up quite a bit. I wouldn't have put any in the engine but I had a lot of miles on it.

You can take this however you want, but I lived it, and kept meticulious records. And keep that cruise off when coming to a hill and pulling one. A good foot can outmileage a cruise anyday. Oh yes, do progressive shifting always. In low box just use enough fuel and rpm to get it moving before changing gears, then push the pedal like a raw egg is under your foot.

If the engine is in good shape you should see an improvement in mileage. The driver has a lot to do with mileage. I slip-seated for a couple years. The other driver got 5.7-6.0, and I got 6.75-7.20 doing the exact same loads. I also finished in the same amount of time as him. It's all in how you want to drive.

 

Stranger: I don't think your crazy at all. That "gear fast run slow" thinking has been taken to some great extremes with poor results. Yes the older S60 didn't have much below 1450 and had a real sweet spot somewhere above that.

My Mercedes actually gained 3/10ths when driving the same speed when I switched from 11/24.5 to LP24.5s. This is not something conventional wisdom would agree with or recommend. The extra 75 RPM also changed how/where the engine performed and gave me better drivability.