Trying to optimize my mpg/performance on/off road

[4 tone f250]

I had previously thought I had a 4.10 rear end but recently found out its a 3.54. I've got the 6.9 with the t19 4 speed 3.54 rear end and 315/75r16s. I get about 15-18 mpg. I'm now wondering if I got tires in the 33"range and somewhat narrower might I get better mileage or worse? If it turns out worse I'll be stuck with it for a while so I don't want to make that mistake, also I know its going to bring my hwy rpms up so I'm thinking it may cause me to burn more oil. So as a second part of the question does anyone know any oil that'll burn less. I got a hold of a couple gal of 30wt tractor oil a while back and that seemed to last longer than the usual 15-40 but I don't know how to get any more of it. Thanks in advance for your help

 

[rhkcommander]

15-18 is decent. im only getting 12.5 in city driving. i have a feeling my wheel bearings are shot and i do have a fuel leak at or past the IP. Filter stays primed so...

Narrower tires would likely help a little, rear end oil change to synthetic can increase mpg some too. A zf-5 and / or overdrive aux trans will help as the rpm will be lower at speeds. Free flowing exhaust and intake helps too. Keeping your foot off the skinny peddle and driving smart helps MPG a lot too.

Oil is an experiment you'll have to fiddle with, most say rotella burns up faster than say delo.

 

[4 tone f250]

Thanks when I said tractor oil I was actually talking bout like for farm equipment mostly I'm wondering if the shorter tires raising my rpms will hurt my mpg and if anyone knows if maybe a thicker oil that's not much more expensive

 

[Kevin 007]

Driving habits and injection timing seem to play the biggest role in IDI fuel economy.. I learned years ago to keep my foot out of the pedal and accelerate slowly and that makes a world of difference. Whenever you see black out the tail pipe...you may as well see $$$$ flowing out with it. So keep your foot out of it and make sure your pump timing is in the ball park. Too advance or too retarded will effect mileage no doubt.

 

[4 tone f250]

Kevin 007 looks like your 84 is probably almost the same set up as mine at least as far as running gear so what kinda mpg do you get and what size tires do you run?

 

[opusd2]

Driving habits make a HUGE difference. My 86 gets about 20mpg loaded or not, with 4.10s and c6. My tranny has been built to shift crisply, and I keep it between 50-55mpg all the time, even on the 65 mph roads. ****** people off, but works for me. Oh, and I have taller than stock 235/85-16s on and a few little mods.

 

[rpm427]

I read a story that if you took the HEAVY fan off motor the MPG was 2-3 more but of coarse you have to add electric fans.One guy said he took his off and didn't run any fan at all but I would say MAYBE but if so he wasn't doing any pulling with truck.The rear end oil change is ify as I understand the new trucks have the syn oil and they are having problems with the pinion bearings going out so you want feedback from people who have done the changes and will testify!

 

[opusd2]

Good Synthetic fluids don't cause problems. Bad bearing setup causes problems

 

[opusd2]

Or cheap bearings...

 

[rpm427]

If your working on a problem you either know what your talking about because you've worked on them or your rendering an opinion which is NOT the same but it has to do with the syn not having the same sticking properties from when you leave the truck sit.I've been told that the pinion bearings are going dry by the mechanics working on the problem!

 

[HammerDown]

From prior experience...a 'failing/bad bearing' lets you know.

 

[opusd2]

Sounds like top notch mechanics. (cough)

I've been selling synthetic oils fluids for the past 20+ years. I have absolute complete faith in them in anything with seals that actually seal. Even without good seals they lubricate better than conventional to much lower and much high temperatures without breaking down or slugging or coking up. A good synthetic coats bearings even if the remainder drains away.

Listen, believe whoever you want. It's your truck you are protecting. Just remember, at one point we used pig fat to lubricate wheels on buggies. If we never accepted a new way of thinking, well, oink.

I'm guilty of being stubborn and sticking to mechanically injected machines because I know how well ICBs handle heat and vibration loads without proper staking. All I am trying to say is, if you use good bearings not of Chinese import, set them up correctly, you can't blame the synthetic fluids. And if the component is of a poorly engineered design, which I have no idea if it is, then only the engineer gets the blame.

But like I said, make your own decisions. I'll make mine and continue to run my equipment into the 400K+ ranges as a couple of my rigs are.

 

[opusd2]

Oh yeah, with minor exceptions like in older vehicles which would leak them out, I have used synthetics exclusively for the past, well, since I started working for the oil jobber back in the early 90s. I got a sweet deal back then, so I bought only synthetic. Never looked back

 

[Kevin 007]

Kevin 007 looks like your 84 is probably almost the same set up as mine at least as far as running gear so what kinda mpg do you get and what size tires do you run?

Im running 285/75/R16 BFG all terrains, and im getting around 20+mpg. Works out to about 26ish mpg in Canadian gallons. Timing and driving habits play a big role also. I always let all the "hot rods" burn pass me leaving the light which is fine beause I will just pass them at the next gas station... And I limit myself to 55mph on the highway due to not having an overdrive

 

[4 tone f250]

Thanks for keeping this thread going guys I'm appreciating all the feedback and ideas and I think I'll try to get some narrower slightly shorter tires and probably when I can swing it a electric fan set up seems like a good idea to me my truck runs really cool so I figure it should be nothing but good