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fuel economy, who has the best?

devildogadam

devildogadam

Active Member
Messages
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Location
Yakima WA
I want to know who is getting what in the mpg department. I recently started a thread on a liberty forum kind of bashing my liberty for getting sick poor economy. And got a lot of flack for saying it should do better. And I dawned on me. My first Chevy diesel was a 1991 k2500 na 6.2 with auto Trans and that still got around 22 mpgs on the highway and about 19-20 around town. So what is everyone else getting. Who has the best/worse and if you have the best. What setup are you running. My current truck gets about 17 mpg but I am not nice to it plus it has 4.10 gears.


Admin: feel free to move this thread where ever you feel it belongs.
 
19.5-20.5 highway. 18 around town. Both are empty truck stats. 3.73 with 265s on rims. I have no idea how to adjust for bigger street all terrain tires. Its about 3 miles an hour off on the slow side according to gps. Read sig for upgrades, ATT got me the most mileage gains. Used to get 17.9 with GMx on highway.
 
Usually 18 combined. Can get down to 15 combined in winter due to fuel enrichment cycle, slippery conditions, cold running and warm up cycles.

ECLB, fiberglass bed cap, 265 tires, PYO rims, 4:10 final gearing, 4L80E, pushbutton 4x4. Usually running 6800-7000 gvw.

Could probably eep out a few more if I played with the calibration enough, but I'd likely be giving up some power for it.

Im happy "as is" with lots of throttle reserve and 15/18 mpg from a 3/4 ton 4x4.
 
Im running 35'' tires and 4.56 gears. Around town I get 14-16 (I'm heavy on the throttle :D) the freeway isn't much better. I have 100k on the injectors and a set sitting in the garage, hoping to regain some mileage with them, and will be testing out an ATT on my truck in place of the Holset. Hope to see some mileage gains with that as my cruising boost is a little high.
 
Don't think I qualify for best mileage... After adding the turbo, turning up db2 fuel screw a bit more than a half turn, and replacing injectors with factory turbo injectors that had about 70,000 miles on them: My mileage went up from 10.4 to 12.4 mpg. If I would turn the screw back down just a hair (20 degrees or so) I could pull out about 13 mpg. Keep in mind my aerodynamics, and I am never under 9,000 lbs, usually 9,500.
 
Got in the 19 territory with the nearly blown motor and (did not know it at the time) nearly blown 4L80E.

Too early to tell how the P-400 is doing as I am still breaking it in.


If you really want to push the envelope for fuel mileage, switch the viscous fan clutch for either a Horton electric or Hummer hydraulic clutch. IMO, either of these options will need a pusher fan which triggers from the A/C.

IIRC, read a report of a Burb (GMT400 body) that got 27 mpg highway (while using A/C) by switching the fan over to an electric from an Olds. If you are not going to tow, the Flex-A-Lite looks like a good solution.
 
JayTheCPA said:
Got in the 19 territory with the nearly blown motor and (did not know it at the time) nearly blown 4L80E.

Too early to tell how the P-400 is doing as I am still breaking it in.


If you really want to push the envelope for fuel mileage, switch the viscous fan clutch for either a Horton electric or Hummer hydraulic clutch. IMO, either of these options will need a pusher fan which triggers from the A/C.

IIRC, read a report of a Burb (GMT400 body) that got 27 mpg highway (while using A/C) by switching the fan over to an electric from an Olds. If you are not going to tow, the Flex-A-Lite looks like a good solution.
Click to expand...

Im running the dual Flex-a-lite and love it. I felt a noticeable power increase with the old fan off and during the summer here the truck stays nice and cool :cool:. I have also had good luck towing with the fans too, but I don't tow as much as a lot of the members here.
 
I got ya all beat: 7 MPG towing. :D I don't think it's possible to go lower while moving. (A gas engine is cheaper to operate towing even at it's 6 MPG vs. a stock 6.5.)

Then after improvements gained 3.4 MPG and like 25MPH towing. ATT, 4" exhaust, Walbro lift pump, snorkel removal.

Best at freeway speeds was the suburban with the ATT and spool valve getting ~16 MPG at high CA freeway speeds - an improvement over 14 MPG. Round town I get 10 MPG.

The 2003 Dodge 5.9 with the MT is 20 MPG mixed with a big hit to 16 MPG AC on. It goes over 20 MPG freeway. ~15 MPG towing.

Keep in mind LSD and ULSD is lower BTU diesel than the fuel of the past. So MPG you recall from the past is no longer possible on today's fuel. Biodiesel (B99) also reduces MPG by 10% due to less BTU.
 
devildogadam said:
What the heck where you towing to get that low?
Click to expand...

This on grades from 7% to 18% that go for miles in hot weather up to 121 degrees. Back story to it here.

28trailer.jpg


Light load as this could be filled to the ceiling: (Yes I did bend the hitch and frame around the hitch by overloading the tongue via unloading the rear of the trailer then going across town to unload the rest on a Vegas run one time.)

trailertires.jpg

Yes, this is a real high wind resistance trailer not wimpy low profile logs GM tests with.
.
 
I've never actually checked mileage with a load of brick or what not. Don't know, don't wanna know. Its around 9ish though. The fact the truck does its job when pressed is all that matters.
 
Even loaded down with our 35 foot 9,000lb travel trailer and going over places like vantage, lookout, 4th of July and in and out of Butte I never dropped below 12-13 mpg....
 
It was written back in the day when different better turbo's for the 6.5 wasn't common knowledge.

GW:
It more extreme than Montana. Not to take away from The Rocky Mountains as they are indeed a bunch of good grades, but, AZ is kinda like Wyoming hilly all over. (Hilly is Wyoming but an understatement for AZ.) I am only seeing 5000' or lower elevations where you went and possibly freeway at that. Freeways limit grade %. The route I was running is a turbo creep inducing 7600' and constant up and down extreme grades. ( Google a terrain map of GPS 34.300910, -110.902726 ) The elevation reached and then went over the limit of what the GM turbos can handle smoking bad even with a DB2 pump. (Had to turn the fuel down.) AC usually on as needed but possibly turned off in higher elevations. Outside air temp is higher and elevation both derate engine power and reduce MPG. Used several vehicles and all were horrible MPG as noted. Even other driver's Duramax or Cummins was in the 11 MPG range.

People complain about maxing out their unloaded vehicles on these climbs. Many burn marks on the side of the roads where stuff simply burns to the ground. Denver, Colorado going west may give you an idea of a good climb.

Now if I went West from Phoenix to Lake Havasu City my MPG would be better around 11 MPG in the 1993 if I recall. But speed limit is 75 and best it had flat out was 62 MPH with the GM3.

No doubt the extreme extended WOT pulls on these grades has tainted my perspective. For sure it's blown up a lot of parts in a hot oily mess. With that I have learned how to get reliable power out of the 6.5. Not that I had a choice to get something else at the time - I didn't.
 
For my truck in the signature, you can see all mods I have.
For mixed driving I average 14
For full freeway driving 18
Towing 11

I track all my fuel stops and maintenance on an APP on my phone. My numbers are all over the place so, the numbers above are my average.
 
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