Strange Fuel Mileage

[SquareDave]

I have a 2006 that I bought used. Fuel mileage in city driving is 19-20 per gallon. It would seem that highway driving would result in better mileage, but this vehicle does things just the opposite. I just got back from a 400-mile trip, and it dropped to less than 15 miles per gallon. I got better mileage when I had my old 1996 Chevy V-8. Does anyone have some notion as to what might be going on? I have suspected the problem for some time now, but I got around to doing a calculation this time, and its confirmation was even worse than I thought it might be.

 

[MChrist]

Are these hand calculated? That's the only way to be sure. My '06 gets between 13-15 in city driving (almost never getting into overdrive), and 19-20 on the highway at 65. I have hit 21. 3 at 60. This is with 3. 73 gears

I will assume you have 4. 10 gears. Do you have modifications? Big off road tires? Lift?

 

[Prairie Dog]

The overhead can wildly off.

 

[MChrist]

The overhead can wildly off.

This is why any/all discussions of mileage should never involve discussing what the Overhead-Lie-O-Meter has to say. Some readings are accurate, some are close, most are way off...
Only hand calculations should ever be mentioned.

 

[Bob4x4]

20 mpg city with an 06 4x4... ... ... . sounds like a dream

 

[SquareDave]

As far as I know, the only mod is the aftermarket muffler that was on the truck when I bought it. The rear end is 3. 73. There is no overhead lie-o-meter, so all my calculations are by hand. The in-town mileage has been consistently in the 18-20 range.

The daily commute involves a lot of "stop-go-stop-stop-park" on the I-35E and/or I-635 "parking lots. " I do road trips at speeds 65-85. The fuel mileage starts dropping around 55 mph with a drastic drop off between 65-70. The mileage falls of a cliff at 75.

My previous truck (2004) had good mileage throughout the whole range. I could depend on 600 miles with a filled tank whether in town or out in the wide open spaces - can't do that with this one. The performance of the current vehicle is good.

Possibilities that I've considered as a rank amateur:

1. Additional unknown mods by previous owner.
2. Valve lash adjustment (has 120,000 miles)
3. As yet undetected fuel leak at high speed.

 

[jgillott]

I may have missed it earlier in this thread, but is this truck in question a G56 or 48RE? I can tell you from experience that cruising at 75 mph is out of the question with an early G56 and 3. 73 gears. They simply are geared too low to achieve decent fuel mileage at that RPM over extended periods of time.

 

[SquareDave]

I may have missed it earlier in this thread, but is this truck in question a G56 or 48RE? I can tell you from experience that cruising at 75 mph is out of the question with an early G56 and 3. 73 gears. They simply are geared too low to achieve decent fuel mileage at that RPM over extended periods of time.

@jgillot: Your statement seems pretty consistent with what I have experienced with this truck, so I'm thinking you are onto something. The truck has the G56 (3. 73).

My former truck (2004) had the NV5600 and 4. 1, yet it still got better mileage at high sustained speeds than my 2006.

 

[jgillott]

@jgillot: Your statement seems pretty consistent with what I have experienced with this truck, so I'm thinking you are onto something. The truck has the G56 (3. 73).

My former truck (2004) had the NV5600 and 4. 1, yet it still got better mileage at high sustained speeds than my 2006.

It's going to feel painfully slow to you, but on your next trip, try running no faster than 65 mph. That should put you right around 2150 RPM in 6th. Your mileage should drastically improve. If it doesn't, then we can start looking for the cause of your low mpg.

 

[Wingate]

if you can consistently run 65 on 635 at quitting time. . I would consider you extremely lucky no matter what the fuel mileage is hahahahaha. . 635 is a friggin disaster

 

[SquareDave]

if you can consistently run 65 on 635 at quitting time. . I would consider you extremely lucky no matter what the fuel mileage is hahahahaha. . 635 is a friggin disaster

If I could consistently run FIFTEEN on 635 at quitting time I would consider myself extremely lucky. :-laf

 

[BIGNASTY]

I get 50 MPG BECAUSE I USE AMALGAMATED fuel additive. Dont believe me?



20 mpg city with an 06 4x4... ... ... . sounds like a dream IM MISSING SOME OF MY MED'S HAVE YOU BEEN HITTIG THE PAIN MED'S? :-laf



But it is possible IF you would use AMALGAMATED

 

[Bob4x4]

Even mileage numbers are bigger in Texas

 

[Regcabguy]

I'd love to get 20 mpg on the highway. I've had the camper off for a month now and the overhead's showing 17. 3 which probably is 16 mpg hand calculated. That's combined city/highway. The MT'

s cost me 1. 5 mpg. Odometer is only off by 1% thanks to Smarty and GPS verified.

 

[BIGNASTY]

Even mileage numbers are bigger in Texas

You better watch it BUDDY the HB hibernation in the Political Forum DEN is almost over and BIG MOMMA BEAR will be out and on the prowl for some new A** to CHEW. TOOK MY LEG OFF CLEAN UP TO THE KNEE JUST BY THINKIN ABOUT IT!!!!!!!! HE DID

 

[Bob4x4]

I might just fall off the couch after one more Beer

 

[BIGNASTY]

Want a BEER!!!!!!! I cant drink doing these MED'S if I did I would be saying NICE THINGS and that wouldnt be NASTY WOULD IT ?

 

[BIGNASTY]

Even mileage numbers are bigger in Texas

Want a BEER!!!!!!! I cant drink doing these MED'S if I did I would be saying NICE THINGS and that wouldnt be NASTY WOULD IT ?

You better watch it BUDDY the HB hibernation in the Political Forum DEN is almost over and BIG MOMMA BEAR will be out and on the prowl for some new A** to CHEW. TOOK MY LEG OFF CLEAN UP TO THE KNEE JUST BY THINKIN ABOUT IT!!!!!!!! HE DID

I might just fall off the couch after one more Beer

Would like to apologize for my failed attempt at A CHEAP LAUGH. Please attribute it to much pain for an extended amount of time and WAY TO MUCH PAIN MEDICATION. I will try to THINK before I type in the future.



SORRY HB



BIG

 

[SquareDave]

It's going to feel painfully slow to you, but on your next trip, try running no faster than 65 mph. That should put you right around 2150 RPM in 6th. Your mileage should drastically improve. If it doesn't, then we can start looking for the cause of your low mpg.

I ran the experiment going from Dallas to Shreveport this weekend and for the most part kept the speed under 65 and mostly right at 60 It is painfully slow, but with the price of diesel being what it is, my priorities are being adjusted. I got much better mileage this time around.