Question: 6.5TD best Fuel economy? How can we get 21mpg+ ? (is it possible??) - Page 4 - Diesel Place : Chevrolet and GMC Diesel Truck Forums
 
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6.5L Diesel Engine Discuss the 6.5 GM diesel engine & associated components. Automatic transmission questions & problems belong in the 4L80/85 - 4L60E - 6L90 Transmission Forum

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Old 01-13-2015, 07:00 PM   #31 (permalink)
jdf915
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We get about 13-15 mpg out of our 95 3500 6.5 non working turbo and that's at about 3k rpms.

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95 chevy 3500 extra cab ds4 ip
80 chevy C30 standard cab city owned for 34 yrs
true duels and headers
Check out my build thread C30 build
1997 land rover disco I, going to be 6.2
2" lift black rims over sized tires, fuel mileage is rumored at 26-28 MPG
here's the build thread Land Rover Build
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Quote:
Originally Posted by 90GMC62L View Post
I wish skinny tires didn't look so lame.
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Originally Posted by Bigboytoys View Post
And that isn't your every day talent there....
list of db2 pumps and applications. Pump INFO Here's some thing else that's interesting.Gauge Pod
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Old 01-13-2015, 07:02 PM   #32 (permalink)
jdf915
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Quote:
Originally Posted by jdf915 View Post
We get about 13-15 mpg out of our 95 3500 6.5 non working turbo and that's at about 3k rpms.
That's with 4.10 gears. Want to put 3.73 or 3.42 gears in it.

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95 chevy 3500 extra cab ds4 ip
80 chevy C30 standard cab city owned for 34 yrs
true duels and headers
Check out my build thread C30 build
1997 land rover disco I, going to be 6.2
2" lift black rims over sized tires, fuel mileage is rumored at 26-28 MPG
here's the build thread Land Rover Build
MEMBER #1072 of the dually club
Quote:
Originally Posted by 90GMC62L View Post
I wish skinny tires didn't look so lame.
Quote:
Originally Posted by Bigboytoys View Post
And that isn't your every day talent there....
list of db2 pumps and applications. Pump INFO Here's some thing else that's interesting.Gauge Pod
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Old 01-14-2015, 08:20 AM   #33 (permalink)
guybb3
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Quote:
Originally Posted by DieselPower5 View Post
Winter Diesel will really lower the MPG, yiks, why is that, less Cetane?
1. stock boost, 3lbs and a 1
No parafin in winter fuel. That is the "gelling" we experience which is really parafin dropping out of suspension. Parafin = fuel so less parafin = less power + less fuel economy.

Things I have done to my Burb to up the mileage

60 PSI in my 235/85-16 tires
non-wastegated *** turbo
new exhaust system
all synthetics
alloy wheels
rear wheel disc (must have saved 80 lbs of rotating mass)
3.42 gears (came with truck)

to come

electric fan (my towing isn't that heavy and is done at 65 mph)
air dam extension on front
removing roof rack
new tune
new injectors with higher pop pressure
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Last edited by guybb3; 01-14-2015 at 08:20 AM.
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Old 01-14-2015, 03:19 PM   #34 (permalink)
paleyjim
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Ive been trying to squeeze more mileage out of my 6.5. Ive pretty much tracked mileage since I got the truck along with any changes Ive made. Here is my history:

Jan 2012 into Summer: Purchased the truck in January. My mileage started out at about 13.5 MPG in January with mixed driving. As the temp warmed up in summer, I hit 15-16 MPG on some trips. Changing a bad wastegate solenoid in April (causing low boost) seemed to make a small improvement in mileage (0.2 0.3 MPG), though it is difficult to tell for sure with an increase that small. Engine oil and rear diff oil were changed to synthetic, but I could not see any difference in mileage.

Fall 2012: Got an unknown quantity of fuel oil that lasted most of the fall. I was not able to track mileage.

Winter 2012/2013: Mileage dropped back to 13-14 MPG. K47 airbox was installed. #9 resistor was installed. TDCO was adjusted to -1.76. None of these significantly changed mileage for the good or bad.

Summer 2013: 15-16 MPG. No changes to the truck.

Winter 2013/2014: 13-14 MPG until a new set of 265/75-16 MTs were installed which dropped me to my worst mileage ever 12-13 MPG. Injectors were changed early spring and did not make any measurable difference in mileage.

Summer 2014: 4 downpipe back exhaust installed at the beginning of summer. The 6 fillups before the exhaust was installed averaged 13.2 MPG. The 8 fillups after the exhaust was installed averaged 14.4 MPG. Exhaust gained me about 1.2 MPG however this was still significantly worse than previous summers. In August I swapped on a set of very non-aggressive AT tires (265/75-16s still almost a highway tread). Mileage averaged 17.1 MPG for the next 5 fillups. This is a 2.7 MPG improvement just from swapping tires. Seems ridiculous.

This winter: Tires swapped back to MTs for winter use and air filter was replaced. Mileage has varied from 13.61 to 15.11. Im not sure why mileage has not dropped as low as other winters even though the MT tires seem to be fuel hogs. I suspect the exhaust is helping, but I suspected that would be more than offset by the tires.

My long term goal is to see 20 MPG with this truck. Not sure if this will ever happen, but Im allowed to dream right?

In summary:
-In the winter I tend to see 13 to 14 MPG
-In the summer I see 15 to 16 MPG.
-Things that have influenced mileage:
* correcting a boost pressure problem
* installing a 4 downpipe back exhaust
* switching tires (MTs = bad mileage)
- Things that have not measurably changed mileage:
* synthetic fluids
* injectors
* #9 resistor
* TDCO adjustment
* K47 airbox
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Old 01-14-2015, 04:24 PM   #35 (permalink)
90GMC62L
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Jim your experience sounds exactly like mine. I average about 12.5-13.5 in the winter and 15.5-17 in the summer. I just put on 285/75 tires a few months ago so i'm curious what i'll get once summer fuel comes around again. My old tires were 235/85s. Seems like I got about the same as I do now but it's hard to say. I wish skinny tires didn't look so lame otherwise i'd still run them.
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Old 01-14-2015, 04:53 PM   #36 (permalink)
jdf915
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Quote:
Originally Posted by 90GMC62L View Post
I wish skinny tires didn't look so lame.
Amen brother!
__________________
95 chevy 3500 extra cab ds4 ip
80 chevy C30 standard cab city owned for 34 yrs
true duels and headers
Check out my build thread C30 build
1997 land rover disco I, going to be 6.2
2" lift black rims over sized tires, fuel mileage is rumored at 26-28 MPG
here's the build thread Land Rover Build
MEMBER #1072 of the dually club
Quote:
Originally Posted by 90GMC62L View Post
I wish skinny tires didn't look so lame.
Quote:
Originally Posted by Bigboytoys View Post
And that isn't your every day talent there....
list of db2 pumps and applications. Pump INFO Here's some thing else that's interesting.Gauge Pod
Offline   Reply With Quote Quick reply to this message
Old 01-24-2015, 07:46 PM   #37 (permalink)
EVguitarZ
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I'm in the 12-13 winter and 15-16 in the summer. This is with a square tube ladder rack and a few hundred extra pounds of bumpers, fuel tanks, and camper shell, and D rated 315-75-16s (hanook dynapro). It was better (like 17-18 on the highway) before all the add-ons. I'm pretty light on the pedal though.

I have achieved the 25+ in a GM diesel in the past. It was a single cab 1985, 1/2 ton 6.2 NA with 4.10 gears and a 3 speed with granny. 245/75/16 tires, and it wined like crazy over 65mph, so I never went over that. Once I put (light weight) slide in camper in it went down to 17 or so. A few months before I sold it i swaped to 3:42 gears since I was doing lots of higway driving; I was able to go a bit faster, but my combined mileage went down to 19-20 combined in the summer rather than the 23-26 before.

One thing that I don't know if anyone's mentioned yet is how much engine warm up effects MPG. Last winter when it was in the single digits I was making lots of 1-2 mile trips in my truck and got about 8MPG on that tank.
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Last edited by EVguitarZ; 01-24-2015 at 07:46 PM.
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Old 01-24-2015, 08:07 PM   #38 (permalink)
Franswa
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I was spending $90 a week on my 1500 5.3 silverado to work, that was with higher gas prices, but im spending $40 with the higher price of diesel for 250 a week, it's mainly why i bought the green monster. Just haven't sacked up and filled the 42 gallon tank for actual mpg yet, but my butt calculator again says 20
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Old 01-24-2015, 09:42 PM   #39 (permalink)
VanBoy
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I was thinking, how much did the sulfur in the diesel play in fuel economy? Did it any? Some said the old 7.3L PS in the Fords could get up there when there was sulfur in the diesel...after it was reduced, some say it went down and by a bit.

If this is true, I'm sure the 6.2 & 6.5 dropped too when sulfur was removed......
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Old 01-25-2015, 09:42 AM   #40 (permalink)
IamDave0887
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I'm getting 22 mpg out of my 6.2T K-5 with 3.08 gears, 33x12.50x15 tires, and a SM465 non-OD trans.

Spinning 1,900 RPM at 65 MPH.

I've seen as high as 24 MPG highway on a 5+ hour highway trip with my pickup before, and that's 3.73 gears, 245/75/16 tires, and a 4L80E trans. 2WD though so that helps.

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