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6.5 NA Mileage

Chevypoor

Chevypoor

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Location
Mineral, Va
Just bought a 95 1500 GMC reg. cab long box NA 6.5 diesel for a runner. What do they these things get for mileage? I thought I remember hearing they got around 21-24mpg. She has 3.42's with 235 75 r-15 tires.
 
Chevypoor said:
Just bought a 95 1500 GMC reg. cab long box NA 6.5 diesel for a runner. What do they these things get for mileage? I thought I remember hearing they got around 21-24mpg. She has 3.42's with 235 75 r-15 tires.
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22-25 highway should be obtainable if everything is in proper shape.

Under bumper air dam, small mirrors, maybe slightly lowered suspension, ht tires, and good alignment will do alot.

Might look into a tune to maybe adjust fueling at cruise and timing also delete the Egr using a military 6.2l lower or one ton civilian lower. Cat free high flow exhaust (3" is more than enough for NA).

Good injectors, pump timing, brakes that don't drag, good wheel bearings, and working lift pump all keep things as efficient as possible and are normal maintenance.

Source Unknown
 
Neighbor got his 86 Silverado with the 6.2 back on the road after sitting in the yard for many years and as far as I could tell it was 100% stock with ~85K miles. He was happy as anything as it got 27 mpg around town. Do not know if he still has the rig as he since moved.
 
JayTheCPA said:
Neighbor got his 86 Silverado with the 6.2 back on the road after sitting in the yard for many years and as far as I could tell it was 100% stock with ~85K miles. He was happy as anything as it got 27 mpg around town. Do not know if he still has the rig as he since moved.
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How do these people get this kind of mileage?
 
turbovanman said:
How do these people get this kind of mileage?
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In the Silverado's case, not a clue. Tires were definitely stock, so perhaps the rest of the story came from a 3.08 rear and speedo inaccuracy (guessing as to both). In the end, all I know is what I was told, and he was definitely happy with the burn rate. IIRC, CUCV Blazers can also get around this mileage.
 
JayTheCPA said:
In the Silverado's case, not a clue. Tires were definitely stock, so perhaps the rest of the story came from a 3.08 rear and speedo inaccuracy (guessing as to both). In the end, all I know is what I was told, and he was definitely happy with the burn rate. IIRC, CUCV Blazers can also get around this mileage.
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My 82 could break 30mpg. I only did it twice but I've also only filled one tank 5 times and saw 30 and 32 on 2 tanks. The truck is lowered on 15" rallys and wide 28" ht tires.

Source Unknown
 
2.73's... those are airplane gears. My wife had a 02 z28 with 2.73's. That LS motor did not hit its stride until 80!


Here are a couple pics. Ex VDOT truck with a cheap white paint job. I brought her home on the flat bed pulled by my other 95 today. Meant to get a photo of that but I forgot. Changed the oil and checked everything out. 130k on the the odo and somebody has removed the cat. It has 3" pipe from the y back and a flowmaster 40 series ( sounds good ) with a 2 3/4" tail pipe. Runs real smooth.

NA is the key to mileage from what I gather. These 6.5's NA are pretty rare. Believe they only made them for 2 years, 94 and 95. Sounds like 22-25 mpg is doable. This is my first NA diesel and I bought her for running payroll, carrying a couple of 2x4s, checking on jobs.... light duty stuff. I am currently running 4000 to 5000 miles a month on my other 95. It could use some occasional down time. Plus 25-30% better mileage will be nice for the bottom line.

Initial impressions are getting to speed requires patience and I imagine passing will be the same. Runs 70 on the interstate just fine. Handles hills at speed pretty good. So far I like it. If patience returns mileage than I will adapt. I have certainly driven alot slower and more gutless vehicles... just a little out of step with today's 300hp plus family cars and trucks.
 

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Looks slick. Orrum, our resident vegi oil traveler, did a ram air mod that he thinks helped. He had a few threads a year or so ago with a early 90's 6.2l,most threads are in the 6.2 area.

Egr is just an intake restriction when it comes to mpg. It might take a tune to get rid of the cel. Might as well see if tuning can aid mpg if you need it done.

Find a plastic valence for under the bumper, it's supposed to help divert turbulence from under the truck.

Source Unknown
 
I like my Vdot truck, thinking about buying another one and let my daughter have it for her first car, I just replaced the intake manifold with EGRless one from Leroy. I think it made a difference in mileage and performance. Nothing dramatic but if it gets to 60MPH a little better and one or two MPG more, its worth replacing. took me and my son a few hours to swap it out.
 
The air dam is my list of repairs as is removing the EGR. Plans are replace air dam, remove egr, remote mount PMD, oil lines, and Heath Chip.

Drago said:
I just replaced the intake manifold with EGRless one from Leroy
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Do you think he has another one he would sell me?:D
 
IMO the air intake plumbing is plenty good in the factory configuration, especially with the sunk back headlights of the WT grille. the scoop for the fender is right behind the headlight.

the non EGR intake is definitely a good idea.

synthetic oil in the rear end, air dam, good highway tread tires, etc. are all good places to start.

I love my little 91 GMC with the 6.2L. minus the electronic IP, I believe it is set up identical to the 6.5L NA trucks. mine can only manage 20-22, but I have EGR still working and a 4 spd manual with no OD. I think the electronic IP can get better MPG too.

I could rig it up with all the goodies, but I think with no AC from factory, I will just keep it pretty for local cruising and spend money on another truck with a/c and a NV4500. and also save money and try to find a 6.5L 5spd 2wd 94+ half ton.
 
Update: after almost 400 miles had to put some fuel and see what she was getting. I got 22.1 mpg with VDOT issue mud tires in the rear and no air dam. I currently get 18.2 - 18.9 with my 95 turbo diesel. Before the ladder rack and tool boxes in factory tune my 95 turbo diesel got 18.5 - 19.5. I once got 20.5. Not alot of extra mpg for alot less power.
 
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