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6.2L/6.5L Tech Tech forum containing the best technical information about these engines. Please post in the related 6.2L & 6.5L forums. We'll transfer the best topic threads to this forum.

View Poll Results: Your 6.5 highway fuel milage?
less than 12 MPG 7 1.25%
12-13 MPG 28 4.98%
14-15 MPG 72 12.81%
16-17 MPG 133 23.67%
18-19 MPG 107 19.04%
20-21 MPG 64 11.39%
better than 21 MPG 49 8.72%
Just looking 102 18.15%
Voters: 562. You may not vote on this poll

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  #41  
Old 12-21-2007, 07:58 AM
acfloors acfloors is offline
Floor Guy
 
Join Date: Mar 2006
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Default fuel millage

I have a 2000 express 1 ton van with the 6.5L totally stock but for the K&N air filter. My best mileage to date was out west in nevada. I got just over 20 miles per gallon. I average 17 to 19 depending on if I run the cruise and keep it at or below 70mph.
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  #42  
Old 12-21-2007, 08:41 AM
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Robyn Robyn is offline
Missy Good Wench ( Moderator)
 
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My 95 3500 DaHooooley crew cab 4x4 with 6.5 and 4.10 gears will run 18-19 at 60-65 running light

Robyn
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(1) 1995 Suburban 2500 4x4
(1) 1997 Astro
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  #43  
Old 01-05-2009, 01:50 PM
gerritk gerritk is offline
gerritk
 
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Default Mileage

My numbers are like this:

1999 C2500 Suburban, 6.5TD with no engine mods of any kind, 3.42 rear in place of 4.10, 4l80e with no mods (but a deep cast aluminum pan), 23585R16E tires (Uniroyal Laredo cross country) at 65psi on stock steel wheels (245's are too small in diameter and too wide), 150,000 miles on odometer.

City 17.3 worst; 18.1 best (Houston area traffic)
Hwy 21.2 worst; 22.3 best (Texas Hill country to Flat Gulf Coast Interstate)

Keys I've found to mileage:
In the city: Gentle acceleration; as best you can, plan how you're going to make your stops in traffic (don't tailgate so you don't have to slam on the brakes).

On the highway: Cruise control at 65mph on the highway (about 1775 RPM on my rig).

Mighty happy with this from a land yacht:-)
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  #44  
Old 01-09-2009, 01:45 AM
motown motown is offline
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I'm going to pickup my new truck in dallas tx. here in a few weeks i'm driveing it home to frostburg md. its about 2000 mile drive it's a bonestock 1995 2500 ext.cab longbed 4x2 new motor exhast and tires i will post my results as soon as posible
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  #45  
Old 03-22-2009, 09:21 AM
motown motown is offline
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i got it home it didnt do bad the truck sat for 6 years with a blowed moter it had 83 miles on the new moter when i left tx. lift pump didnt work and the wastegate didnt work right still did prettygood on fuel
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  #46  
Old 06-27-2010, 10:11 PM
7thdaypope 7thdaypope is offline
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This is a great post from some real folks driving real trucks for real miles.

I am interested to know from those of you who have 3:42's under your rig if you have issues with lack of power especially while towing.

The gearing is great for mileage as we can clearly see from the posts, but can you pull a trailer up a hill without leaning forward in your seat?!

I'm deciding how to get the RPM's down under 2,000 on the highway, whether to change the gearing, or go to taller tires, or a combination of both.

Give me your input, what you have done, what you have seen or heard.
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1994 Suburban 2500. Bone stock 6.5T. 210,000mi.
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  #47  
Old 06-28-2010, 07:03 AM
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Quote:
Originally Posted by 7thdaypope View Post
I am interested to know from those of you who have 3:42's under your rig if you have issues with lack of power especially while towing.
I had a standard in mine and pulled a 2 horse trailer, about 5000 lbs. You had to work the gears a lot. It would have been better with an auto, although I doubt the mileage would have been as good. We saw 17+ mpg towing on reasonably level ground.

If I had been any heavier, I would have stuck with the 3.73 gears.
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Current oil burners: MB 350SDL, Kubota 7510
Gone but not forgotten: '87 F350 7.3, '93 C2500 6.5, '95 K2500 6.5, '06 K2500HD 6.6
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  #48  
Old 06-28-2010, 06:39 PM
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rustyk rustyk is offline
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I only have ~1,000 miles on it, but the Suncoast tranny rebuild, and its TC and input shaft, have apparently increased fuel economy from 10.5 to ~11.5 mpg.
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'94 Barth 28' Breakaway M/H ("StaRV II") diesel pusher: Spartan chassis, aluminum birdcage construction. Peninsular/AMG 6.5L TD (230HP), 18:1, Phazer, non-wastgated turbo, hi-pop injectors, 4L80E (Sun Coast TC & rebuild, M-H Pan), Dana 80 (M-H Cover), Fluidampr, EGT, trans temp, boost gage. Honda EV-4010 gaso genset, furnace, roof air, stove, microwave/convection, 2-dr. 3-way reefer. KVH R5SL Satellite. Cruises 2, sleeps 4, carries 6, and parties 8 (parties 12 - tested).

Stand-ins are an '02 Cadillac Escalade AWD 6.0L and an '06 Toyota Sienna Limited.
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  #49  
Old 06-29-2010, 11:06 AM
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Edahall Edahall is offline
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Quote:
Originally Posted by 7thdaypope View Post
This is a great post from some real folks driving real trucks for real miles.

I am interested to know from those of you who have 3:42's under your rig if you have issues with lack of power especially while towing.

The gearing is great for mileage as we can clearly see from the posts, but can you pull a trailer up a hill without leaning forward in your seat?!

I'm deciding how to get the RPM's down under 2,000 on the highway, whether to change the gearing, or go to taller tires, or a combination of both.

Give me your input, what you have done, what you have seen or heard.

My 1982 Suburban non turbocharged 6.2 has a 3:08 rear end and I tow a 26 ft airstream weighing close to 6k lbs. I'm using 30x9.50 15" tires. I tow in direct drive (3rd gear) and at 60 mph, the engine turns over at around 1900 rpms. It'll pull the smaller hills in direct drive but on steeper hills such as a 5% grade, once the speed goes under 45 mph, I shift to 2nd gear and then the engine puts out good power. I can pull as fast as 60 mph (3500 rpm) in 2nd gear if needed. I did some calculations and 3.08 gears with 15 in tires in direct drive is similar to 3.73's and 16 in tires in overdrive. Also, most transmission are the most efficient and can withstand the most torque while in direct drive.
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1990 ¾ ton 4x4 Chevy Suburban
-Cummins Diesel - 12 valve - factory rebuilt
-6 speed bullet proof manual transmission - NV5600
-Gear Vendors Overdrive
-Upgraded Holset HX-35 turbo
-NP205 iron transfer case
-3.73 gears

1982 ½ ton Chevy Suburban
-6.2L diesel - high nickle crack free 1982 block
-Stans headers
-Ported heads
-Timing gear
-4 speed automatic
-3.08 gears
-30 mpg on freeway
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  #50  
Old 07-17-2010, 08:27 PM
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rustyk rustyk is offline
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Quote:
Originally Posted by rustyk View Post
I only have ~1,000 miles on it, but the Suncoast tranny rebuild, and its TC and input shaft, have apparently increased fuel economy from 10.5 to ~11.5 mpg.

Now with 3K+ miles, about 800 in the mountains, mileage is ~11.7 mpg
__________________
'94 Barth 28' Breakaway M/H ("StaRV II") diesel pusher: Spartan chassis, aluminum birdcage construction. Peninsular/AMG 6.5L TD (230HP), 18:1, Phazer, non-wastgated turbo, hi-pop injectors, 4L80E (Sun Coast TC & rebuild, M-H Pan), Dana 80 (M-H Cover), Fluidampr, EGT, trans temp, boost gage. Honda EV-4010 gaso genset, furnace, roof air, stove, microwave/convection, 2-dr. 3-way reefer. KVH R5SL Satellite. Cruises 2, sleeps 4, carries 6, and parties 8 (parties 12 - tested).

Stand-ins are an '02 Cadillac Escalade AWD 6.0L and an '06 Toyota Sienna Limited.
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  #51  
Old 08-12-2010, 04:21 PM
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turbonator turbonator is offline
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Our 6.5L in the ''Pugg'' is getting just under 14mpg......(C-5000 truck)...LOL.
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  #52  
Old 10-05-2010, 02:03 PM
gerritk gerritk is offline
gerritk
 
Join Date: Mar 2008
Location: Houston
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Default

Quote:
Originally Posted by 7thdaypope View Post
This is a great post from some real folks driving real trucks for real miles.

I am interested to know from those of you who have 3:42's under your rig if you have issues with lack of power especially while towing.

The gearing is great for mileage as we can clearly see from the posts, but can you pull a trailer up a hill without leaning forward in your seat?!

I'm deciding how to get the RPM's down under 2,000 on the highway, whether to change the gearing, or go to taller tires, or a combination of both.

Give me your input, what you have done, what you have seen or heard.
I don't tow heavy very much but I did last weekend. It was all flat roads in south Louisiana towing a fully-loaded 6 X 12 U-Haul plus rooftop carrier plus a cabin full of people, probably around 5K lbs or so. The vehicle ran well and we had to cross a couple of large bridges over the Mississippi and Atchafalaya rivers. I was able to maintain 55 mph with about 65% engine load showing on my Garmin EcoRoute and about 185 degrees intake temperature going uphill (that's about all that will show on this setup). I don't have a gauge pod installed yet. If I were towing heavy loads all the time I'd want 3:73's, but the mileage with the tall tires and 3:42's running free is around 22-23 at 65 mph and that is how I usually travel. I also installed a set of rear disc brakes since my last post. They definitely stop a lot better. I didn't notice any change in the highway mileage but I did gain about 1 to 1-1/2 mpg in town, due to the lighter weight, I suspect. All-in-all we now have about 175,000 miles on our Sub and we absolutely love it.

A few weeks ago I made a trip out to San Angelo with it (no trailer) and ran 70-75 mph the whole way. I got about 19 mpg in the Texas Hill country at that speed and was never lacking for any passing power.
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  #53  
Old 01-31-2011, 12:55 AM
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Captain Jojo Captain Jojo is offline
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Default Best MPG to squeeze out

Hello,

Am getting 16 mpg at 63mph empty, with a 6.5 TD and 3.73 gearing in the back, 4L80e transmission and cutaway van with box (1 1/2 feet above cabin).

Got a couple of questions since I want to trim it to get as best of mpg on the highway at 65 mph as possible. Will not tow and run this van almost empty (will convert it to a RV):

Does anybody have experience at what rpm the engine runs with the 3.03 gearing of the rear axle instead of the 3.42, and if it still drives ok (not too sluggish)? What is the thinnest tire with the same outside diameter on this rig? I heard somebody using (harder) military tires for less rolling resistance and am wondering if that would be an option to consider. Am working on getting a wind diverter, too. What else can I do (IP is in good order)?

Thanks a bunch up-front. Am new to this croud here and must say that the abundance of info is overwhelming.
J
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2001 Chevy Van 3500 Express, no changes to factory, 6.5TD, 82k miles, USAF van until 77k. 4L80 tranny, 3.73 rear gearing, PMD relcated underneath the bumper.
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  #54  
Old 01-31-2011, 08:49 AM
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JohnC JohnC is offline
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I had 3.42 gears in my '93 and would not recommend going any higher than that unless you're putting it in a Corvette or something else really light.
__________________
"Need" - Wanting to get someone else's money.
"Greed" (formerly meant what "need" means today) - wanting to keep your own.
"Compassion" - a politician's willingness to arrange the transfer.
-Joseph Sobran

Current oil burners: MB 350SDL, Kubota 7510
Gone but not forgotten: '87 F350 7.3, '93 C2500 6.5, '95 K2500 6.5, '06 K2500HD 6.6
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  #55  
Old 01-31-2011, 11:56 AM
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Captain Jojo Captain Jojo is offline
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Well,

It is a express 3500 van with 5,500 pounds in weight, not necessarily the same category as a Crovette. However, I am not out to win acceleration contests but get good fuel mileage. Would the tranny suffer from such gearing? I am just trying to find out if the higher gearing to 3.43, such as 3.03, would be doable with a compromise in acceleration of it is just not practicable. Was wondering to mayby do 3.43 and experiment around with larger diameter tires...
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2001 Chevy Van 3500 Express, no changes to factory, 6.5TD, 82k miles, USAF van until 77k. 4L80 tranny, 3.73 rear gearing, PMD relcated underneath the bumper.

Last edited by Captain Jojo; 01-31-2011 at 02:28 PM.
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  #56  
Old 01-31-2011, 06:54 PM
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JohnC JohnC is offline
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Pick a speed, say 65 mph. Now, pick a gear ratio and tire size that puts you between 1800 and 2000 RPM. I think you'll find that 3.42 is going to be close to optimal unless you are grossing 10K or more. 3.03 is going to put you below the most efficient range, lugging if you will.
__________________
"Need" - Wanting to get someone else's money.
"Greed" (formerly meant what "need" means today) - wanting to keep your own.
"Compassion" - a politician's willingness to arrange the transfer.
-Joseph Sobran

Current oil burners: MB 350SDL, Kubota 7510
Gone but not forgotten: '87 F350 7.3, '93 C2500 6.5, '95 K2500 6.5, '06 K2500HD 6.6
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  #57  
Old 01-31-2011, 11:12 PM
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Captain Jojo Captain Jojo is offline
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Hey JohnC,

Am reading and learning. Thanks for your patience, am somewhat only getting started really getting to know cars and diesels in particular.
3.03 is going to put the engine below its torque peak, understood. I guess my question is still: what rpm would I land up with and how sluggish would that be? Still drivable in everyday driving conditions but just a bit slower acceleration, or almost no acceleration at 65? The fuel economy should be better below torque peak at 65, wouldn't it?

I assume you are saying that the gains in MPG would be too small to justify the compromise in acceleration? Or do I loose mpg because the overdrive wouldn't lock?

Thanks a bunch for your help, I appreciate it.
J
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  #58  
Old 06-10-2011, 03:40 PM
AKMark AKMark is offline
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My 99 Suburban, 4.10 gears, 115K with marine injectors.

Was getting 15 mpg with 245/75R16's.
Now getting 18 mpg with 285/75R16's. They just barely fit, but it sits nice and the BFG A/T rubber looks mean.

Both fuel mileage indications taken from my regular commute. 13 miles one way, till I hit 1/4 tank. 42 gallon tank. 55 mph speed limit, with the cruise set to 57-58 per GPS since the speedo is now off. 2K RPMS for 55 sucked with the little tires.
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85 K-5, 6.2, SM465, Rockwell T221, 1 tons, 36's. More goodies to be installed as time and money allows.
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  #59  
Old 06-24-2011, 06:53 PM
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argo argo is offline
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1 year update on the fuel economy for my Suburban: This is an aggregate average of a full year's worth of driving and fuel use. Since the conversion was completed, it has traveled 18,485 miles, consumed 740.258 Gallons of fuel, and averaged 24.971 MPG. This is overall MPG, with around town and highway. Best tank 28.1 MPG. Worst tank 17.7 MPG. I am very satisfied.
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1993 Suburban 2wd 6.2L Diesel Conversion "Andromeda":
3.73:1 gears, THM 700-R4 transmission, and
J-code 6.2L diesel from a 1984 C2500 Suburban

1996 2wd to 4wd converted Ford F-150 300ci Inline 6 "The Argo" 336,000 miles and climbing

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  #60  
Old 07-01-2011, 10:35 AM
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rustyk rustyk is offline
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Quote:
:
Originally Posted by rustyk
Well, I get about 9.3 mpg, but then my 6.5L TD is in an 18,000 lb. class A motorhome.

Things do change - with my replacement Peninsular Diesel AMG 230 HP (custom spec'ed) 6.5L TD, mileage is nearly 11 mpg...
Do a little here, do a little there...with the Suncoast HD tranny and TC, redoing the diffy (Someone had been in there previously and the pinion bearing clearance was way tight), and fixing a stuck caliper, consumption is now averaging 12.2 mpg over the last 5K miles.
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'94 Barth 28' Breakaway M/H ("StaRV II") diesel pusher: Spartan chassis, aluminum birdcage construction. Peninsular/AMG 6.5L TD (230HP), 18:1, Phazer, non-wastgated turbo, hi-pop injectors, 4L80E (Sun Coast TC & rebuild, M-H Pan), Dana 80 (M-H Cover), Fluidampr, EGT, trans temp, boost gage. Honda EV-4010 gaso genset, furnace, roof air, stove, microwave/convection, 2-dr. 3-way reefer. KVH R5SL Satellite. Cruises 2, sleeps 4, carries 6, and parties 8 (parties 12 - tested).

Stand-ins are an '02 Cadillac Escalade AWD 6.0L and an '06 Toyota Sienna Limited.
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