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Actual, honest, real world MPG from your 6.5

I know nobody will believe some of this But I welcome anybody to ride along and see! most of our trucks get 18-23. But.....Dads 6.2 in his 72 with a 4-speed gets 25-28. And here is the crazy one!....I have the very tall 69 chev on 44" swampers and 4-speed and 4.10s. It gets 28....cool huh? Except when I am running on cooking oil! Then its 32! no joking or kidding or tall tale here! But Im sure that one will drop as that beast gets a twin turbo setup soon! Btw guys....someone said there is an area for the projects. I cant seem to find it. Would like to start posting on Dr.Evil.
 
Man my mileage is shit compared to a lot of you guys. What's wrong with my 1999 6.5td suburban?
I fill her up and I can only go 525 miles on a full 42 gallon tank. More about my trucks set up that I know of. Oh yeah only weight in her is me and my girl and together we weigh in at whooping 245 pounds... together!!

1999 6.5td 2500 Suburban 4x4 with custom 4" exhaust to 10" tip. Relocated PMD to front grill, PO stated she has a bully dog economy/Towing tune(yet I personally called bully dog to see if I can get her stock tuned again they don't even make a tuner for the 6.5! WTF?) PO also told me the transmission was beefed up for heavy duty equipment Towing. She's running 3.73 gears. She's sitting on 295/75/16's with shock extenders and leveling kit.
 
I'm thinking:

1. Disregard everything the previous owner told you. If he didn't get that right he probably didnt change the oil himself.

2. The tune that is in there may be an issue- the bully dog is probably an ebay special And can be creating an issue, along with whatever he may have had done to the trans.

These are wild guesses.
What turbo?
What boost?
If gated: vacuum, turbo master, or homemade spring from hell?
What injectors, how old, what pop pressures?
How fast are you getting up to freeway speed (0-60) under normal driving? Like old grandma or like me- foot to the floor.
How much of that 525 miles is freeway, and at what speed?
What air filter/intake?

All these things add up, some like turbo- more than others.

My under 9,000lbs hummer always got 10.5 mpg. Then I added turbo, added taller roof with piperack catching tons of wind resistance and weighed in at 10,000 lbs. and got the same mileage, but I sure went from back of the line to the front- way faster rig. Then started driving at old acceleration rate I used to and was hitting 12.5 mpg. I have an injector that isnt acting right, so I turned my fuel down to what would be stock td levels, and am driving softer. Now at just over 13 mpg. Ds4 pumps are way more sensitive to driving styles than db2.

Oh yeah, fuel used also. When I dump in a bunch of trans fluid or motor oil into the tank as fuel, that cuts it a chunk. Give it some good juice with only 5% bio and she likes it power and mpg wise.
 
Like Will said, if the PO doesn't know what tune is in it, he doesn't know anything else for sure either. I'd call Heath Diesel, explain that you bought the truck with a tune and are wondering if it's theirs. They can check your VIN to see if they sold one for that truck.
The 295 tires aren't helping MPG, I'd guess would drop it 1 to 1.5 mpg from what you'd get with 265/75-16's, particularly if they are A/T's rather than highway tread. Finally are you sure you have 3.73's? Wonder if you have 4.10's.
 
12.5 mpg. what are the rpm's at speeds? anything above 2000, cruising on a straight level highway, is a waste if looking for mileage.
 
My 6.5L averaged 15 MPG. On the highway I could just break 20 MPG. But my 3.42 gears helped a a lot along with new take off 265/70/R17's

IMG_20131008_104729_434_zps851fc8c5.jpg
 
I filled up before I went to Savanna GA to buy that hard top. So all highway driving I didn't go over 70 but mostly at 60 mph. At 70 mph my rpms are at 2. I know it's the stock Turbo. Don't know about injectors. Just know what I've done to her so far and it hasn't been much yet.
 
I have a 1994 K2500 extra cab pickup, 4.11 gears, auto trans, 265/75/16 tires, HX35w turbo, 4" diamond Eye exhaust, stock tune (I know a tune specific to the turbo would help some, but no funds for that yet). With the tire size and gearing I get 11 to 13 mpg on winter diesel, and 13 to 14 on summer blend. My tire size puts me almost exact at what the speedometer shows. By sticking strictly to the 2000 RPM limit, and all freeway driving, the best I have ever seen was 15.5 mpg. So, compared to what you have/get mpg wise 6.5TD.Club you are not any different than me. Your lift and oversize tires do not help your mpg at all. Instead, it probably cuts into your mpg.

Don

ps-2000 rpm is 60 mph for me.
 
Hey Don, i fell ya buddy. I don't even tow anything yet. I wanted the 6.5 diesel because it is supposed to get better mpg then the gasser. Guess I'm going to have to make some changes to her and see if I get better mpg.
 
6.5TD.Club, are you doing the math to account for your bigger tires? Assuming nobody did dip switches to account for them, your speedo and odometer are reading low because of fewer rotations per mile with larger tires. So your mpg would appear lower since it records fewer miles.
 
Well I got in touch with diesel addiction in Wilmington NC the shop who the PO told me tuned my rig so now waiting on the owner who tunes them to call me back.

Realistically can my 29's make that much of a difference? I've read through almost every post on the thread and there are other with lifts and bigger tires then mine getting better mileage then mine. I don't want to come off like I'm cheap about gas but I wanted a diesel Suburban for a reason. Better MPG, better for Towing, longevity of the engine if properly maintained.

I just feel like why pay more at the pump, pay more for maintenance, fuel additive, more for parts? I can save money by just driving a damn 350tbi or Vortec! I want my 16 mpg city and damn well 20 mpg highway for crying out loud! LOL
 
Have to get the details straight first, then know what to do. If you are running a gm4 turbo and craptacular tune- an ATT with a kojo tune and you ahould go up 2-3 mpg, and the extra power is free after the fuel savings gets it. Get some new bosch injectors from Leroy and stop at a shop to have them balanced out to within 25 psi of each other up to 2350 psi.
If it were an old tbi: you know new injectors inthe throttle body, new cap,rotor, plugs, wires, etc is all needed. Diesels just wants injectors and good airflow.
 
@6.5TD.Club

If you go A-Team Turbo for better mileage keep me in mind for your OEM turbo.

The joy of the automatic transmission is that even on stock fuel you can spool a big turbo with relative ease.

With my 5 speeds with the wide 3-4 gap, on stock fuel settings I need to stay with the stock GM turbos.

As far as the thread topic:
I think I responded earlier in this thread, but probably way back when the fleet was 2wd only.
My best all time is 22.5 mpg out of my 91 6.2L NA half ton, but that poor little gal is winding 3 grand to do 70. Thank goodness for the Fluidampr. :)

For the 6.5Ls, the 95 GMC C2500HD 6.5L 5spd 2wd with 4.10s has hit the all time high for my 6.5Ls at 21.5 mpg on a trip from Indiana back to KS. Trip out it was pulling a U-haul, and it got 14.5 mpg with the cruise on and the a/c on, even through the up and down Missouri hills.

Formerly my, now dads, 99 Chevy C3500 chassis cab 6.5L 5spd 2wd 4.10s hit 18.5 mpg on an empty run with no trailer once from Idaho to Kansas.

All I can muster out of my 4wds is mid to upper teens the few times I have ran empty. My latest 95 GMC K2500HD I think needs front wheel bearings and brakes, hopefully that will boost mpgs.

Towing is where 95-98 percent of my 6.5Ls miles come from, and they all get from 10.5-12 mpg towing, sometimes the weight can exceed 20,000 lbs combination on long trips.


I would recommend talking to the many happy A-Team Turbo owners on this forum, they all experience some sort of MPG boost over the GM turbo, how much was variable on the vehicle specs and the driver. I think the average is 1-3 mpg increase, with as low as .5 increase to as high as 4 mpg increase mentioned.
 
6.5TD.Club said:
Man my mileage is shit compared to a lot of you guys. What's wrong with my 1999 6.5td suburban?
I fill her up and I can only go 525 miles on a full 42 gallon tank. More about my trucks set up that I know of. Oh yeah only weight in her is me and my girl and together we weigh in at whooping 245 pounds... together!!

1999 6.5td 2500 Suburban 4x4 with custom 4" exhaust to 10" tip. Relocated PMD to front grill, PO stated she has a bully dog economy/Towing tune(yet I personally called bully dog to see if I can get her stock tuned again they don't even make a tuner for the 6.5! WTF?) PO also told me the transmission was beefed up for heavy duty equipment Towing. She's running 3.73 gears. She's sitting on 295/75/16's with shock extenders and leveling kit.
Click to expand...

Are you sure its a 42 gallon tank. My k3500 longbed only has a 34 gallon tank.
 
6.5TD.Club said:
View attachment 49255

I think this is the stock GMC Turbo.
Click to expand...

Yes that looks like a stock GM-8 by the spec tag.

The ATT and tune would be excellent for you. The only reason I ran a Holset is that it was given to me for some work I did.

Those tires are hurting you also. That's a darn wide tire! Get some nice stock newer take-offs (i personally love this type of look)
 
Best I've done is averaged 18 mpg pulling a 24' ultra light camper from Bethlehem Pennsylvania to Illinois with the 1998 K2500 Suburban - all stock at the time.

My 1994 K3500 averaged 18 mpg until I installed the ladder racks and tool boxes. Then it dropped to 15 - 16

The better mileages were also with the old diesel. Before they fixed it for emissions
 
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