Actual, honest, real world MPG from your 6.5

[Acesneights1]

I don't know where everyone gets these #'s. I have owned a few 6.5TDs and they all were pretty consistent at about 15-16 mpg Highway. My burb gets about 15. It actually sucks.

 

[handcannon]

Also, try to drop boost to 3psi at your cruise speed. Guys with 4.10s might drive by the tach, sounds like you do for the most part, a speed where RPMs are close to 2000rpm.
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Buddy, could you explain how too much boost can affect fuel mileage? I'm having a rough time wrapping my head around that. How does boost change fuel consumption? Isn't fuel regulated by the IP and boost a byproduct of exhaust gasses? If you regulate the IP by the relationship of your foot to the go pedal and watching the tach how does excess boost mess with your MPG's? Aren't you just adding more air to an already measured amount of fuel?

My pickup is similar to Snowdrift's rig. 4.10 gears, 4L80E tranny, 2.65/75/16 tires, 4WD, turbomaster (PO added it), snorkle delete, 4" DE exhaust, stock tune. My winter MPG's from the end of Oct to the middle of April was 12.7 (winter blend?) and from there to my last tank was 14.1. Initially I wasn't being carefull about RPM's but have since been trying to stay below 2100 while at highway speeds. I know I've got gearing against me, but with others with 4.10s reporting higher MPG's I'm wondering.

Don

 

[ak diesel driver]

Boost comes at a price. To get boost you introduce backpressure into the exhaust system pre-turbo, Essentially making the engine work harder to overcome the backpressure.

 

[Woody35]

I don't know where everyone gets these #'s. I have owned a few 6.5TDs and they all were pretty consistent at about 15-16 mpg Highway. My burb gets about 15. It actually sucks.

if i drive like 80% of people out on the road and keeping up with traffic i only get 15 but if i slow down keep it under 2k rpms coast to stoplights etc... i can reach 17 mpg in the city. but once my turbo spools up my mileage goes down the toilet. same with highway driving. if i keep up with chicago traffic i only get 16 mpg because were traveling at 80 mph but if i stay in the right lane doing the speed limit i can get 20 plus with the 3.42 gears helping a lot.

 

[3500GMC]

So at 70mph taching 2500 my MPG will drop like a lead balloon...

Grrreat.

Regretting buying this truck. Damn 4.10 axles in a diesel light truck.......

 

[tanman_2006]

My 95 Z71 soot trap and muffer delete, K47, Vin F, 3.73's, 245/75 r16 mud tires, tuning by (staff edit) gets 19 cruising 70 and 18ish cruising 62 (wonder how fast i normally drive :hihi. I have a 6 setting tune with a stockISH setting and an econ setting, I get nearly the same mileage in both on the highway and better in town running stockish (17mpg around town). Both settings turn 5psi boost on the highway @ 70. My speedo is off but odometer is spot on. Towing on the highway I get ~16.5mpg grossing ~15K truck and trailer combo using (staff edit) towing tune (i didnt drive conservatively either).

My 93 flat bed is currently running factory exhaust (until 2mro when I but a Flowmaster DP and 3-4 foot of 3.5" pipe with a turn down which will cost me $40 total), IP cranked 3/8 turn, WG wired shut, 235/85R16 mud tires. Gets 16 highway and 14-15 in town. Speedo is right but havent checked the odometer yet. The tach reads ~2200 @ 65 which might be right with the larger tires. The IP is cranked awaiting the Holset swap which is on hold until I get a pay check (the front end on the truck drained the wallet), guages are in the seat just not installed.

 

[Crankme69]

X2 same here both my 6.5's have a (staff edit)/tune & I could not be happier...

 

[tanman_2006]

I feel good to get similar mpg as a 2wd . I got about the same highway MPG pre tune but it wasn't near as fun :hihi: .

I see 20+ on occassion but I haven't figured out what I did different to get it so IDK. :???:

 

[buddy]

Boost comes at a price. To get boost you introduce backpressure into the exhaust system pre-turbo, Essentially making the engine work harder to overcome the backpressure.

X2, boost is not only a function of waste heat. The engine must push harder to get the exhaust gasses into backpressure. The more boost, the more backpressure and its not linear, backpressure increases faster than boost. The more backpressure, the more exhaust gas is left in the cylinder for the next combustion cycle and less fresh air. The GMx turbo is fairly efficient at 2-3psi. A NA 6.5 would probably get 2-3 more MPG just by eliminating the restrictive passenger manifold and all the bends and extra pipe and small passages added because of the turbo.

 

[SnowDrift]

265/?R16 were on it when I bought it. Stockers may have been more anorexic - I'd have to look at the door tag again.

This morning, I verified 2050RPM @ 60 mph. About 3-4 psi at that speed on flat road.

EGTs dropped due to Heath's latest EPROM update. They dropped 50 degrees. They were consistently @ 450 when it was warm out and now they're at 400 under the same conditions.

 

[Acesneights1]

So at 70mph taching 2500 my MPG will drop like a lead balloon...

Grrreat.

Regretting buying this truck. Damn 4.10 axles in a diesel light truck.......

Yeah but a gasser under the same circumstances would probably get about 9-10. Exactly my point. People post #'s that they might have gotten on a straight HWY trip driving like Miss Daisy and those #s are deceiving..Like the Thread title says...POST REAL WORLD #'s ...

 

[chefmike]

Real world, I am driving mostly short distances and have hills both ways right now. Getting 13.7 every tank. I would love to take her on a trip and see what she does, but for the comfort and space and versatility, I am glad I have this truck. My Ford Ranger with the 4.0l got the same mileage here.

 

[handcannon]

X2, boost is not only a function of waste heat. The engine must push harder to get the exhaust gasses into backpressure. The more boost, the more backpressure and its not linear, backpressure increases faster than boost. The more backpressure, the more exhaust gas is left in the cylinder for the next combustion cycle and less fresh air. The GMx turbo is fairly efficient at 2-3psi. A NA 6.5 would probably get 2-3 more MPG just by eliminating the restrictive passenger manifold and all the bends and extra pipe and small passages added because of the turbo.

A great big THANKS to both of you AK and buddy. Your explanations really have helped me understand how boost and backpressure affect MPG. I'm going to see if changing the turbomaster setting and boost numbers can do anything to help my MPG.

Tanman, since you have some of (staff edit) tunes can you answer some questions? You say that the econ tune and stock tune get almost the same MPG. How do they compare/differ in other ways while highway driving? How about the tow tune? When I can scratch up the cash I want some of his tunes and an ATT and some real world info can really help me. I am running 4.10s and you have 3.73s so that may skew the comparison some but I still need info for decision making.

I like this thread. Some great info.

Thanks
Don

 

[buddy]

Some people do drive mostly highway, so it would be real world for them.

 

[Guster]

Fuel economy is slippery. Keep the EGT under 600, boost around 2 lbs or less. Fuel goes up with boost. Drag goes up geometrically with speed. 60mph or less gives the best mpg. Those mud tires or all terrain tires have huge rolling resistance numbers. Go with a highway tread (if possible)and and keep the tires inflated. I'm averaging 18 mpg local and 19.5 highway (at 70-75 mph).:thumbsup: And those are real numbers, not pencil whipped. I check every tank. My truck is bone stock, needs a set of injectors and an exhaust system.

 

[3500GMC]

My truck is bone stock, needs a set of injectors and an exhaust system.

Good numbers there. Curious to know what kind of animal you are talking about.. (fill out your signature in modest detail under the 'settings' tab top right of this page)

Welcome to TTS.

 

[treegump]

Just checked my mpg - 16.3 this past week. I try and check every week, and since I cut my CAT & muffler off, its improved by 1-3 mpg. I race to work, both highway, stop & go, and gravel roads (45-65mph), and cruise home with the same types of road (45-55mph). I go from a subdivision, through a college campus, onto a highway, to a gravel road, and this is with an empty bed, besides the 500lbs (guestimation) of tools that are in my crossover toolbox.

 

[chefmike]

You say that the econ tune and stock tune get almost the same MPG. How do they compare/differ in other ways while highway driving?

I have an econ tune and it makes the truck WAY more drivable. Around town, the truck seems more responsive in the lower RPM. I love my new shift points. It makes a big difference for me on the hills (holds better). Acceleration is smoother. The truck just feels all around more present, smoother. I would spend the money again in a heartbeat before returning to stock. And I have not gained MPG for my style of driving, but I gained a truck that I now love to drive.

 

[JeffMD]

I get fairly consistant 13.9mpg on B100. That is about 90% "city" driving and the remaining highway stuff is at about 70mph. Dino Diesel I do about 10% better (higher heat value will do that) On a road trip I can get the B100 up to about that and dino gets me 17-19 depending on speed. Such is life with 4.10 gears 6500 lbs and the aerodynamics of a brick

 

[Chief915]

Haven't had the suburban long, but here is what I have gotten so far....

1st tank was 75% city driving with a completely stock truck..... GM-4 turbo, factory wastegate, fender snorkle still there, and factory exhaust right down to the soot trap and factory muffler. I got 14.49 MPG over 566.5 miles.

2nd tank was 50% city.... GM-8 turbo, no fender snorkle, and new injectors.... I got 15.94 MPG over 513.2 miles.

I track every mile that goes on the truck and every drop that goes in the tank, so I will be back with more results.