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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 05-20-2008, 06:41 AM   #1 (permalink)
knkreb
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***The Official MPG Thread*****

After getting about two or three threads, sometimes on the very first page it seems like about the question:

"What can I do about my MPG?"

With fuel prices over record breaking highs, we all are asking this same question. So I'd like to summarize for everyone some of the great ways that you can help to max out your MPG's.

1. Reduce cruising speed - running diesel engines at higher RPM's gobbles up more fuel than gasoline engines do.

2. Reduce idling. This too gobbles up more fuel than a gasoline engine will.

3. Fast accelleration - You have a lot of torque available at lower RPM's than a gasoline engine, but that torque comes from fuel. Getting hard into the go pedal will reduce your MPG's.

4. Rear gearing - not much most of us can do about this. 4.10 rear is great for get up and go and towing, but reduces fuel milage. 3.73 is better, 3.42 is really good for fuel, but reduces the capacity of towing capabilities.

5. Clean air filter

6. Injectors - injectors "wear" - or lose some of there optimium settings and spray abilities over time. If injectors are going out of spec, you *could* be losing some engine efficiency.

7. Tire pressure - full spec on your pressure helps.



A note on fuel milage measurement. If you don't top off your tank to the fullest, your numbers will tend to drift one way or another. It's best to be as scientific about things as possible when making your measurements. Also, don't take one tank as "in stone" measurements. Average them over the next few tanks.


This thread is open for everyone to contribute to.

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*Currently driving an "Canadian Camo" Snow White 2001 5.7L Chevy Express.
*Bus 2, 99 7.3L PSD.

Last edited by knkreb; 05-20-2008 at 06:45 AM.
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Old 05-20-2008, 07:58 AM   #2 (permalink)
acesneights1
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I gained 1 mpg by gutting kitty, mandrel bent crossover and downpipe and 4 inch out from empty cat back. Free flowing exhaust helps a little IMO.

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Old 05-20-2008, 08:59 AM   #3 (permalink)
gonnasellit
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1. Be sure your thermostat is the correct one to keep coolant temp at least 180 - 190degf.

2. Reduce weight by removing any unnecessary weight in the truck that you don't need.

3. If driving an automatic try to get to up to speed where TCC is locked and in high gear fairly quickly (without dogging it).

4. Turn off A/c when not needed.

5. Use synthetic fluids in the engine, tranny and differential.

6. Don't drive with the tailgate down. This has proven to decrease mileage. A tonneau cover increases mileage on highway, but probably decreases mileage if most of your driving is in town or at slower speeds due to the estra weight.

7. Don't use tires with aggressive tread (ie mudgrips) unless you need them. Highway tires get better fuel mileage.

8. When pulling a trailer, try to keep load as low as possible to reduce drag.
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Last edited by gonnasellit; 05-20-2008 at 09:12 AM. Reason: Additions
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Old 05-20-2008, 06:34 PM   #4 (permalink)
instarx
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About 18 months ago I asked members about their best fuel saving tips. There were were about 30 great tips that hold true today:

https://www.dieselplace.com/forum/showthread.php?t=97786
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  • 100% Fossil-Fuel free with B100, 15/17 MPG
  • Years of trouble-free B100 use: 1.8
  • Currently not running due to broken connecting rod
"New" vehicle - 2000 Volvo V70 AWD turbo wagon (gas) - owned six months and I STILL wait for the glow plugs!

Last edited by instarx; 05-20-2008 at 06:39 PM.
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Old 05-20-2008, 06:55 PM   #5 (permalink)
Kartoon
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I know this is a given, but check for fuel leaks. I had one and after I fixed it, my mileage jumped. Check under the fuel filter for any small leak, if there is fuel there, fix it, no sense in putting $5 gallon diesel on the pavement.
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Old 05-20-2008, 07:38 PM   #6 (permalink)
adamguy2006
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Quote:
Originally Posted by McRat
I heard a Tornado, K&N, and some acetone in the tank will double your fuel mileage.



If you recalibrate the speedo 2:1...
I installed the factory replacement style K&N air filter in my Dmax and I picked up 1.5 MPG. The acetone does work we tryed it our PowerJoke (7.3) and it picked up 2 MPG (over 10% increse) (fuel lubertcant recomended). The tornado on the other hand is a joke anything in the air stream to "change direction" of the air is only a restriction like a dirty air filter. We have tested this at my college (it reduced fule economy).

Quote from the linked thread.
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Old 05-20-2008, 10:17 PM   #7 (permalink)
knkreb
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Please note folks that acetone is NOT a recommended additive to your fuel system, damage will occur to it's components!
__________________
Look here-> GM 6.5 Reference Material & FAQ's <-Look here

Diagnostic Links & Common Failures: Turbo System * Lift Pump/OPS * PMD * Stalling


°Please include your vehicle details in your signature line. Did you read the FAQ's and search before posting?
*Bus 1, rest in peace. Bone stock, now just bones. 4.10 rear 10/13 mpg, 182,000 miles with a set of MCI motor coach seats.
*Currently driving an "Canadian Camo" Snow White 2001 5.7L Chevy Express.
*Bus 2, 99 7.3L PSD.
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Old 05-21-2008, 06:19 AM   #8 (permalink)
instarx
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I think the title of the thread should be "Fuel Saving", not "How to get better MPG." No matter what MPG you get, if you have 20% more fuel in your tank at the end of the week you've saved 20%.

Here are some ideas for saving fuel that can lower your GPM (gallons per month). I've guestimated each one on a 10-point scale with 1 being the least savings and 10 the most savings.
  • Don't use M&S tires all year round. (+7)
  • Don't carry around unnecessary weight (+2)
  • Never use your brakes. Keep your truck moving as much as possible. (Notice how much you are pushed forward when you brake and then imagine how much fuel it will take to press you back in the seat that same amount. That's exactly how much fuel you will need to re-accelerate your truck.) (+6)
  • Use your GPS to plot the most efficient order to make multiple stops. This can save huge amounts of distance and fuel. (+7)
  • Use your GPS to plot the shortest route. Even half a mile saved in a 5 mile trip is a 10% savings! (+7)
  • Don't keep your tank full - keep it half full. Fifty gallons of fuel weighs 400 lbs. Be careful - because you have to visit gas stations more often see next point. (+1)
  • Don't drive TO a gas station - stop off at one you are driving past. If you make a special trip to a station 5 miles away the extra fuel you use is the equivalent of paying an extra 5-7 cents per gallon, depending on your mileage! (+2)
  • Use the appropriate vehicle. If you don't need the truck don't take it. If you have a car always use the most efficient vehicle for the job. You don't need a 6,000 lb truck to pick up a loaf of bread - you do need it for a load of gravel.(+5)
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1995 G30 1-ton van, 6.5L non-turbo; 150,000 miles. Seats In: 15-passenger van. Seats Out: mobile bowling alley
  • 100% Fossil-Fuel free with B100, 15/17 MPG
  • Years of trouble-free B100 use: 1.8
  • Currently not running due to broken connecting rod
"New" vehicle - 2000 Volvo V70 AWD turbo wagon (gas) - owned six months and I STILL wait for the glow plugs!

Last edited by instarx; 05-21-2008 at 06:46 AM.
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Old 05-24-2008, 12:07 PM   #9 (permalink)
fasteddie1_2003
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fuel mpg

take a look at those auxillary units for overdrive and underdrive i've heard alot about people saving fuel with those but i've personally never tried them another thing i've seen is the kits that they are selling that make hydrogen out of water they advertise 30 to 70 % increase in fuel mileage but i don't know i've never tried them.
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Old 05-25-2008, 09:05 PM   #10 (permalink)
cretan
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Quote:
acetone?
cetane to increase mileage mabey.I just took my N/A for a trip and got 28 MPG(canadian gallon)or 23.5 mpg(US).With a slight tail wind.17 city driving.TDCO at -.70 engine at 1750 RPM doing 104 KM per hour.With my other truck which is a turbo if I keep it under 100 kph it gets 24 mpg(can)As soon as I go over that mileage suffers. Check to make sure there is no drag in the braking system,e-brake ect.Have not tried it but some say highway driving with the tailgate down also helps mileage.

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