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Old 08-14-2005, 07:54 PM   #1
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Fuel economy ideas and MPG Boosting (merged threads)

We drive an '04 Silverado 2500 Duramax, purchased March, '04. It has about 21,000 miles on it. Pulling the 30' Airstream earlier this summer, it was getting 12-14 mpg. Max ususally drove in the 70-75 mph range. (Personally, I think that is too fast, giving less reaction time for unexpecteds, but that is another thread, another time.) Lately, I proposed limiting our speed in the truck to 60, max. I believe I've read on this forum that 55-60 gives optimal gas mileage. Checking, it looks like we are now getting 17-19 mpg at the reduced speed on the highway, not pulling, and including town start and stop drives as well. My question: is this realistic gas mileage for our truck with its current miles? What are other methods for improving gas mileage? I really thought it would be better by now with the diesel. Discussion and suggestions are appreciated-especially at the $2.49 pump price we are seeing here.
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Old 08-14-2005, 08:25 PM   #2
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Quote:
Originally Posted by maxandgeorgia
We drive an '04 Silverado 2500 Duramax, purchased March, '04. It has about 21,000 miles on it. Pulling the 30' Airstream earlier this summer, it was getting 12-14 mpg. Max ususally drove in the 70-75 mph range. (Personally, I think that is too fast, giving less reaction time for unexpecteds, but that is another thread, another time.) Lately, I proposed limiting our speed in the truck to 60, max. I believe I've read on this forum that 55-60 gives optimal gas mileage. Checking, it looks like we are now getting 17-19 mpg at the reduced speed on the highway, not pulling, and including town start and stop drives as well. My question: is this realistic gas mileage for our truck with its current miles? What are other methods for improving gas mileage? I really thought it would be better by now with the diesel. Discussion and suggestions are appreciated-especially at the $2.49 pump price we are seeing here.
Keeping your tires inflated to the proper amount will also help, as will leaving all your tools and boxes of "stuff" under and behind the seats at home, instead of in the truck. Keeping the bed empty will also help, as will a tonneu cover or a bed cap, or topper.
Avoid idling for extended periods, even with the diesel, and keep your oil and your air filter changed regularly. The actual best speed for improved gas milage is 50, after extensive testing in the early 1970's. IIRC, fuel consumption increases by 5% per mile per hour over 50. Of course, if you tried driving 50 today, you would get run off the road, or worse.
I tried this with our van, it gets 9.8 mpg towing the Overlander at 65, 10.5 at 60, and 11mpg between 55 and 60.
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Old 08-14-2005, 08:59 PM   #3
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I've seen progressive improvements in my MPG in the Motorhome as I've either repaired or replaced components back to factory specs (ignition, carb, etc.) or added performance improvements (headers, free flow exhaust)....but....the biggest MPG improvement I've made in fuel consumption was just slowing down.

I would routinely run between 65 and 70 (basically just running the posted limit). But on our last two big trips (KY - FL and KY - ME) I tried an experiment and just slowed down to between 55 - 60. We saw a big difference in MPG. For example I ran from Scranton PA to Cincinatti OH on one tank of gas and that was while towing a car behind the AS.

Funny thing is, most of those cars and trucks blowing by me will blow by me three times as they need to stop for gas or a nature break or a soda or whatever. We just keep on truckin' and end up keeping up with their overall pace over 400 - 500 miles.
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Old 08-14-2005, 09:53 PM   #4
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I commute with my Duramax and I started traveling at 60mph in the slow lane and found that my mileage is a steady 19.3 mpg. One other benifit to this is I get 5 more minutes for morning coffee. It's great to see the world pass on by.

In towing, I find 60mph will give me about 15 to 16mpg. I tow a 7000lbs equipment trailer and it is the same with our Minuet, go figure.

I am going to try synthetic oil along with synthetic rear end and front end gear oil. I have read this will get you an additional 3 to 8% more miles per gallon. Hope it works.
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Old 08-14-2005, 10:07 PM   #5
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I pull at 58-62 mph. It is my compromise between reducing wind resistance and getting run over. My gmc is gasoline but, the factors are the same; wind resistance, horsepower, engine torque, gearing, rolling resistance, tire pressures, etc.

If you slow down, you need to increase your speed somewhat as you go into hills, because I believe you will be below the rpm where the diesel is getting its maximum torque. The GM literature usually has horsepower and torque graphed. You lose a lot if you have to come out of overdrive. I also think that cruise control doesn't help mpg pulling heavy and especially in hilly country like Missouri.

I also think you can cheat up a little on the downhills and run 62 or maybe more.

It's not rocket science, and you get feedback by the tankfull.
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Old 08-14-2005, 11:00 PM   #6
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Quote:
Originally Posted by Janet's Husband

I am going to try synthetic oil along with synthetic rear end and front end gear oil. I have read this will get you an additional 3 to 8% more miles per gallon. Hope it works.
I use synthetic across the board on the Impala (nearly all oil based fluids). At one time it too towed the Safari. Using synthetic had zero effect on MPG....if it does, I was not able to detect any MPG gains with it. My main motivation for going synthetic was that it takes a bit more of a beating than conventional oils, but MPG improvement from my tests just didn't happen.
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Old 08-15-2005, 12:50 AM   #7
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Quote:
I am going to try synthetic oil along with synthetic rear end and front end gear oil.
gary

GM beat ya to it, on the rear end anyway. they have been coming from the factory since '99 with synthetic 75W90.

you can go with synthetic in the front, since it windmills 99% of the time i doubt you will see much change. do not overfill, it will blow out of the breather leaving quite a mess under the hood. (don't ask how i know!)

one nice thing about the newer chevys is that you have a drain plug on the rear end, so changing oil is a snap!

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Old 08-15-2005, 05:55 AM   #8
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You folks with the Duramaxes are seeing just about what I see. Just changed my oil to Mobil 1 Truck and Suv, 5W40, this weekend, we will see what happens.

You can install a propane injection system on your diesel. That will give you 3-5 mpg, and more horsepower. Systems start at around $1000 for a Dmax. Not sure what the ROI is, have to run a spreadsheet and see. A lot hinges on what you can get the propane for. Really pays for the farmers that get it for $1 or so a gallon.
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Old 08-15-2005, 07:31 AM   #9
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Quote:
Originally Posted by Pick
You folks with the Duramaxes are seeing just about what I see. Just changed my oil to Mobil 1 Truck and Suv, 5W40, this weekend, we will see what happens.

You can install a propane injection system on your diesel. That will give you 3-5 mpg, and more horsepower. Systems start at around $1000 for a Dmax. Not sure what the ROI is, have to run a spreadsheet and see. A lot hinges on what you can get the propane for. Really pays for the farmers that get it for $1 or so a gallon.
One of my customers installed a propane conveersion on his Ford 7.3 PSD, among several other upgrades.
He now has a 700hp engine, with 1000 lb/ft of torque, and gets 21 mpg while carrying his truck-bed camper. And it only cost him $20,000, including the new transmission we had to upgrade/install to handle the higher figures.
The transmission was $3500 installed, the propane injection system was $2200 installed, he got a Banks turbo and exhaust, and other goodies I have forgotten.
The down side is, the truck sounds like an F-16 driving down the street.
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Old 08-15-2005, 08:15 AM   #10
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Quote:
Originally Posted by maxandgeorgia
Max ususally drove in the 70-75 mph range. Lately, I proposed limiting our speed in the truck to 60, max. What are other methods for improving gas mileage? .
put ol' leadfoot in the passenger seat and take over the driving duty... your mpg might improve a little, as it is just getting broken...
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Old 08-15-2005, 09:07 AM   #11
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My elderly dad installed a vacuum gauge on his intake manifold (as used on private aircraft) and used it to monitor power needed/used. Just very small changes to pressure on the gas pedal would result in very large savings (or loss). The result in his case was significant savings.

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Old 08-15-2005, 09:11 AM   #12
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I nearly doubled the fuel milage on my 2004 Duramax by leaving it parked and doing my daily driving in an '87 Mercedes 190 diesel. So far, no convenient way to improve the towing milage, however.

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Old 08-15-2005, 09:16 AM   #13
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i would like to see a comparison between identical pickup trucks with and without truck caps.

gotta think there would be a gain without added drag of wind swirling in the empty truck box.

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Old 08-15-2005, 09:25 AM   #14
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Quote:
Originally Posted by eubank
My elderly dad installed a vacuum gauge on his intake manifold (as used on private aircraft) and used it to monitor power needed/used. Just very small changes to pressure on the gas pedal would result in very large savings (or loss). The result in his case was significant savings.

Lynn
Many Airstream motorhomes have an in dash vacuum gauge labeled as the "Fuel Economy". Brett (thenewkid64) once labeled it the "Lack of Fuel Economy" Gauge which is far more appropriate.
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