Fuel economy ideas and MPG Boosting (merged threads)

[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.

[overlander63]

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.

[swebster]

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.

[Janets Husband]

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.

[wingfoot321]

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.

[Silvertwinkie]

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.

[john hd]

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!

john

[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.

[overlander63]

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.

[norbert]

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...
norby

[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

[j54mark]

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.

Mark

[john hd]

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.

john

[swebster]

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.

[Chuck]

actually, there have been studies done, and it turns out that it makes little or no difference.

the "swirl" that typically occurs in an empty pickup bed actually forms a bubble, and the air coming up over the cab (where most of the drag occurs" slips over the top of this bubble.

when you open up the tailgate, it disturbs or eliminates this bubble of air, and actually causes more drag than if you leave the tailgate closed.

from my own experience, with my last truck, I had a tonneau for a while, and a cap for a while...drove around with the tailgate open a few times (meaning: I filled the tank, recorded the mileage, opened the tailgate and left it open until it was time to re-fill the tank...then actually DID the math). nothing made any difference. That truck got 15mpg, rain or shine. I usually kept track of it, and when the mileage went down, it was because maintenance was needed. the ONLY time I ever saw a significant gain was one extended vacation that I took, which involved driving a few hundred miles on secondary roads, where the speeds were fairly steady and 45-55mph. The mileage jumped up to 19 for that tankfull. I was shocked, and never saw that kind of mileage again.

[darryl97420]

The shop down the street continually has diesel powered pickups in there being upgraded for more horsepower and at the smae time gains 2-3 mpg.

After talking with Tim (manager of Tom & Gigs) here in Coos Bay. Here is what he told me. Keeping the diesel engine breathing effieiecntly is very important. Before they do any engine modifications they change the air intake system to something that will increase airflow into the engine and change the exhaust system to to decrease the exhaust temps.

After that there are other tricks to better gain HP and fuel economy but I didn't get it all written down.

Their shop rig is an 04 Dodge Cummings diesel that has been upgraded and it sounds very quiet (except when you push it) has around 70hp over stock and runs around 23 mpg while crusing the highway.

I guess there are not alot of places that do this kind of work so people from all over travel to Coos Bay to have this done so they are very busy.

Hope you don't mind me asking the pros down the street about ways other than tire pressure and general maintenance of the vehicle.

Darryl

[JeepinAudiophile]

Do you have the LB7 or LLY Duramax motor? I ahve heard good things about the tuning programs from www.westerscustomtuning.com. Especially good gains in mpg with the 8.1 motors. Check them out and give them a call, they'll be able to work out with you on specifics of a tune to give you max mpg, and then will figure out your price.

[overlander63]

Originally Posted by chuck

actually, there have been studies done, and it turns out that it makes little or no difference.

the "swirl" that typically occurs in an empty pickup bed actually forms a bubble, and the air coming up over the cab (where most of the drag occurs" slips over the top of this bubble.

when you open up the tailgate, it disturbs or eliminates this bubble of air, and actually causes more drag than if you leave the tailgate closed.

I did similar testing (got out pen and paper, and did the math) like you did. My mileage went up .2 mpg with a tonneu, and tailgate closed (of course). It held nearly steady with a topper (my theory is the extra weight of the topper negated the fuel savings of aerodynamics), maybe .1 mpg gain, if that, and lost .1 mpg with the tailgate removed, and no topper or tonneu cover. The plus of the cover or topper is you can haul stuff without it blowing away, or getting wet, and less chance of it being stolen, with a (very) small increase in MPG. However, we are talking MPG, not security this time around.
Keeping your vehicle properly maintained and tuned, and adjusting driving habits, seem to render the best results.

[overlander63]

Originally Posted by darryl97420

Hope you don't mind me asking the pros down the street about ways other than tire pressure and general maintenance of the vehicle.

Darryl

By all means, ask away, just don't keep the info a secret, we all would like to know.
There are things you can do, like reprogramming the ECM, to improve horsepower and milage, but that can create a problem with warranties, and possibly emmissions tests, so I didn't want to bring it up, as advice to do.
The F350 owner I mentioned above is real handy with cash, so was able to buy nearly every accessory that can add extra power. We don't have emmissions testing here (yet) so he can get away with his mods for now.

[wahoonc]

Originally Posted by overlander63

I did similar testing (got out pen and paper, and did the math) like you did. My mileage went up .2 mpg with a tonneu, and tailgate closed (of course). It held nearly steady with a topper (my theory is the extra weight of the topper negated the fuel savings of aerodynamics), maybe .1 mpg gain, if that, and lost .1 mpg with the tailgate removed, and no topper or tonneu cover. The plus of the cover or topper is you can haul stuff without it blowing away, or getting wet, and less chance of it being stolen, with a (very) small increase in MPG. However, we are talking MPG, not security this time around.
Keeping your vehicle properly maintained and tuned, and adjusting driving habits, seem to render the best results.

Consumer Reports did this a few years back...far enough back that I can't find it in the bathroom stack
and came to the same basic conclusions. We currently use a soft tonneau cover on ours...I would prefer the cab height shell...but the truck belongs to my wife

Aaron