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Old 04-15-2008, 08:48 AM   #1
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Because I知 not in a hurry

this is sorta long so you may wanna sit down


I drive a big truck. See my sig. Everyday driving doing the speed limit back and forth to work 25 miles 18 highway at 65mph the other 7 stop and go I get an average of 16.4 mpg. The last few of weeks of driving (when I知 not riding my scooter due to weather sick) I decided to slow down 5mph to 60. This slowed my commute time by about 3 minutes depending on how I hit the traffic lights and I can live with that. At half a tank I filled up (it doesn稚 hurt as bad compared to a full tank) and figured my mileage and it went up to 17.6mpg. Hmmmmm not bad, that痴 over 1mpg and on a 38 gallon tank that would save me just a scosh over 2 gallons (2.16) which equates to $8 of hard earned cash as diesel is right at $4 a gallon. In fact it痴 the BEST I致e ever gotten. Even straight highway the best has been 17mpg and I think I had a tail wind that day and it was all downhill and I was probably drafting a semi. Well this past weekend we needed to make a trip that was 270 miles down the highway. The speed limit on most of the interstate is 70mph and here lately I would just do 65 anyway because of mileage. At 70mph I would get just over 15mgp.In a perfect world 270 miles at 70mph = 3 hours 51 minutes. 270 miles at 65mph = 4 hours 10 minutes. 270 miles at 60mph = 4 hours 30 minutes. Ok we know it痴 not a perfect world and there is ALWAYS traffic involved that causes you to slow down or even stop in some cases (I致e never made it faster than 4 hours 10 minutes even driving 75mph). The difference in time between 70mph and 60mph is 40 minutes but like I stated I致e NEVER made it faster than 4 hours 10 minutes (well except that one time doing 80+ but we won稚 go there). So I知 really dealing with a time difference of only 20 minutes. I decided to do an experiment to see what kind of fuel economy I get in my truck unloaded for a nice long distance and see if that slower speed adversely affects my drive time and my temper. Here are the results of my trip:

I had 58 miles already on the truck as I had driven to work on day previous to the trip and it also had a fuel trip (the extra 8 miles) on it. These 58 miles were all done at 60mph with the bit of slower speeds in the stop and go areas. We made the trip down in the evening and set the cruse control at 60mph. Traffic was light and we only had to stop cruse twice for traffic. Total time for the trip was 4 hours 35 minutes and I can live with that as it was only 25 minutes longer than my best normal time. After arriving at our destination we put an additional 42 miles on the truck running errands around town (more stop and go and some highway). When we stopped to fill up we had 370miles on the tank and the gauge was at 5/8ths of a tank (normally if I have 340miles at ス tank It痴 a 16mpg run). I filled up and put 18.3 gallons of gogo juice in the tank. When I fill up I TOP it off. After the auto shut off I can still squeeze in 4 gallons of diesel (yeah I知 the butt-head taking his sweet time while you wait ) because I like to get as far as I can on a tank and it also makes for more accurate assessment of fuel economy. I do the math and my fuel economy was 20.2mpg. Ok, I do the math again because I must have messed up somewhere. Nope, I didn稚 mess up and the numbers don稚 lie. That痴 an extra 3.8mpg over normal! On a 38 gallon tank that痴 an extra 144 miles that I can drive. Ok I know I will probably NEVER get that mileage again. Or will I? The trip back we did the same thing. 60mph. Traffic was considerably heavier and cruse went off well over 20 times. We also started having a 20+mph head wind about halfway through the trip due to a front moving in. When we stopped at the house we had 274 miles on the tank and were just under セ tank full. Trip time was 4 hours 45 minutes and that痴 still ok and to be expected with the traffic we hit. The truck hasn稚 moved yet as I致e been riding my scooter to work. The next time I have to drive the truck I will top off on the way home to see what the mileage was. I know I won稚 have the 20mpg again but it will be well over the 16.4 I知 sure. When I do fill up I will post the numbers.

Needless to say I am amazed at the difference that 5mph makes in fuel economy. I usually tow at 60-65mph and get anywhere from 11-12.5mpg. My next trip I知 going to slow down a bit and try 55-60mph and see what happens. Maybe I値l break the 13mpg barrier?

Just thought I'd share.

greg
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Old 04-15-2008, 09:11 AM   #2
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Excellent post! Real world experience is worth tons. I usually drive 60 mph going to work and 65 going home (I'm not in a hurry to get there but am to leave, I guess ) and I average about 20mpg. We're going camping a good distance in two weeks and (unlike our normal camping trip) we won't be in any hurry to get there so I'll try and keep it 55 and below and post the results here. Maybe if a few of us try it we can get realistic expectations.
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Old 04-15-2008, 10:07 AM   #3
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If I drive 68 MPH with the cruise ON I get 9.5/10 mpg.
If I drive 60/62 MPH with my foot I can maybe squeeze out 11 mpg.
I figure I'll fill up at around 1/4 tank which is about 20 gallons.
1 extra mpg when we're talking 10 to 11 mpgs means I save about
a gallon out of every 10 or 2 gallons out of a 20 gallon fill up.

Gas spiked yesterday at $3.58 so if I save 2 gallons per fill up I can
get a free $7 lunch with every fill up.
It's a lot easier to drive with cruise on because I don't have to constantly
watch the speedo. Sometimes I use my foot, sometimes I use cruise.

I imagine I'd gain another 1 mpg at 55 MPH but EVERYTHING blows by
you at 55. It's not the big rigs so much as the $%^@* SUVs and
mini vans that jump back in my lane when they're still practically even
with my front bumper ;-(
There is a certain safety factor involved when you are more or less
keeping up with traffic.
At 5 under the predominate speed, it's not bad at all.
At 10 under it's starts to get hairy and at 15 under it can be downright
scary at times.

My 2「
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Old 04-15-2008, 10:10 AM   #4
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Ok I see you run a tuner and changed the intake. My question is have you changed the exhaust in any way. We are changing ours this weekend to try to up our mpg. The intake will be here as soon as it is off back order. and we are still shopping for the tuner. any more suggestions?
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Old 04-15-2008, 10:20 AM   #5
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Ok I see you run a tuner and changed the intake. My question is have you changed the exhaust in any way. We are changing ours this weekend to try to up our mpg. The intake will be here as soon as it is off back order. and we are still shopping for the tuner. any more suggestions?
Yeah I'm running a tuner. I have it on the mid setting while running empty and use the low setting while towing. I have not modified the exhaust except to add an EGT gauge. I also have gauges to monitor turbo boost and transmission temps. I've tried all 3 programs while running empty and the mid-level program produces the best mileage. Towing I have run the low and mid-level programs and the low program produces the best mileage and the lowest EGTs. In fact, running the tuner produces lower EGTs than running stock. Go figure. Everything I've been told and read would have suggested otherwise.

Another thing I do is run higher pressure in my tires than what's on the door sticker. The sticker says 62psi all the way around. My tires are load range E and rated at 80psi cold. I run 75psi while towing and 70psi empty. Don't know how much of a difference in mileage it makes empty or towing but I do feel better with more air while towing. I haven't noticed ANY difference in ride with the higher pressure in the tires.
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Old 04-15-2008, 10:28 AM   #6
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Originally Posted by KyDan View Post
There is a certain safety factor involved when you are more or less keeping up with traffic.
At 5 under the predominate speed, it's not bad at all.
At 10 under it's starts to get hairy and at 15 under it can be downright
scary at times.

My 2「
Understood and it also depends on where you are at. If I'm on loop 635 in Dallas I don't do anything less than 65 and I flat out don't drive it on my scooter. Running up and down the main interstates though is no major running 15 under the posted limit. As far as the SUVs and soccer moms go......... My dually is bigger. They clip me and they are spinning out.

Riding my scooter....... speed is my friend
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Old 04-15-2008, 03:46 PM   #7
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greg
in my 2002 7.3 if i ran the tuner n the 80 hp load i got 16 highway at 75
versus 13 in the stock mode
that was with a 4' exhaust and free flow muffler
4.10 rear gears






now in the edge if we cruies at 80 we get 24 mpg and at 70 it gets 22 ????

in town a solid 21.???
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Old 04-15-2008, 03:54 PM   #8
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greg
in my 2002 7.3 if i ran the tuner n the 80 hp load i got 16 highway at 75
versus 13 in the stock mode
that was with a 4' exhaust and free flow muffler
4.10 rear gears
my tuner has 40hp, 60hp, and 90hp? programs
on the high program the mileage drops like a rock
It does better stock

my exhaust is stock as well, I'm bettin a 4" would help but I'm not forking out the cash for one
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Old 04-15-2008, 11:15 PM   #9
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The older I get...the slower and safer I seem to drive.
I guess I'm never in that big a hurry. I'm a never late...always early kind of person.

By the way, I heard some truckers talking. They were talking about how they've slowed down to save on fuel costs. Some companies they drive for have ORDERED them to slow down to a certain speed. Of course...there are stil 'the crazies' out there....

I guess it's time to think harder about MPG.
Easiest way I know to save:
~drive something that's better on gas...or walk, bike, or (insert other here).
~slow down.
~keep correct tire pressures
~keep that air filter clean.
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Old 04-18-2008, 07:56 PM   #10
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Ok I topped off yesterday and finally got around to the math and it worked out to 18.4mpg. Still not to dang shabby as it's right about 2 over what I normally get running empty.

So my conclusion is it is definitely worth it to me to drive a bit slower in most cases. There are situations were 5, 10, or even 15 under are NOT safe or sensible but for the most part in my dually it just don't matter. The wife's saturn and my scooter are a different story. 5 under max for the car and the scooter are usually at the limit or 5 over.

Now for the disclaimer.
Neither FRF nor anyone associated with this web site take any responsibility for your actions. YOU DO. Neither I nor FRF advocate that anyone drive below the posted speed limits or slow enough that the flow of traffic is impeded to an unsafe level. If you attempt to do something similar on your own you are ON YOUR OWN.


Be safe out there. Nothing can replace common sense. And if you don't have any, ask around you might find some.
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