I did some more measuring and testing for the MPG crowd. Before I start I will say that I just verified my SGII and its right close to being on the money (off by 0.2 gallons). I'll assume that a slight error between the ScanGauge and the fuel pump.

Now I my truck conditions are Edge set for 5x3, IAT fooled to 143*F, Engine coolant varied from 188*F to 197*F, winter fronts still on. Actual weather was high of 65*F (actual IAT was ~90-105*F)

Now since I was on I-84 down in southern Idaho today I figure I open the beast up and let it fly low for once. So I set the cruise for 75 MPH and reset the current MPG counter and measure for about 20 miles of highway. I was pulling roughly ~13 MPG. Then after shopping in Nampa, ID and got back on the same stretch of highway again and set my cruise this time for 65 MPH then reset the ScanGauge II again and measured about 20 miles of highway again. I turned out ~18 MPG.

Then even with all the playing driving fast and slower I still pulled in the yard with a total of 22 MPG.

So from this rough measurement I found that roughly for every 10 MPH above 55 MPH I lose roughly 5 MPG.

This is calculated numbers here. According to Google Maps its 300 miles round trip what I drove.

Time to travel distance

300 miles / 55 MPH = 5.4 Hours

300 miles / 65 MPH = 4.6 Hours (0.8 hours less than 55 MPH)

300 miles / 75 MPH = 4.0 Hours (0.6 hours less than 65 MPH, 1.4 Hours less than 55 MPH)

Amount of fuel consumed

300 miles / 21 MPG = 14.2 Gallons (@ 55 MPH - not a true 55 MPH because of testing)

300 miles / 18 MPG = 16.6 Gallons (@ 65 MPH)

300 miles / 13 MPG = 23.0 Gallons (@ 75 MPH)

Cost difference @ $4.019 Gallon (which I paied for)

14.2 Gallons x $4.019 = $57.06

16.6 Gallons x $4.019 = $66.71 ($9.65 more than 55 MPH)

23.0 Gallons x $4.019 = $92.43 ($25.72 more that 65 MPH, $35.41 more than 55 MPH)

Another tidbit. I get the same MPG's towing my RV at 55 MPH than I do driving empty at 75 MPH. Also the fuel consumption rate at 75 MPH is just about the same as climibng a 5% to 6% grade at 55 MPH. This shows that amount of rolling resistance and wind drag differences between 55 and 75 MPH.

This is great info, thanks Mike. But I have a problem with all those other cars just passing me all the time when the speed limit is 75mph, I just can't take it (lol). I'm coming thru again next month I'm going to try to stay around 70 -75 mph, I know I can get 17-18 mpg. Sometimes I wish I had 3.55 gears. The cost of gears buys a lot of fuel. Then I'd have to buy smaller tires, then I think it would look funny. Not doing it. Thanks again.

This is great info, thanks Mike. But I have a problem with all those other cars just passing me all the time when the speed limit is 75mph, I just can't take it (lol). I'm coming thru again next month I'm going to try to stay around 70 -75 mph, I know I can get 17-18 mpg. Sometimes I wish I had 3.55 gears. The cost of gears buys a lot of fuel. Then I'd have to buy smaller tires, then I think it would look funny. Not doing it. Thanks again.

I loved being passed by other vehicles. Because the rare chance I catch one in a fuel station and talk to them typically they are blown away by the MPG numbers I put down with a 7,500# vehicle vs. there little rice rocket. Then after as they make several stops, food, bathroom or for fuel and the owner trying to figure why he's got to pass my slow truck again. Which I didn't need to stop for fuel since I'm not wasting driving fast. I'm still ahead of them... Back to the hare and the turtle race again. Tires and gear are the ultimate way of getting the most MPG's. But some are just hard set on the big heavy tires and 4.10 gears. Your truck and your money... What can I say?

13 MPG ouch. I went and fiqured out my fuel consumption for the last year. There was no changes to the truck through out the year. It stays in the garage during the winter until the roads clear off. So outside temp was above 30 degrees for all of it. I started driving it on 3-19-12 and parked on 11-21-12. I fill at the same gas station, if I fill anywhere else I make a note of it. I did fill the truck once at Fleet Farm last year and that was it, everything else came from the same pump at the same gas station. So I feel my gallons added is accurate. Total gallons used - 314.715Total cost - $1242.33Miles driven - 5,362Avg MPG - 17.037My best was in April I went down to Chicago with my uncle to look at an '06 Dodge diesel(he bought it). It was a mix of 60 and 70 MPH with 45 minutes spent sitting in traffic idling due to construction. I averaged 22.62 MPG with a head wind on the way down and tail wind on the way back. I was not driving for milage, I was driving how I normally drive.My worst was in July. Went camping with the 32ft gooseneck enclosed trailer in tow. It weighs around 9k loaded on average. I filled up at the station with the trailer and drove to the campground. Didn't drive anywhere with the truck. Then drove home and filled up at the same station with the trailer still in tow. Well over half of the miles were interstate driving at 70 MPH. Head wind on the way there and tail wind on the way back. I averaged 14.48 MPG. I towed alot last year it was probably 50/50 overall. The gooseneck enclosed trailer probably accounts for 2/3rds of the tow miles with a boat taking care of the remainer. This year should be interesting with the Spyntec's. Itching to get it out if it ever warms up and the roads clear. Also I keep all this in a notebook in the truck. Just thought I would post for comparsion.

I loved being passed by other vehicles. Because the rare chance I catch one in a fuel station and talk to them typically they are blown away by the MPG numbers I put down with a 7,500# vehicle vs. there little rice rocket. Then after as they make several stops, food, bathroom or for fuel and the owner trying to figure why he's got to pass my slow truck again. Which I didn't need to stop for fuel since I'm not wasting driving fast. I'm still ahead of them... Back to the hare and the turtle race again.

I might have to entertain that idea, on the next trip. I do find I get best mpg at 1900-2000 rpm. It's worth a try if I can take it. My father used to tell me he could get 20 mpg out of this thing, haven't seen it yet, but he was older and mature...

I wonder what the grade was if any Mike was running on when you did the tests?

Idaho is one long rolling up and down grades. Even the full trip from home to Boise is all downhill. Then its all up hill going home. This is in a manner of speaking looking at elevation changes over the full length of the trip which my GPS can measure for. I can get a profile of the elevation changes as a cross section. I was messing with a bit of math like ISX love to do. Here is a spread sheet of numbers. Some of it speculation and some of its actual measurement. Now 45, 50, 70 and 75 MPH are speculated MPG numbers. Everything else is a result of math and calculation. The 2 drag figures below are truck alone and the truck and RV. So even with my truck I got to over come 67.4 HP worth of wind drag at 75 MPH... I know my truck stands nearly 7 foot tall compared to 2WD truck which are nearly a foot shorter. the sq/ft of frontal area make a huge change on wind drag figures. So at 55 MPH I only losing 26 HP to wind drag. Formula is from here.. http://gtechprosupport.com/support/AeroDragCalc.htm

As I said I give up... Closed.