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ChiefMechanicMark · 03-26-2017, 04:35 PM

I couldn't get the first video to play all the way through but I think I saw enough. So first thing I heard you say was your speedometer is not accurate so if possible drive by your GPS for speed limits. Second thing I would suggest is put your transmission in manual and shift it between the 1200-1500 RPM If the gears are close enough to together the engine will pull the load just fine. Even if it dips to 1100 RPM or so, it should still be able to pull it. The more often you go up in RPM the lower your fuel economy will be. It does not hurt to "Lug" these engines into their torque range and keep it there. The high end if you have to go would be no more than 1600 -1700 max RPM to bring it back in after an upshift to the 1100-1200 RPM range.
Granted this is going to make you slower off the line but you will be surprised that even shifting this way it will still get up to road speed fairly quickly and you will gain fuel economy.
I know I always add stories but that is how I am...
I had a driver of a 400 HP Series 60 with a 10 speed manual transmission in an over the road truck who came into our Seattle facility complaining of low power and poor fuel economy. His average fuel economy was between 4 & 5 MPG He had a fully loaded 53 foot trailer so we were loaded at 80,000 pounds.
I plugged in my hand held computer (Prolink) and took him on our test drive route which included a long drawn out hill of about 2 miles at a 5% grade off of a draw bridge to a slight downhill about 1/4 mile long. We hit the bottom of the bridge grade doing about 45 mph at 2100 RPM in I think 7th gear. I watched him drive and said nothing as he shifted 2100-1600 keeping his foot flat on the floor the whole way but kept hitting 2100 everytime before would shift. As soon as the RPM dropped to 1600 he would downshift to a lower gear and the RPM would go back to 2100. We were doing 35 MPH at 2100 RPM in 6th gear at the top of the hill.
I had him turn around at the off ramp and drive back down to the bottom of the hill. There was a turn around so we did not have to go on the draw bridge but we had to start from a dead stop to go back up the hill. This time I told him he had to shift when I told him no arguments. I told him to run his throttle just the same but he had to shift when I said so. We took off in low gear and he shifted everytime I said which was at 1500 RPM. Half way up the hill we were in 10th gear and doing 60 MPH at 1200 RPM. He said he never would have believed it if I had not made him do it. The "Prolink" had a fuel consumption reading in it and we were using about 2 GPH (Gallons Per Hour) less fuel driving my way than his.
The Autoshift transmissions are great don't get me wrong... But they're still susceptible to having to anticipate what it can't see which is approaching grades and traffic. In manual transmissions I always use Low gear to get rolling so I have no chance to slip a clutch and then I never touch the clutch pedal, just using the RPM to shift (Floating) the gears. The Automatics are doing the same thing except they don't use the Low gear and in your case with out having 80,000 pounds or more it probably won't slip the clutch by taking off in 3rd gear.
I truly believe the more you can keep those RPM down the better fuel economy you will see.
Also be sure and test your speedometer and odometer accuracy aganst a stop watch and measured mile markers. If it's wrong your fuel mileage calculations will be wrong too.
Until you change rear axle ratios though you will never get Bushpilots fuel mileage.
Hope this helps...

03-26-2017, 04:35 PM	#29
ChiefMechanicMark Member Join Date: Mar 2017 Location: Redmond Posts: 54	I couldn't get the first video to play all the way through but I think I saw enough. So first thing I heard you say was your speedometer is not accurate so if possible drive by your GPS for speed limits. Second thing I would suggest is put your transmission in manual and shift it between the 1200-1500 RPM If the gears are close enough to together the engine will pull the load just fine. Even if it dips to 1100 RPM or so, it should still be able to pull it. The more often you go up in RPM the lower your fuel economy will be. It does not hurt to "Lug" these engines into their torque range and keep it there. The high end if you have to go would be no more than 1600 -1700 max RPM to bring it back in after an upshift to the 1100-1200 RPM range. Granted this is going to make you slower off the line but you will be surprised that even shifting this way it will still get up to road speed fairly quickly and you will gain fuel economy. I know I always add stories but that is how I am... I had a driver of a 400 HP Series 60 with a 10 speed manual transmission in an over the road truck who came into our Seattle facility complaining of low power and poor fuel economy. His average fuel economy was between 4 & 5 MPG He had a fully loaded 53 foot trailer so we were loaded at 80,000 pounds. I plugged in my hand held computer (Prolink) and took him on our test drive route which included a long drawn out hill of about 2 miles at a 5% grade off of a draw bridge to a slight downhill about 1/4 mile long. We hit the bottom of the bridge grade doing about 45 mph at 2100 RPM in I think 7th gear. I watched him drive and said nothing as he shifted 2100-1600 keeping his foot flat on the floor the whole way but kept hitting 2100 everytime before would shift. As soon as the RPM dropped to 1600 he would downshift to a lower gear and the RPM would go back to 2100. We were doing 35 MPH at 2100 RPM in 6th gear at the top of the hill. I had him turn around at the off ramp and drive back down to the bottom of the hill. There was a turn around so we did not have to go on the draw bridge but we had to start from a dead stop to go back up the hill. This time I told him he had to shift when I told him no arguments. I told him to run his throttle just the same but he had to shift when I said so. We took off in low gear and he shifted everytime I said which was at 1500 RPM. Half way up the hill we were in 10th gear and doing 60 MPH at 1200 RPM. He said he never would have believed it if I had not made him do it. The "Prolink" had a fuel consumption reading in it and we were using about 2 GPH (Gallons Per Hour) less fuel driving my way than his. The Autoshift transmissions are great don't get me wrong... But they're still susceptible to having to anticipate what it can't see which is approaching grades and traffic. In manual transmissions I always use Low gear to get rolling so I have no chance to slip a clutch and then I never touch the clutch pedal, just using the RPM to shift (Floating) the gears. The Automatics are doing the same thing except they don't use the Low gear and in your case with out having 80,000 pounds or more it probably won't slip the clutch by taking off in 3rd gear. I truly believe the more you can keep those RPM down the better fuel economy you will see. Also be sure and test your speedometer and odometer accuracy aganst a stop watch and measured mile markers. If it's wrong your fuel mileage calculations will be wrong too. Until you change rear axle ratios though you will never get Bushpilots fuel mileage. Hope this helps...