Fg fuel economy

[kerry]

Any thoughts on the following numbers:
I bought my FG in NC and drove it home to CO with just the service body and tanks. I was running the AC for virtually the whole trip. Got 13.74 mpg on average over the 1466 miles traveled.
I drove it from Denver to Alamosa with the camper fully loaded this past weekend. Got 11.07 mpg going there. Had the AC on the whole time. On the trip home it was obvious from the fuel gauge that I was getting better fuel economy. It got 14.34mpg. I was not using the AC.
It appears that the AC is consuming a fair amount of fuel. Is this typical? I'd expect perhaps a 1mpg difference, but more than 3mpg? I don't think there is a substantial difference in amount of climbing involved going to or from Alamosa to Denver.

 

[redbeard]

Wind might add something to this too..I think it generally blows west to east over most of the country. Was it windy?

 

[kerry]

I didn't notice any substantial difference in the winds.

 

[whatcharterboat]

Hi Kerry,

Temperature? Was it colder on the way back? Colder air gives a little more power. More noticeable on a turbo engine than a NA one. I presume it was colder if you weren't running the A/C. Just a thought. Although I wouldn't have thought it would make that much difference.

 

[kerry]

Probably about 8 degrees Fahrenheit cooler on the return trip.
Is it possible for there to be a problem in the AC system causing it to consume more power?

 

[Jacob7963]

On my cross country trip I averaged around 11.5-14.5 mpg. Looking back I think some of the higher numbers were at higher elevation (less wind resistance) and colder temperatures. In Florida with the A/C was on the lower end of the range.

That is all a little backwards to me compared with my Honda Insight. It gets about 20% better MPG in the summer. But it has a gas engine, and a lean burn mode that only activates at higher temperatures.

 

[Tom_D]

Mpg

Your figures are consistent with mine over the 20,000 miles I have driven the FG through Alaska, Canada and the northern US. I find speed the determining factor. 60+mph means 11 mpg. slow down to 50 mph (35mph on the Dempster hwy) and I average 13+mpg. I usually average a little under 12 overall since highways account for most of the actual mileage and I am always running at 13,000 - 13,700 lbs GVW.

I do usually run the AC. I will have to pay more attention to its effect on the mileage. I will be carrying two sea kayaks on the roof this summer so I may see an all time low mpg...

Tom

 

[kerry]

I will be carrying two sea kayaks on the roof this summer so I may see an all time low mpg...

Tom

So it looks like my numbers are not out of line. I was carrying 2 canoes on the roof.

 

[lehel1]

mpg and air ??

hello all

on my o8 fg i definitly have noticed a power and mpg change with the ac on. climbing the siskiyou mountain which i do every week with a load of feed for the store, i can climb the 6% grade in fourth at 45 mph. with the ac on i can not maintain 45 and it ever so slowly slows, turn the air off and i just make it once again. i'm right on the edge of being able to hold this speed making it alittle easier to see the difference.

for me so far, 14-15 mpg if i keep it under 60, 12-14 if over 60, 12-13 with a load regardless of speed. i have not experienced under 12 yet. i'm loving the second gas tank we added and hit 800 miles the other day before refueling. great for the remote area we live in.

our new 19.5 wheels delivery from stockton wheel is running late, be interesting to see how this will affect mpg and power band. we're hoping to have them installed this week sometime.

cheers lehel and laura

 

[kerry]

Yes, I'm curious about the larger tires and power band. Living in Colorado, I do a lot of climbing and I've been able to do all the major grades in 4th gear. I am thinking that larger tires may cause that to decrease to third. I've been amazed at how steep a grade the FG can pull with the camper on it in 4th gear. I even climbed all the up the western grade of La Veta pass in 5th gear.

 

[dhackney]

Kerry,

We averaged 9.97 mpg / 23.63 liters per 100 km for about our first 20k miles.

Most of that was in the Rockies and the Andes.

Best was 15.99 mpg / 43.01 lp100km.

Worst was 5.47 mpg / 14.71 lp100km.

I think it's fair to say we were probably heavier than your Fuso.

I don't have the mileage log for the section 20k - 30k miles calculated, but I didn't notice any big differences during that segment.

I also didn't notice any big differences with A/C and non-AC, but we were running, generally, 50 to 75 gallons between refills (100 gallon tank).

Because we spent most of the 2 years at altitude, we didn't use the A/C all the time. The exception was in Utah and Idaho, where it was very hot out.

The biggest variable with A/C for us in the mountains is engine temp. When climbing we run the cab heater as an auxiliary heat sink.

Due to our weight, in the Andes we were in 2nd on some chicken bus road climbs, and even 1st on a few memorable occasions, but those were more tracks than roads. Only had to dump it into low range once to make a climb, if I remember correctly.

On grades typical in the U.S., including up and back from AZ to ID to AZ through the Rockies, 3rd and 4th were common, 2nd rarely. Again, we were a lot heavier than you are. YMMV.

I did run in low range 4x4 for mountain work quite a bit, but that was more as a convenience in having a better fit between typical ground speed and the gearbox. There is such a huge chasm between 3rd and 4th, it helps to move that to a different place relative to RPM and speed when you are working on what would probably not be considered roads to most people in NA.

Doug

 

[charlieaarons]

larger tyres and a modified exhaust should help fuel economy.

Larger usually don't help fuel economy for the following reasons: increased ground clearance allows more air to go under the vehicle, which increases air resistance; more rolling resistance; and the effect on gearing can often push the vehicle into a worse zone on the 3 dimensional rpm-load-BSFC graph, and can require downshifting on shallower grades, especially when heavily loaded with a high air resistance camper.
For reference, my U500, which weighs 25500-27500 lb, gets 8-9 mpg on the highway at 60 mph. On the Alaska Haul Road (Dalton Highway), it only gets ~7.0, due to steep grades requiring downshift from 8th to 6th or even 5th and heavy use of exhaust brake on steep downgrades which wastes gravitational potential energy stored in upgrades. In France once, while new, weighing less, following a MAN 6X6 who insisted on ~53-54 mph, using 5W-30 oil, I got almost 10 mpg.
My tanks hold 162 usable gallons.

Charlie

 

[ozzyfishaman]

Yes, I'm curious about the larger tires and power band. Living in Colorado, I do a lot of climbing and I've been able to do all the major grades in 4th gear. I am thinking that larger tires may cause that to decrease to third. I've been amazed at how steep a grade the FG can pull with the camper on it in 4th gear. I even climbed all the up the western grade of La Veta pass in 5th gear.

Hi Guy's how did you find the difference with the bigger tires ? and what size tires did you fit. John