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Old 10-08-2016, 05:41 PM   #21
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Well said !!
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Old 10-08-2016, 07:21 PM   #22
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Originally Posted by mustang94@hot.rr.com View Post
LOL.... Hmmm.... looks like I left out Colorado and the return trip...
There you go. That could explain the 9.8 MPG at 75 MPH.


Seriously though, did you check each tank separately, or the total trip as one? With an overall average of 9.8 MPG some tanks must have been well above 10 MPG. I'd be curious to know which part of the country gave you best fuel economy.
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Old 10-08-2016, 07:47 PM   #23
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I made a cold air intake with dryer vent hose and dryer vent which is zip tied to back of grill. Intake on air box is 4" and vent hose clamps on perfect. Cooler air equals better mpg and slightly better performance, now intake is not drawing from hot engine compartment. Easy to do for less than $10 and about 15 min.
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Old 10-08-2016, 09:19 PM   #24
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If you're getting 9+ mpg on the Ford V10 motorhome you must be living right, I had a couple F350 4x4 pickups at work that never ever saw 9 mpg & hook a trailer behind it & it barely made 6 mpg, but it would pass everything but a gas station as it only had a 25-26 gallon tank.
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Old 10-11-2016, 03:24 AM   #25
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OK we just got back from our first big trip 2779 miles round trip from Fort Hood Texas to, New Mexico, Colorado, Ogden Utah, then over thru Wyoming, Oklahoma back down Texas to Ft Hood. We were not towing anything and only ran the generator a few times for about 2 hours total. We averaged 9.8 miles per gallon. Tried driving 75MPH when ever possible. I really think this is good considering our over all size and weight.
WOW.... so sorry put I recalculated everything and I was WRONG. It wasn't 9.8 but was 7.99 MPG. Here are my numbers for that trip....

479 miles 65 gallons 7.36MPG
334 miles 40 gallons 8.35MPG
396 miles 39 gallons 10.15MPG almost all down hill
217 miles 37 gallons 5.86MPG very hot and ran generator
257 miles 37 Gallons 9.64 MPG return trip and mostly down hill
165 miles 21 gallons 7.85 MPG
345 miles 43 gallons 8.04 MPG
481 miles 65 gallons 7.4 MPG last leg home and was pushing it
total miles gas avg. MPG for the trip
2775 miles 347 gallons 7.99

Still not bad numbers....
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Old 10-11-2016, 01:57 PM   #26
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Okay Dan, those numbers don't make me feel so bad! We just completed a 1350 miles run towing. Granted my tow is only a trike on an aluminum single axle trailer (1600 pounds total), but my trip total mpg was 7.37. That was Illinois, Kentucky, Tennessee, Alabama, Florida, with just a few hills and no serious grades. Kept speeds between 64 and 68mph and did not run gen set.

Based on your numbers and mine I would say we get about the same MPG.
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Old 10-11-2016, 03:56 PM   #27
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8 MPG is still good for large motorhomes built on 22,000-pound chassis.

Weight isn't as important as many owners think, otherwise motorhomes roughly half the weight would be getting twice the mileage (close to 16 MPG) and that clearly isn't the case. Weight is somewhat important but plays a lesser role in MPGs.

Aerodynamic drag remains the #1 biggest enemy to fuel economy on the highway, which is why slowing down helps so much. It also confirms why much lighter Class As built on 16,000-pound chassis but with similar frontal area get approximately the same MPG on the highway.

I'm personally hopeful that with some design effort and attention to aero design, that smaller Class As can soon get 12 MPG or thereabouts. If these big MHs can get 8 MPG, then 12 should be very doable for smaller units.
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Old 10-11-2016, 04:27 PM   #28
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Just returned from our latest (and last for the year) trip. Blasting 75 mph (or more) down the highway with the generator going for 200 miles yields a paltry 8.5 mpg from our Axis.
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Old 10-11-2016, 07:26 PM   #29
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Just returned from our latest (and last for the year) trip. Blasting 75 mph (or more) down the highway with the generator going for 200 miles yields a paltry 8.5 mpg from our Axis.
That's also pretty good considering your speed.

Just for the fun of it, I did a little reverse engineering to see what the difference in speed would do if you slowed to 60 MPH (80% of 75 MPH), making some reasonable educated assumptions, and it turns out that slowing from a steady 75 to 60 MPH could bump your fuel economy to around 12 MPG -- provided engine efficiency remained the same. Unfortunately it won't because the V10 is too large to be efficient in an Axis creeping along at a steady 60 MPH.

At lower vehicle speeds, required engine power to simply hold speed (on level roads without wind) drops off so quickly that an Axis at 60 MPH would only need about 60% of the power that it requires at 75 MPH, which means the engine would have to be downsized to around 4.0 liters (versus present 6.8L).

I'm just glad there is still lots of room for improvement. And it wouldn't bother me much to drive slower as long as I didn't get run over.
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Old 10-11-2016, 08:09 PM   #30
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Originally Posted by Chance
Just for the fun of it, I did a little reverse engineering to see what the difference in speed would do if you slowed to 60 MPH (80% of 75 MPH), making some reasonable educated assumptions, and it turns out that slowing from a steady 75 to 60 MPH could bump your fuel economy to around 12 MPG -- provided engine efficiency remained the same. Unfortunately it won't because the V10 is too large to be efficient in an Axis creeping along at a steady 60 MPH.
There are other Axis/Vegas owners reporting more reasonable 9.5+ mpg values (not in this thread, however). My guess has been that they are also driving more reasonable speeds as well (60-65 mph).

My F-350 by itself would rarely go over 11 mpg (also driving 75 mph) which had the 3V V-10 (the same as in the F-53 chassis I believe) and was a little less brick like than the Axis.

What kind of mileage do you get in your van?
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Old 10-11-2016, 09:24 PM   #31
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Originally Posted by JamieGeek View Post

.....cut....

What kind of mileage do you get in your van?
Jamie, as expected, it's also speed dependent, although not to the same extreme as in a motorhome. My 2-valve V10 is proportionally larger than required compared to an Axis, so when I slow down my engine becomes even less efficient (due to low load) which offsets part of what I could have gained.

At +/- 70 MPH I still get close to 15 MPG on the freeway, at 75 MPH it drops to around 14 MPG, and at 80 MPH (rarely do I drive that fast) I only got 13 MPG.

One time I drove at between 60 to 65 MPH to Texas Hill Country and back as a test and got 16 MPG, which was the highest I've ever measured. The van was newer then and didn't need a tune-up as at present.

One difference that helps me a little is that my van has 3.73 gears, which when adjusted for larger tires, would be closer to an Axis having 3.55 gears. But Axis probably came with 4.10 gears or more recently with 4.56 gears, which makes engine run at much higher RPMs. Not that higher RPMs is the main culprit to lower engine efficiency.
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Old 10-11-2016, 10:08 PM   #32
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Aerodynamics are everything when it comes to mpg and RVs don't have it which is why speed kills mpg. Remember you are driving a vehicle that has the aerodynamics of a MAILBOX!!!
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Old 10-11-2016, 10:59 PM   #33
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Just completed a ~5000 trip in out Axis (6 speed). Best mileage was 11.7 and worst was 9.2. Got the best mileage coming out of Yellowstone through the Tetons. The altitude and 45-55 mph speed limit really helped. Most of the tanks were above 10 mpg.
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Old 10-12-2016, 12:13 AM   #34
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Quote:
Originally Posted by Chance
At +/- 70 MPH I still get close to 15 MPG on the freeway, at 75 MPH it drops to around 14 MPG, and at 80 MPH (rarely do I drive that fast) I only got 13 MPG.
The best I ever got on either truck (F-250 w 2V V-10, and F-350 w 3V V-10) was 14 mpg.

Cosmo above provides some better Axis mpg numbers than ours (for slower speeds).

Come on SuperD: A mailbox has a better CD than our RV's!
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Old 10-12-2016, 01:28 AM   #35
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Just got back from a 3800 mile trip from KY to ID and back. Pulled a twelve foot dual axel, enclosed trailer with tools and a 900 pound motorcycle. Averaged 8 mpg at an average speed of 60-65 mpg. However, the mileage would have been better if we hadn't run the generator for 31 hours during our two week trip.
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