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Author Topic: Fuel economy on 23 day 2,406 mile Eclipse trip.  (Read 367 times)

garyb1st

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Fuel economy on 23 day 2,406 mile Eclipse trip.
« on: September 07, 2017, 02:59:08 PM »
Mileage on the new motorhome pretty dismal.  Was expecting maybe 8.  We averaged 5.87 before taking into account generator usage.  I think we hit most every grade between the Los Angeles area and Salem Oregon, both going up US 395 and returning between the Coast highway, 101 and I5.  After the Eclipse, we drove to the Oregon coast where we spent a few cool nights.  But because of smoke from a nasty fire threatening Brookings Or, we crossed over the mountains.  More hills from Lincoln city to Roseburg, OR  Then after 200+/- miles south on I5, we returned to the 101 to avoid the heat.  That was a long 4 hour drive along CA 299 with high heat and 4 or 5 construction areas with follow me vehicles.  (I wanted to shoot one guy.  He varied his speed on a long uphill grade between 20 and 30.  Thought I was going to lose the Allison.  Winds on this 23 day trip were not bad.  The heat was.  Consequently for much of the trip we were running with both dash air and one or both roof AC units.  Between dry camping and some very hot days, we ran the generator 78 hours.  When calculating mileage based on generator use, the numbers increase.  If 1/2 gal an hour, mileage bumps up to 6.5.  If 3/4 gph, it's 6.87.  If 1 gph it's 7.29.   

Most interesting was the computer read on mileage.  On one long run from a few miles past Bishop CA, to a few miles before Lake Crowley, approximately 10 miles with a steady grade of about 6%, the computer was reading 2.5 mpg consistently.  If so, that's 4 gallons of fuel to go 10 miles.   Based on the overall mileage, I'd say it was probably a pretty good indicator.  For most of that climb, not towing, I managed 45 to 50 mph.  The motorhome without toad weighs 20,500.  With toad, almost 25,500.  The engine was screaming and hovering around 4,000 rpms.  The engine fan seemed to be doing it's job but the noise level with both the fan going and 2nd gear screaming was pretty severe.  Not sure how to factor in the grades and while we do well on a gently sloping downhill grade, on the steep downhill grades, the grade brake holds us pretty good but the RPM's are in the mid 3,000 to low 4,000 range.  That has to negatively impact mileage. 

 


 
Gary B1st

2005 Pace Arrow 35G
2016 Jeep Wrangler

Paul & Ann

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Re: Fuel economy on 23 day 2,406 mile Eclipse trip.
« Reply #1 on: September 07, 2017, 03:06:45 PM »
Sounds about right.  Do you have the Workhorse, or the Ford chassis?  One snowbird trip, which was about 6,000 miles, we averaged right at 6 mpg which did include generator usage, but I doubt that made a lot of difference in our overall mileage.
Paul & Ann  Iowa
2005 Winnebago Voyage 38J
http://stoughrvadventure.blogspot.com/

garyb1st

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Re: Fuel economy on 23 day 2,406 mile Eclipse trip.
« Reply #2 on: September 07, 2017, 04:29:13 PM »
It's a Workhorse chassis.  Wouldn't be concerned but previous owner lost transmission at 30,000 miles.  Allison is pretty clear about not exceeding the CGWR of 26,000 and we are pushing the limit.  That and the performance tune that bumps HP to 400 and Torque to something over 500 lbs.   Not sure if that is stressing the drivetrain.   
Gary B1st

2005 Pace Arrow 35G
2016 Jeep Wrangler

Charlie 5320

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Re: Fuel economy on 23 day 2,406 mile Eclipse trip.
« Reply #3 on: September 07, 2017, 09:33:24 PM »
Gary my 5500 onan uses about 1 gallon an hour when running both roof airs. On my last 1200 mile trip I never ran my generator and my mileage increased about .8 miles per gallon. Still not very good in my book but it is what it is. This 8.1 don't get the fuel mileage my old 7.4s got, not even close. My old coachs sat about a foot and a half closer to the ground and were about 8" narrower, and 4000 lbs lighter. I've got a K&N filter in mine and am replacing with a wix before my next trip. 
2003 National Dolphin 5320
496  8.1  Workhorse

98 Damon Daybreak 3130
GM Vortech 454  4L80E
SOLD

garyb1st

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Re: Fuel economy on 23 day 2,406 mile Eclipse trip.
« Reply #4 on: September 08, 2017, 10:56:23 AM »
Agree, weight and frontal area are pretty hard to overcome.   
Gary B1st

2005 Pace Arrow 35G
2016 Jeep Wrangler

Gary RV_Wizard

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Re: Fuel economy on 23 day 2,406 mile Eclipse trip.
« Reply #5 on: September 08, 2017, 11:02:26 AM »
Quote
This 8.1 don't get the fuel mileage my old 7.4s got, not even close. My old coachs sat about a foot and a half closer to the ground and were about 8" narrower, and 4000 lbs lighter.

I think those size & weight differences explain the mpg change, not 7.4 vs 8.1L.

As for the genset, two a/c units running is over 50% load on an Onan 5500, let's call it 3000 watts or 55%. Probably a bit more cause the fridge and converter/charger also draw power when the genset is running. Call it 65% load. A late model Onan 5500 consumes about 0.6 gal/hour at 50% load (2750 watts), so I guesstimate about  0.75 gal/hour at 65%. That can easily push your engine mpg down by the 0.8 you mentioned. If you turn off the rear a/c, you would see a substantial improvement in fuel economy.

If you get 8 mpg and drive at 64 mph, you use 8 gal/hour for the engine.  Add in another 0.75 gal/hr for the genset and your total mpg is down to about 7.3 mpg.
Gary
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Gary Brinck
Summers: Black Mountain, NC
Home: Ocala National Forest, FL

garyb1st

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Re: Fuel economy on 23 day 2,406 mile Eclipse trip.
« Reply #6 on: September 08, 2017, 12:31:51 PM »
For most of the trip we were between 55 and 60 mph so don't think that was a major factor.  My guess is the mountain driving which accounted for probably 50% of the trip was the real mileage killer.  IIFC, hwy 299 between Redding and Blue Lake CA get's four mentions in the Mountain Directory.  Many other roads between the coast and US 101 aren't mentioned because the grades aren't long.  Still, they're screaming 4,000+ RPM hills. 
Gary B1st

2005 Pace Arrow 35G
2016 Jeep Wrangler

Kevin Means

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Re: Fuel economy on 23 day 2,406 mile Eclipse trip.
« Reply #7 on: September 08, 2017, 02:47:25 PM »
The V-10 in our previous coach routinely hit 4000 RPMs while climbing 6% grades Gary - and oftentimes higher. The sound of the engine revving that high initially concerned me, because I had never owned a vehicle with an engine that was designed to rev that high, but the V-10 is. In short, try not to worry about it.. it's normal.

We also just got home from three weeks on the road, and yes... it was a hot few weeks. When we were pulling the long grade out of Needles, it was 111 degrees and we were towing. The coolant temp hit 219 once. Whenever my Silverleaf systems monitor indicates that the engine load is at 100% (which is any grade above about 3%) my instant MPG indicates 2.2 MPG, so 2.5 ain't bad!  ;)

As you and the other Gary said, I think your generator-time definitely impacted your overall MPG, and the grades we (seemingly) always have to deal with out here, are really hard on our mileage, that's for sure. The increase we see in mileage when descending grades, never makes up for the decrease we see when climbing them.

Other than mileage, how'd the new coach do overall?

Kev
2011 Winnebago Tour 42QD
Towing a Jeep Rubicon Unlimited LJ or an Acura MDX
RVI Brake 2, Minder TM-66 TPMS, 970 watts of solar
(Can't wait to spend more time RVing)
Lakeside, California

garyb1st

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Re: Fuel economy on 23 day 2,406 mile Eclipse trip.
« Reply #8 on: September 08, 2017, 04:27:33 PM »
The coach handles well.  The dash gauges work some of the time. Periodically the heat gauge goes up as high as it can and just stays there.  We have an OBD reader which gives us a numeric readout.  Typical read is in the 200 - 210 range.  The gas gauge sometimes is at the 9:00 o'clock position.  Not sure if that means we have a tank and a half or what.  This is a Chevy issue.  Dash gauges were replaced once before.  Apparently it didn't take.  But Maria keeps an eye on her phone which has a blue tooth connection to the OBD reader.  At least when she's not playing Sudoko.  Not sure we exceeded 220 but we were close once or twice. 

How was your eclipse trip.  IIRC, you were going to pay dearly for the view.  We were at friends in Turner OR, which was in the path of totality.  One of my daughters drove from Wisconsin to Tennessee only to have cloudy skies.  But as they say, you pay your nickel and you take your chances.   
Gary B1st

2005 Pace Arrow 35G
2016 Jeep Wrangler

Kevin Means

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Re: Fuel economy on 23 day 2,406 mile Eclipse trip.
« Reply #9 on: September 08, 2017, 05:18:43 PM »
We didn't end up going to the eclipse party for which we had reservations. We had paid $340.00 so we could have the honor of being jammed into a parking lot with no hookups! It's a long story why we didn't end up going, but it was fine with me. My plans were to just sit there and supervise the beer keg anyway. Besides, the eclipse would have reduced our solar panels' output, so what would be good about that! 8)

Fortunately, we were able to sell our highly overpriced tickets to my SIL, at face value, so it all worked out (for us). Cyndi and I ended up staying at a really nice Northern Arizona RV park during the eclipse. Didn't see much of the actual eclipse, because we were off-roading in the Jeep at the time. Now THAT was fun!

Kev
2011 Winnebago Tour 42QD
Towing a Jeep Rubicon Unlimited LJ or an Acura MDX
RVI Brake 2, Minder TM-66 TPMS, 970 watts of solar
(Can't wait to spend more time RVing)
Lakeside, California

 

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