Real World Gas Mileage - Workhorse W22 - 8.1 Vortec - Revisited THE GOOD NEWS

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garyb1st

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If interested, here's Tom's old thread.  http://www.rvforum.net/SMF_forum/index.php/topic,120964.msg1104135.html#msg1104135

Just returned from a round trip to the midwest.  Overall, added about 6,500 miles to the Pace Arrow.  Since most of our miles would be in the Midwest, I was looking forward to improved mileage on the Pace Arrow.  That didn't happen. 

For the first 5,783 miles we averaged 6.1 mpg.  With a .6 gph generator adjustment for the 87 hours we ran the generator, the mileage is about 6.45.  Honestly, I was hoping for something north of 7 mpg.  What I didn't expect was the significant winds and rain for most of our trip after we got to South Dakota. 

Now I'm not sure if rain impacts mileage, but headwinds, and from what I read even sidewinds can reduce mileage by 10%.  And the winds on this trip were relentless.  On the return, the worst winds were in northern North Dakota and Montana.  The tall grass alongside the highways was my yardstick.  And for much of the return, they were bent over pretty good.  From what I read, the prevailing winds are generally west to east.  So headwinds or sidewinds for most of the return. 

The other thing I never paid much attention to on previous trips were the rolling hills.  And maybe there were more than on previous trips since we were avoiding the Interstates.  But attempting to keep the heavy Pace in overdrive was a real problem.  Normally I like to cruise around 56 to 60.  Unfortunately with even the slightest hill, it would downshift.  Usually the big Vortec will not upshift into overdrive until I'm over 55 mph.  But on a slight uphill grade, if I'm not cruising at 65 to 70, it will not downshift and then not upshift until I'm over the crest.  That got me thinking that maybe I should increase my average speed to about 65 mph.  So I did, after we were west of Minot ND.  My initial thoughts are that keeping the Pace over 60 - 65 mph probably will not impact overall mileage that much.  However, if the constant upshifting and downshifting are negatively impacting the Allison, then maybe it makes sense.  Also, driving 55 mph on a two lane highway that has a 70 mph speed limit also can be problematic. 

While I haven't figured the mileage on the last fill, I expect it to be exceptional.  From Carson City NV to home is about 420 miles.  I filled in Carson City and while the low gas warning appeared on the dash after maybe 410 miles, the remaining miles suggested another 120 to empty.  That would put me just over 7 mpg without the generator running.  We couldn't get it to run on the long warm, up to 98?, drive home.  So with the dash air running for most of the return, I'd say it wasn't too bad.  However, one major consideration.

The return trip from Carson City involved two major road work areas that overall amounted to maybe 30 to 45 minutes of slow or no go driving.  With significant mountains between Carson City NV and Crowley Lake, CA, and maybe an overall altitude difference of 4 to 5,000 feet, mileage was looking pretty bleak when we stopped at Crowley Lake.  I was thinking it could have been as low as 4 mpg and was hoping for maybe 5.  I'll never know. 

But finally, THE GOOD NEWS.  I've finally figured out the key to better gas mileage.  On the return from Crowley Lake, CA, altitude about 7,000' to our home in SOCAL, about 700', I must have averaged close to 9+ mpg.  So FWIW, driving down hill with no wind is the key to great mileage.  ;) 
 

lynnmor

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I had a similar experience with wind.  Going west my mileage dropped from the headwinds, but as we all know the prevailing wind is typically out of the west.  I was sure that the I would be repaid on the return trip heading east across the top states.  Well the winds changed and I had a relentless wind coming over the starboard bow causing even worse mileage.  The wind was strong enough to kick up dust storms in fields that were visibly damp.
 

Kevin Means

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We just returned from a 3600 mile trip over several weeks, and we averaged 7.2 mpg at 65 mph on the freeways. That's a pretty consistent number for our coach when towing. I really don't sweat the mileage, because it is what it is. It's just something I pay attention to as a possible indicator of something that might be starting to go wrong.

When you consider that we get to visit several neat places, our home, towed vehicle and everything we want or need is with us, 7.2 mpg seems like a bargain. I spent years traveling on airlines and living in hotels, but I'll take RV travel with all its pitfalls any day of the week. I'll bet Gary and Maria, and the majority of Forum members feel the same.

Kev
 

SargeW

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I too would LOVE to see MPG north of  8, but that just isn't going to happen. I'm like Kev, I average about 7.5 without too much headwind and elevation.  But since I have the generator hours and a diesel burner in my Aqua Hot that supplies the hot water in the coach, I probably never will get a solid estimate of MPG. Especially since Diane loves to take long hot showers with the AH supplying endless hot water. 

But I figure since I am "full time" loaded, and weigh in at over 43,000 pounds with the Jeep in tow, I too don't pay too much attention to MPG.  I believe that this is a lifestyle, and you only go around once!
 

Gary RV_Wizard

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Wind resistance is the #1 fuel economy factor in a motorhome. Whether it is natural wind or the wind created by your foot on the go-pedal. Tire friction (rolling resistance) is #2, and that is driven by tire size and the weight they carry.    Climbing hills is a distant 3rd place, but if there are enough of them they start to influence the mpg. Yes, increasing speed just enough to upshift can sometimes yield a net gain.

Motorhomes often get their best mpg cruising on an interstate for long periods. If you can hold it steady on the speed that barely keeps it in top gear (6th on an Allison), the constant speed and mostly easy grades is usually optimum for mpg.
 

Photog

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garyb1st said:
For the first 5,783 miles we averaged 6.1 mpg.  With a .6 gph generator adjustment for the 87 hours we ran the generator, the mileage is about 6.45. 
This is spot on the mileage I have been getting with my 8.1 for years.
 

garyb1st

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Don't disagree Kev and Sarge.  I've been thinking about a diesel, again.  It's something I do every time I head up the US-395 toward Mammoth, June Lakes and beyond Lee Vining.  You're both absolutely right about the joys of RVing.  No matter how you slice it, it's well worth the price of gas. 

So, that said, I'm looking for a new 30 foot diesel, (Maria doesn't want 40+ feet).  It needs a long wheelbase, more than 240", an ISL with 450 HP, 1300 lbs of torque two baths, a minimum 400 sf of space and maybe wings.  Now if I can just find one for the same price of a 15 year old used gasser.

Seriously, I'd love to have a diesel.  And if I could find a well maintained 10 year old 34 - 36 feet, with at least 3 slides, an ISC with 350 HP and a decent wheelbase, I'd be looking to move up. 
 

garyb1st

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Gary RV_Wizard said:
Tire friction (rolling resistance) is #2, and that is driven by tire size and the weight they carry. 

I keep the air pressure in my 22.5 tires at just over 80 PSI.  That based on the mileage charts of Michelin and others.  However, IIRC, the mfg. suggests about 100 PSI.  Should I increase the pressure and if so, how much.  My coach weighs about 21,000 lbs when loaded for travel. 
 

Larry N.

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garyb1st said:
I keep the air pressure in my 22.5 tires at just over 80 PSI.  That based on the mileage charts of Michelin and others.  However, IIRC, the mfg. suggests about 100 PSI.  Should I increase the pressure and if so, how much.  My coach weighs about 21,000 lbs when loaded for travel.
I'm not sure what mileage charts, you use, but the manufacturer's tire inflation charts are based on the amount of weight on the tire. If the table for your tire says 80 psi at the weight you have when traveling, then adding 5-7 psi for insurance (go to 85 or so) is great, just for a bit of margin. Much more than that and you'll get into handling problems from over inflation. Of course all tires on the same axle should be at the same pressure.
 

taoshum

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FWIW, our 40,000 mile average is 9.3 and most of it towing the Jeep.  It's a 5.9/300 diesel though and one of the smaller ones, 34'.
 

SargeW

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taoshum said:
FWIW, our 40,000 mile average is 9.3 and most of it towing the Jeep.  It's a 5.9/300 diesel though and one of the smaller ones, 34'.

Yeah, my first Motorhome was a 2006 32' Meridian. I was averaging 8.5 to 9.5 as well.  Of course it was way lighter than my current Bus, and had 2 slides on the drivers side. But it ran great, and worked well for the most part. We just outgrew it in the full time lifestyle.
 
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