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Old 09-14-2011, 11:10 AM   #15
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I'm getting 8.0 to 9.0 MPG with a tow and 9-10 without a tow.

It's wind resistance that you're fighting. You'll lose 1-2 MPG for every 5 MPH over 55. Rolling weight math shows the primary reason for fuel efficiency loss is due to wind resistance.

You can help by steady driving, tires inflated, tune-ups, load balance, etc.. but it's wind resistance that's gonna kill your mpg. Especially over 55 mph. I read it's something like 70-80% of your fuel is fighting wind.

Motorhomes are rolling earthquakes and bricks going down the road.

Fleetwood Providence 2008 40e
Ford F-350 4x4 Diesel 6.0L 2006
Honda CR-V 2006
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Old 09-14-2011, 11:33 AM   #16
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My 74 minnie is rated at 5mpg when new.

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Old 09-14-2011, 12:42 PM   #17
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Check tire pressure, filters, alignment, brake drag, steering wander (old rubber bushings, etc. are not your friend).

The HP needed to travel at 70 mph is double that of 55 mph.

Buy a vacuum gauge to mount in driver line-of-sight, and learn to accelerate easily (not dead slow, but slower than you are, I'll bet), and learn to watch it and tachometer versus speedometer. You'll find that a very slight decrease in throttle pressure doesn't change the travel speed perceptibly, but that vacuum readings rise considerably. This will pay cash money.

I would expect 8-mpg on a mechanically well-sorted Class C with a gasser. On the other hand, your fully depreciated MH was cheap enough to buy, so gas mileage is not the $$ problem as with a new one. Put it into perspective with overall costs of ownership.

You can always explore alternatives. One man in AZ has brought his 1995 E350 7.3L diesel Class C to 16 mpg with some aerodynamic mods.

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Old 09-14-2011, 01:24 PM   #18
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Hi Larry,

Don't give up all hope. You'll never even get 10 mpg but I think you can do better than 5.

Lets not forget everyone this is an older engine with a carburetor and it has probably never been touched.

Do your tune up first Larry but your number 1 suspect is that Quadrajet carburetor. They are notorious for developing internal leaks and a warped top casting. The internal leaks waste fuel (duh!) and the warped casting (the top section of the carb) causes a vacuum leak which leaves the jet needles pulled up and allowing full flow of fuel as though you had the throttle wide open. Its a double whammy of fuel wasting and lousy mileage.

Find an old dude who knows how to work on the Q-Jet carb and have him do the proper fixes and rebuild. Alternately, there are new Q-Jet replacements available but you might have to rejet for your engine as the generic replacements are usually jetted for a 350 not a 454.

Best of Luck!
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Old 09-14-2011, 01:28 PM   #19
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Vacuum gauge is good investment. Does it smoke when you start it up after sitting for a while? If so, you probably have a carb with some internal leaks which can really queer the mileage. Bad floats and secondary well plugs leaking were BIG problem with 4 bbl. Rochesters in that time frame.
If it starts hard cold or blows black smke after sitting for 1/2 hour you probably got leaks internally.
hope this helps,

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Old 09-14-2011, 04:24 PM   #20
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You are correct that the carburated engines don't get as good mileage as the later fuel injected versions. However, both versions do best when driving slower. My first RV was a 1977 Midas Mini with a GMC 400 CID V8 engine with a 4 barrel carburator. When driven like a car, it got 5-6 MPG. once I learned to keep a light right foot, mileage increased to 7-8.

Originally Posted by ljedik View Post
I'll admit, maybe my driving habits need to change.I was keeping a steady speed of 65 on the NYS Thruway this past weekend, traveling about 100 miles each way we burned through $140 in gas. (the good stuff) and that was mostly flat except in the Herkimer area.
I even emptied the fresh water tank for this trip knowing that we were going to be hooked up to supply at the site.
I keep an eye on my tire pressure so that is not a factor, I was thinking maybe the age of the RV could be the issue because it is not fuel injected. and it does butn oil a bit. In fact I had to put in two quarts of oil on my way back from the trip to calm her down. Is there anything there I can do?
I will check my weigh limits and see if there is an issue there. We recently remodeled the entire interior and I dont think I used any heavier materials, but I suppose it should get checked.
George Schweikle Lexington, KY
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Old 09-14-2011, 04:47 PM   #21
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Yep... I lower the fesh water tank way down and empty black and gray tanks while traveling.

Fresh, gray and black = ~200 gallons (Black water weighs a little more Hehehehe)..

There's no sense in carrying 1,600 - 2,000 lbs of liquid around.
Fleetwood Providence 2008 40e
Ford F-350 4x4 Diesel 6.0L 2006
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Old 09-16-2011, 03:08 PM   #22
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I guess I can't complain at 8 mpg in my 36 foot wide body. I average between 55 to 60 depending on the hills. I figure why rush, the journey is half the fun.
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Old 09-17-2011, 10:33 AM   #23
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Well, it's a MIdas, every time it pulls into the gas pump the station turns to GOLD don't you know.. Ok, bad joke.

There are several things you can do to improve MPG epically on older rides.

I'm sure you are modifying yoru driving habbits, I mean 80mph just sucks fuel, 55 not so much, so I hope you are already taking your time, I mean the RV lifestyle is not RUSH RUSH, ti's "Stop and smell the roses"

Second a good once over by a compentent mechanic, Now FINDING one these days who remembers how to work on a '79 might not be that easy but they are still otu there,, Look for someone at least as old as your (or to be more specific I) am actually 50 years old and in the business for 30 should do it.

Next.. Check your tire inflation.. now the proper way is to weigh each wheel and visit the tire maker's web page to find the proper inflation FOR THAT WHEEL.. if you need help go to RV Safety, Merritt Island, Florida and click on the weight link on the left side. They do it for a fee and provide the proper chart.

Finally.. This is the week I improve my MPG on good old Poetic.. Twice a year I re-name my Rig Poetic,, then I spend a few days "Waxing Poetic" (I know bad pun) The serious note is a good wash and wax.. not the "hot wax" job at the car wash but a real wipe on buff off wax job, not only does it improve the looks but it improves the MPG.

Used to be a car wash that advertised "A clean car runs better" Turns out.. they were right. I see about 1 MPG improvement in my coach every time I wax.. The first time it was 2MPG (From 8 to 10 MPG) but I"d not done it in a while. Different numbers but the same ratio on the one new car I ever owned.. 16 became 20. That was the full Simonize treatment, Wash, pre-wax cleaner, and hand wax. It felt "Slippery" when I was done. both to my hand, and as it turns out , the air passing by as I drove.
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Old 09-17-2011, 06:50 PM   #24
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Keep in mind that the 454 in a pickup or van would get only about 12 mpg. That's a great deal less frontal area and weight than a motorhome.

I have friends who have 1800 pound hotrods with a 454 and get 3 mpg.

It's all in what you want.
Trucking to support the cats.
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Old 09-17-2011, 06:57 PM   #25
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Originally Posted by wa8yxm View Post

Next.. Check your tire inflation.. now the proper way is to weigh each wheel and visit the tire maker's web page to find the proper inflation FOR THAT WHEEL.. if you need help go to RV Safety, Merritt Island, Florida and click on the weight link on the left side. They do it for a fee and provide the proper chart.
Partly correct: once you find the heaviest wheel position you use that weight to find the correct pressure for all the tires on that axle. You never have different pressures across an axle, all must be the same on an axle.
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Old 09-17-2011, 08:26 PM   #26
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nothing truer then slow down and learn to go light on the throttle at all times
over the months I've owned my mh i have found my right foot can save me money or open a large hole in my wallet.
if i have lots of time and patience i can get 8 if not 5.5 to 6.
but in defense of my mh when we crunched the numbers we spent roughly the same on vacation in the mh as we would have spent the other way and it was way nicer to have our stuff then a hotels.
and my dw panicked over mileage until we figured were she camps is sixty miles round trip, 10 gallons for three or four days of blissful relaxation more then worth the 35 dollars
just my two cents worthhappy travels
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Old 09-18-2011, 11:29 AM   #27
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Our 85 26' Class C with a Ford 460 (carb equipped) got 5.8 mpg at sea level and about 4 in the hills. It had so much smog gear on it, it was a nightmare to work on. I've heard stories that the mid 80s the smog rules got tighter and US manufacturers were scared witless about EFI, so they had to deliberately set the carbs to a richer mixture to give the air injection system enough unburned fuel to work with.

We live in a part of WA that doesn't do smog tests, so I was considering getting a junk-yard carb off an early 70s 429 that wasn't set up for air injection. Then I remembered that my old Colony Park wagon, with said 429, only got about 7 mpg. We disliked that old "C" so bad, we dumped it (at a substantial loss).

We went 6 years without an RV trying to save up to buy a newish one. We finally decided we'd be in wooden boxes pushing daisies before we ever got close, so we mortgaged oureselves again and got our current Class A. It's averaging about 7.2 mpg, and we do a lot of "over the hills" driving. Our recent trip went just over 400 miles including over Stevens Pass (4400ft) on US2 and back over Washington Pass (5700 ft) on SR20.

Initial estimate (haven't gassed up again) says maybe 7.0. We got to stay in Leavenworth, Lake Chelan and Winthrop. Two nights in Leavenworth were $80, two nights at Beebe Bridge, near Chelan was $24 (off-season senior discount) and one night at Winthrop was $30. Add in maybe 60 gallons of gas at $3.75 a gallon, it's still a good value for that trip.

No bed-bugs, our own cooking and we took our remaining Labrador with us.
Frank Damp -Anacortes, WA,(DW- Eileen)
ex-pat Brits (1968) and now ex-RVers, as of 08 Dec 14.
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Old 09-18-2011, 11:38 AM   #28
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When I had my Holiday Rambler with a 454 my best MPG was 8, on level ground at 55mph probably with a tail wind. We calculated travel range at 7 mpg. However, every trip required traveling over a mountain, either the Grapevine, Baker grade, or Oxnard grade. Traveling up-hill I would be lucky to get 5mpg and on the Grapevine 30 mph was wonderful. Our current Workhorse 8.1 engine takes the mountains much better and I can maintain 50mph on the grades, but MPG still remains consistently below 8mpg. Our trip to Portland last month averaged about 6.5 mpg...we really sort of stopped tracking it accurately.

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