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Old 07-06-2009, 12:42 PM   #1 (permalink)
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Getting Mileage in a Motorhome

I recently picked up a 21' Class C Toyota-based motorhome. It is a '92 with a 3.0 liter V-6 and overdrive automatic trans. My mileage so far has been 15.5, 17.2, and 15.6 mpg. This is on mostly flat freeways in western Oregon, at around 50 mph. It seems that it is always on the verge of downshifting, and whenever I encounter any grade, I either slow down or it kicks down into 3rd gear. Under slow acceleration it shifts into 4th (overdrive gear) at about 45 mph. One problem is that I always seem to have a head wind. I can tell because I have a little wind sock attached to my radio antenna Actually I watch the flags and trees along the road to estimate wind speed and direction. Does anyone have any experience and/or ideas to improve mileage in one of these? I'd like to have a ScanGauge in it; I suspect that would help, but of course it is not OBD II.
I try to use driving techniques similar to the ones I use to get north of 50 mpg in my '96 Metro, except for coasting engine-off down hills. I haven't tried that yet. I don't know how the automatic trans would like that. I'm also considering removing the rooftop A/C for a little more aero efficiency. It's still got the aerodynamics of a barn door, but overall there should be many opportunities for improvement. All suggestions are welcome, short of melting it down to make a fleet of Prius's.
THX MCH,
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Last edited by Beaver; 07-08-2009 at 01:56 PM.. Reason: Textual error
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Old 07-06-2009, 01:51 PM   #2 (permalink)
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15-16mpg on a 22ft coach is spectacular! My 24ft mini gets 8-9mpg up hill, down hill, towing the boat or not. But that's a 350 Chevy. Not sure what modds could be done since these are tweaked for power now. We're pushing a lot of air! Probably the best bet is technique. Keep it a 50mph, feather it up the hills, back off going down and just sit back a smell the roses! Have fun.
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Old 07-06-2009, 02:31 PM   #3 (permalink)
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If you have deep cycle batteries for other things like a trolling motor, you could set up an alternator kill switch and run off the batteries. Usually nets 10%. More if you can keep the voltage at 14V+

Tire pressure. Are you up to max sidewall? The heavier you are the more rolling resistance comes into play.
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Old 07-06-2009, 02:39 PM   #4 (permalink)
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an Air Dam below the bumper would help a bunch on the highway
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Old 07-06-2009, 03:05 PM   #5 (permalink)
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I used to have a 27 footer with a Ford 460, and it got around 8 mpg. I felt like the ugly American just starting it up (not to mention the price of fuel), so that's why I traded into the Toyota. I have heard of some people who get up into the 18's with them, but talk is cheap on mileage. I trust what is said on this forum, because people here actually run the numbers instead of making optimistic guesses on mpg etc.
The alternator kill switch would probably help a bunch since the coach battery as well as the truck battery are kept topped off by it. I do run the tires at max pressure as indicated on the sidewalls (64 psi), and I always run as lightly loaded as I consider possible. And that air dam idea sounds like a winner too. Thanks for the ideas; I'll give them a try! Any other ideas?
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Old 07-06-2009, 06:17 PM   #6 (permalink)
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Can you post a picture of your rig? The first image that comes up when I do a search for "Toyota 21' Class C" is this:



Looking at this picture, the easy bits would be an undertray and skirts on the rear wheels. More complex might include somehow building a shell into the doors that would allow them to blend into the front of the motorhome body, more aerodynamic (or retractable) mirrors, flush-mounting the marker lights, and making the A/C retractable when traveling (or maybe making a more aerodynamic cover for it while underway.)

As far as the transmission goes, I know that in my Ranger, if I'm on the verge of the transmission downshifting out of overdrive, it's already unlocked the torque converter. If this is the case with you, you may actually get slightly better mileage in headwinds with the selector in 3rd (so the torque converter can re-lock.) A MPGuino or equivalent would definitely help you figure that out. And of course, I don't have to tell you that a manual swap would probably be a good (but expensive) idea.

Finally, you could probably have a small windmill or solar cells that you could use while stationary to charge the house batteries instead of charging them from the alternator while the vehicle is moving.
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Old 07-06-2009, 07:07 PM   #7 (permalink)
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Oh, and agreed; that's fantastic mileage--better than a lot of unloaded trucks.
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Old 07-06-2009, 07:13 PM   #8 (permalink)
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Tire pressure. Tire Pressure, TIRE PRESSURE! Keep 'em hard!

The "Lowest hanging fruit" for you is going to be in the belly pan, rear wheel skirts, and hanging a short frame off the back to make a half-assed kammback type extension. You could call it an "awning", basically.

You could try a partial grille block, but I don't know how your truck would react to that, being a motor-home... all that extra weight to pull around means more load, so you might overheat... couldn't hurt to try, though.
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Old 07-06-2009, 07:23 PM   #9 (permalink)
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90 day: 29.49 mpg (US)

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Zippy - '10 Kymco Agility 125
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Quote:
Originally Posted by Christ View Post
You could try a partial grille block, but I don't know how your truck would react to that, being a motor-home... all that extra weight to pull around means more load, so you might overheat... couldn't hurt to try, though.
Wasn't sure whether I should bring that up. If you go this route, get a REAL water temperature gauge and REAL transmission temperature gauge--don't rely on the dashboard instruments! Also, if that year still has the clutch-driven fan, you could probably benefit from an electric fan swap.
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Old 07-06-2009, 07:58 PM   #10 (permalink)
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Base Metro - '96 Geo Metro
90 day: 54.24 mpg (US)

Neon ACR - '98 Dodge Neon ACR

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Spirit - '92 Toyota Class C Motorhome Winnebago Itasca
90 day: 17.26 mpg (US)
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That picture you downloaded is EXACTLY what mine is, right down to the color and the graphics! An Itasca Spirit, by Winnebago. Tires are the first thing I went for. I pumped them up to the max sidewall pressure before I drove it 2 miles from the seller's home. I could immediately feel a difference in ride; they were pretty low (30 to 40 lbs). Rear wheel skirts sounds like a good easy mod; I could probably use plexiglass. On the belly pan, do you think that should be full length or just under the engine and cab? And would an air dam (which I plan to fabricate and install) reduce the benefits of a belly pan a lot? I am considering removing the roof A/C. It installs in a standard 14" by 14" hole, so it can easily be replaced by a standard crank-open vent. This will not only reduce the frontal area considerably, but it will also reduce the overall weight and lower the center of gravity (thus helping the handling). That's probably 75 pounds way up high, contributing greatly to body roll in corners. I also like the idea of solar panels, given all the surface area I have up on top. That would make an alternator cutout much more feasible, and like you said, it could keep the cabin battery topped off, so I could take it out of the charging circuit altogether, or at least switch it.
And I LOVE the idea of a 5-speed swap! Being a grease monkey at heart, it's just my kind of thing (but it will have to wait a while).
It does have the clutch fan, but it is plastic. Is there a lot to be gained by going to an electric fan over a plastic clutch fan? I'm sure if it was metal there would be. What do you think?
And PLEASE tell me about that MPGuino! It sounds like a gadget that I have to have!
I will probably try a partial grille block; it doesn't seem to have overheating problems. This weekend was the hottest one this year, and I only saw a slight rise in the factory gauge when climbing long grades. Good advice on the "real" gauges too. A tachometer and vacuum gauge are first on my list.
Thanks all, and is there anyone else out there trying for mo-home mileage?
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