Getting Mileage in a Motorhome

[slowmover]

An RV isn't a car. There are those who use them for business. One of my favorites is the old FMC. Built in limited quantity (and high price) in the 1970s. Low ground clearance, independent suspension, low roofline and rear engine. A early Duramax conversion can be worth almost 50% in fuel reduction (gallons, not fuel price). On a rig that was paid for long ago it isn't such an expense given that house is home is car as well. With a concurrent change to disc brakes one is looking at a 30' moho getting 15+ mpg that can travel high speed in safety (65-70 mph).

TheDieselPage has BigRabbitMan's conversion, here.

The choice of coach is more important than the drivetrain, IMO.

[SmellyCat]

Get a roll of black plastic garden trim and screw it on under the front bumper, You can also loosen the kick down cable that goes to the throttle body to the transmission. That may let it hold in gear a little longer on hills. Sc. My apologies if someone already mentioned these

[pete c]

Last week I decided to see if I could carry my canoe on the roof of my Odyssey. It fit up there better than I could have hoped for. I had to prop the front of it up 3 inches using a pair of 2x4s. The front edge of the canoe follows the roof line rather nicely as it curves up (down as it is inverted). Anyway, I took it for a ride and it seemed to work very well. I can not notice any difference handling or drag wise and the more I look at it, the more I think (hope) that a single sleek canoe just might be better than the assortment of smaller bumps (2 max air covered vents and an AC). I will have to do a number of A/B comparison trips to find out for sure. Wish to hell a scanguage worked on a pre-OBD II engine as it would tell me straight away.

[Beaver]

Pete c, you might look in to the MPGuino. I have found it very useful and not too hard for a do-it-yourselfer to hook up. A Google search will get you there, there's also info on them on this website. They do many of the Scangauge functions on pre-OBD II electronic fuel injected vehicles.

[chefdave]

Hi
beaver i have a dolphin motorhome on hilux v6 chassis. im still improving mpg. got a lot of tips from youtech?. Have flushed cooling system fitted new thermostat serviced engine altered timing to 15 dregees btdc and changed auto box oil to dexron 6. Seen mpg go from 13mpg to 16mpg. still waiting to run a full tank without coolent leak etc etc. next on list is to alter vane in airbox and fill diff with a synetic 75-90 oil. then in spring start on aero mods as sub zero temperatures prevent fibreglass from curing.

[Beaver]

Hi Chefdave,
I also use 75-90 in the rear end, and Valvoline Synthetic in the auto trans. I run 5w-30 Mobil 1 in the engine. Have not tried turning up the timing, let us know if you get a ping or overheating, and if it improves your power. I removed the roof A/C for less aero drag. A while back I recently found a Master's thesis online that I have found very informative on the aerodynamics of big rigs. http://publications.lib.chalmers.se/...ext/133659.pdf
It looks at numerous aero devices and analyzes them with fluid dynamics and wind tunnel testing. After reading it I fabricated side skirts and plexiglass fender skirts for my Itasca that seem to be very helpful, although I don't have numbers. I have gotten my average mileage up well into the 18's now, often besting 20, with an occasional foray into the mid-twenties. I think that figuring out the transmission (the MPGuino is VERY helpful for this) helps with MPG as much as anything. The quicker you can get into the highest gear the better, and keeping it there as much as possible is important too. If you're into the 16's you've probably already figured this out. I find that accelerating briskly through each gear (letting off to force a shift to each higher gear as early as possible) and getting it up to cruising speed and into O/D lockup seems to be a good way to do it. On downhill runs, if you can get clear off the gas pedal at speed the fuel cutoff kicks in and shuts off the fuel flow and the instantaneous mileage goes to infinity. You can watch the average mileage climb during this time; it really helps. At a certain point as you slow, the cutoff disengages, If you plan to continue slowing you can click off the O/D, the revs will climb and the shutoff kicks back in. Great for pulling off the freeway. Mainly, the slower you can go at cruise (that allows the use of the highest gear in lockup) the better your mileage will be, all other things being equal.
Good ecomodding, and let us know how it's working!
Beaver

[chefdave]

Hi beaver
no pinging and mid range feels stronger. going up long inclines is a lot easier and takes most inclines in overdrive. Will alter maf vane to make engine run slightly leaner as standard fuelling is very rich.i have kept a log of mileage since day one gone from 13mpg to 16mpg when my tyres need replacing im upgrading to proper van tyres as pervious owner has fitted reinforced car tyres max psi is 45. Engine under pan i will fit a engine sump guard as these are a bolt on mod that smoothd air flow underneath. struggling find smooth lawn edging plenty of corrugated ones.

[pete c]

That MAF mod sounds interesting, but, I wonder if the increased EGTs might cause trouble. You would definitely need to keep an eye on exhaust valve clearances.

I really do need to install an mpguino in the Odyssey so I can test my current mod which is a canoe I carry on the roof. It fits nicely over the AC and max air vent covers. Just had to raise the bow a few inches to keep it from poking a hole in the escape hatch. Escape hatches, btw are just large roof vents that have a quick release latch. Your rig may not have it.

There is another benefit of having the canoe up there. It makes the tarp into a nice dry tent when it is covered at home. Keeps everything nice and dry.

[chefdave]

Hi pete c
i understand the canoe would be the best aerodyamically other than making roof flat.
Thinking of altering my roof line to the same as truck trailers. maf alteration has been carried oit many times check yotatech website. also would like to move exhaust exit from back to behind passenger rear wheel so that i can smooth rear chassis to rear of motorhome body. maybe follow an example from car manufacteruers to make a diffuser. when i get my photo of motorhome uploaded going to use template model to design roof and rear drag reductions body mods. got until spring to design as thats the earlist i can start using fibreglass due to climatic temps. -4c and up to 80mph. winds. joys of where i live

[Beaver]

Chefdave, what is this bolt-on sump guard? Is that a skid plate for a 4-runner? Where would one find such a plate?