MPG Reality Check

[Pete Masterson]

Considering the topography of your route, that's a trifle low for your 'bird, but not entirely out of line.

My 42' got a low of 4.5 and a high of more than 7 mpg. I noticed that the "best" fuel economy all happened east of the Rockies while traveling in flat places like Texas, Kansas, etc. FWIW, I used 5 mpg for planning purposes and generally got between 5 and 6 on most fill-ups. Hot temperatures (running the generator and ACs), mountains, and high speeds brought the mileage down. Cooler weather, flatter routes, and slower speeds all tended to bring the mileage up.

During the time I owned my coach, I did notice that filling the tank could be highly variable. If the fuel was more "foamy" I might get indications the (300 gal capacity) tank was full when it still could take 30 or 40 gallons more. If the fuel was less foamy, I'd get a much better fill up.

Often, if I'd wait a couple minutes while the fuel "settled down", I could add 20-30 more gallons. So, all the single-tank figures weren't terribly accurate. However, figuring the fuel used over a 2-1/2 year period and 20,000 miles, I ended up with an estimated 5.5 mpg including use of the AquaHot diesel burner (zero mpg) and the generator. The previous owner had calculated the operating hours of these units and had a "pure" mpg figure that put the efficiency nearer to 6+ mpg.

Your rig _should_ be getting something like 7 to 10 mpg if everything was well adjusted and the odometer readings were near-correct.

Pete Masterson

(former) '95 Blue Bird Wanderlodge WBDA 42

El Sobrante CA

"aeonix1@mac.com"

On Feb 12, 2010, at 12:17 PM, freewill2008 wrote:

Finally, after 7 years, I filled the fuel tank to the top, drove 1015 miles, and filled it again. The 167 gallons calculates to about 6 MPG.

The method has plenty of potential for error. The odometer reads low and I don't have a GPS. I used the Google mileage plus 5% to account for wrong turns, finding RV sites, etc. The route was Brookings, OR to Q by way of Hwy 101 and Malibu, CA.

The tank is so big that I figure the fill could be off by as much as 10%. If the fill-up were 10% low, the MPG would have been 6.7. If the fill-up were 10% high, the MPG would have been about 5.5.

Other details: 1984 FC31 with California 210HP turbo 3208. Road speed about 58 MPH. 4.89 gears. 11R22.5 Michelins at 105 and 95 PSI. Towing a Honda CRV. Air filter has about 5000 miles. The air intake is the enlarged version designed for the 250HP turbo engine. Never blows any black unless I make an operator error.

To achieve the 10 MPG sometimes suggested for the FC, my mileage estimate would need to be off by almost 700 miles, or the fill-up would need to be off by almost 70 gallons.

I'd be interested any anyone else's MPG observations and the method used.

Bob Griesel '84 FC31 WLII WA