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LD Gas Mileage
Yahoo Message Number: 3089
We just bought a used 1991 FL/LD with a rare 454 fuel-injected (throttle body) Chevy engine, 22 ft 4 in long. We bought it in Fullerton, CA. Incidentally, we love the LD. Here's our experience with gas mileage in returning to Boulder, CO from Santa Clarita, CA. First, we found out that the odometer and speedometer were both registering low by very close to 10%. How did we verify this? First, my wife followed me in our Volvo which, from previous tests, we know reads accurately within plus or minus l percent. From this we found out the error in speedometer readings. From checking the odometer reading against a 10-mile stretch of mileage markers we determined the odometer reading error. From Santa Clarita to Mesquite, NV we cruised the LD 65-70 mph and obtained 8.9 mpg on 87 octane fuel. Tire pressures were set for 66/56 psi F/R on radial LT225R16 load-range E tires.
Overall average mpg between Santa Clarita and our home in Boulder, CO was 10.3. Between Mesquite and Boulder we averaged 11.3 mpg at least in part by cruising in the 55-60 mph range. Between Glenwood Springs, CO and Boulder we averaged 11.7 mpg on 85 octane fuel partly because of the low cruising speed and the fact that traffic congestion reduced speeds to the 35-45 mph range at times--and because of the mountainous terrain! Interestingly this test, at least, produced gas mileage that was approximately inversely proportional to vehicle speed squared--not particularly surprising since vehicle drag goes up as the square of speed.
Interestingly, the gas mileage occurred over the most mountainous portion of our trip. Over the years this has been the case with numerous vehicles I've owned. I theorize that this occurs because when climbing vehicle speed is reduced so that air drag is reduced and engine efficiency is higher under heavy load. The energy needed to gain elevation is given back when dropping elevation--and when going down hill speed is not so important in achieving good gas mileage as the weight of the vehicle forces coasting with little, if any, need for forward engine power.
In summary, I fully expect to average a good 10 mpg with our LD by generally cruising in the 55-60 mph range or a bit lower. Incidentally, Motorhome magazine tested an identical 1991 FL/LD with a 350 engine in 1991 and achieved similar gas mileage figures.
The article thought the overall character of the LD was very very good with a very balanced set of features. We strongly agree. By the way, we had a set of medium-firm Bilstein shocks installed--and I strongly recommend them. They made a tremendous difference in the ride and handling of the LD. Cost was $500 installed
LD Gas Mileage
Reply #1 –
Yahoo Message Number: 3092
Your note regarding aerodynamic drag is right on.
Colleagues and I at GM put together a math model of RV power requirements.

Aerodynamic drag dominates fuel cost --except for when driving fast uphill.

454 Yum. 502? Yeah.

bob phillips
 
LD Gas Mileage
Reply #2 –
Yahoo Message Number: 3102
Our '83 350 gets 6-7 mpg driving in those same mountain conditions. The difference is fuel injection.
 Driving on the flat near sea level at 65 mph we will get about 9 mpg.

Steve
2004 FL
2013 Honda Fit