Fuel these days is expensive. Paying attention to fuel mileage can save money. The challenge comes from driving different roads under different weather conditions while modifying driving behaviors. In the November 2017 Trip Mileage post, we attempted to analyze fuel mileage for a single trip that we had made numerous times in other RVs.
The current challenge is figuring out how powering the refrigerator using the truck’s alternators while driving affects fuel mileage.
The Equipment
The Truck is a 2017 F-450 Dually 4X4 Crew Cab Diesel with Automatic Transmission and 4.30 rear end. The truck has just under 11,000 miles. The truck camper is a 2017 Lance 850 weighing in at around 3,000 pounds. A 2013 Jeep Wrangler Rubicon two door is normally being towed four down. The Rubicon weighs (unloaded) around 4,500 pounds.
The Lance camper’s refrigerator is a 3 way. It can be powered by 12 Volts DC (battery), 110 Volts AC (shore power) or propane. A switch above the refrigerator turns on or off the 12 Volt capability. When the refrigerator is in automatic power mode, when shore power is present that is used. If no shore power, then truck provided 12 Volt power is used when present. Without shore power or truck power, propane is used.
On our latest trip, beginning with San Antonio KOA and ending with What We Didn’t Do On Our Vacation, we sometimes turned on the 12 Volt refrigerator power capability.
Before and After MPG
First off, this is not a scientific study and isn’t repeatable as there are no records of when the refrigerator was running off the truck and when it wasn’t. For a SWAG (silly wild-ass guess), the refrigerator was powered off the truck about ¾ of the time.
Fuel mileage from when the truck was new to around 8,800 miles is 9.93 MPG. These miles were driven before we tried powering the refrigerator using truck power. For the 2,000 plus miles we drove powering the refrigerator using the truck, fuel mileage dropped to 9.25 MPG.
The difference could be ½ a mile per gallon in diesel MPG or more. The average diesel fuel price paid since the truck was purchased is $2.989 per gallon. How much money would running the refrigerator this way cost (9.93 MPG versus 9.25 MPG) on a per mile driven basis? Around 2.23 cents per mile or $223 for 10,000 miles.
Propane Versus Truck Powered Refrigerator
To see which is better, propane or truck powered refrigerator, figure out how much propane can be bought for $200 and compare that to how much propane might be actually used. We have filled a 20 pound propane bottle five times since buying the camper. We have camped in some really cold campgrounds (e.g. Lubbock Winter Camping) using the heat quite a bit. The highest price paid for a propane fill up was $20 in Alpine Texas. At that highest price, we could refill our propane bottles ten times and still come out ahead on propane.
The Safety Factor
Linda says that we should always turn off all propane appliances when fueling the truck. I believe this is especially true for gasoline powered trucks. Less so for diesel powered trucks. The concern is propane ignition in the refrigerator may also ignite gas fumes during fueling. Blowing up a rig would be the beginning of a very bad day. Be careful out there.
For most propane powered RV refrigerators, propane cooling stops working above 5,500 to 6,500 feet elevation. When driving over the mountains, maybe lower gas mileage would be preferable to spoiled food.
In the future, we need to keep better records of when we drive powering the refrigerator off of the 12 Volt system. Then we can more accurately estimate the cost of running the refrigerator this way.
Hope to see you on the road ahead!