Building A Fuel Efficient Jeep Cherokee XJ - Project Mileage Master, Part IIPosted in Project Vehicles on October 1, 2008
In the August issue of Jp we introduced Trasborg's latest harebrained scheme: building a Jeep that can both wheel and get decent mileage on the road. In Part I we dealt with a lot of problems typical of higher-mileage vehicles, put on bigger tires, and started looking at a cooling issue.
Once we got done with that, we turned our attention to the soft underbelly of the Jeep. Unlike Wranglers, Cherokees don't ship from the factory with skidplates or recovery points as standard fare. If you want skidplates, you have to order them, and even then you get some thin, 11-gauge steel that barely covers the vital components. Since we were at stock height, we knew we'd be hitting something important off of some rock sooner rather than later, and decided to armor the Jeep before we damaged it. And it was a fair bet that we'd need to get yanked off of whatever our new skidplate was resting on.
In the last 15 years of playing with Jeeps, we've heard that for every 100 pounds you add or remove from a vehicle, it's like losing or gaining 5 hp, respectively. So we decided to test the theory out. Whatever numbers you subscribe to, it stands to reason that the more weight you add to a vehicle, the more effort it will take for the engine to move said vehicle, and you'll lose fuel economy.
But on a Jeep as short as this one, every bit of armor will help us get off the trail and back home in one piece, so we weighed all the parts we added, and over the last 5,000 miles have been watching what the added weight does to our fuel economy. What we found was that it really didn't do as much as we thought it would.
First 5,000 miles: 15.7 average mpg
Treks belly skid: 60 lbs
Treks stiffeners: 35 lbs
Gen-Right rockers: 100 lbs
Gen-Right gas tank: 60 lbs
Spare tire swing-away and brackets: 42 lbs
Towhooks: 21 lbs
Front skidplate: 18 lbs
WJ seats (weight over stock): 40 lbs
Trailer hitch: 50 lbs
Receiver mount shackle: 20 lbs
Total weight added: 446 lbs
5,000 miles with armor: 15.4 average mpg