subject: RV Expert Bruce Bernhart on the Use of Cruise Control in Hilly Terrain [print this page] This is a continuation in my summary series based on an in-depth report that was issued by Motorwatch in 2008 on the proper navigation of steeper grades in your RV. In this article, we summarize the highlights of proper operation of the cruise control. The cruise control is a wonderful device that can help you maintain a steady, consistent speed. However, cruise control is less effective, and even dangerous to use, in heavy traffic or in other situations when speeds change frequently.
Downgrades
Never use your cruise control to help maintain speed on a steep or long downgrade. Many of
the earlier cruise control systems were designed to utilize only about 80 percent of the throttle
or accelerator capability. On occasion, the system doesn't allow the accelerator to go to the
full fuel or come back to the no fuel positions. On a steep grade, those vehicles equipped with a diesel engine wouldn't engage the engine or exhaust brake. Owners of later vehicles
equipped with electronically controlled fuel systems and throttles don't have to be concerned
with this problem. Remember, you may have to downshift one or two gears in your motor
home when encountering long downgrades. Descending a long hill with the brakes pressed all the way down creates a buildup of heat sufficient to cause warping of the brakes, resulting in a pulsing of the brake pedal.
Long Upgrades
Contrary to popular belief, cruise control can be advantageous when climbing long, gradual
grades. If you can find a speed somewhere near the proper climbing rpm range, and the
grade is fairly consistent, cruise control will maintain the chosen speed more efficiently and economically than you can with your foot.
If you have a diesel engine and a boost gauge, you can use this procedure: Maintain the
same speed at various throttle positions. The further you push it, the more fuel is consumed.
You probably won't increase your vehicle speed by one mile per hour. Lower boost pressure means less fuel consumption. If you have a gasoline engine, you can check this by installing and observing a vacuum gauge. Low numbers mean more fuel consumption; high numbers, less.
Hilly and Mountainous Countryside
Cruise control is not very effective in hilly or mountainous terrain. To maintain the preset
speed going downhill, the vehicle will be close to the no fuel throttle setting until you actually
start up the next hill. Then it will go to almost full fuel. In the meantime, you'll lose your speed. Control your speed manually with your foot on the accelerator in hilly country.
According to the Oregon Highway Patrol, one motor home per week burns to the ground while trying to climb Cabbage Hill on 1-84 east of Pendleton. Since upgrades can be taxing on a
vehicle, it's important to control your shifting so your vehicle does not overheat. It's also vital to your safety to keep your brakes from becoming too hot while descending asteep grade.
RV Expert Bruce Bernhart on the Use of Cruise Control in Hilly Terrain
