RV Expert Bruce Bernhart on How to Navigate Steep Grades
in 2008, Motorwatch issued an excellent but little noticed report on how to strategically navigate mountain passes
. I have referred to it frequently. It is a surefire guide to help you successfully climb and descend these roads without brake damage or your engine overheating:
First, it is essential to learn your maximum vehicle speed with the trans- mission in each of the
first three gears, whether your vehicle has a gasoline or diesel engine. It's important because,
if that maximum speed is exceeded on a mountain descent, engine or transmission damage
may occur. To find out the top speed in first gear, place your gear selector into the first range to lock the vehicle into first gear. Then drive it to the maximum rated rpm level on flat and level ground. Repeat this process in each of the first three gears.
Each engine manufacturer rates its engine for the maximum rpms. Check your owner's
manual for this information. If you have a tachometer, it's easy to figure out. If not, you can run
the engine up until it sounds like it is somewhere near the top of its ability (most engine manufacturers today place governors that keep the engine from over revving). Make
note of the maximum vehicle speed at this top engine rpm in each of the lower gears. When you are going down a hill, never allow the vehicle speed to exceed this amount.
Ascending mountains
Lift your foot off the accelerator slightly when climbing a long, steep grade. Watch the
temperature gauges. Lower a gear or two manually if the engine or the transmission is
overheating. If you have a diesel engine and a boost gauge, try to keep the boost below 20 inches of boost pressure to reduce heat buildup. Try to keep the engine rpms on a diesel
engine near the peak horsepower rpms. On a Cummins 8.3 engine without electronic fuel
control, this will be somewhere between 1,800 and 2,000 rpms. On an electronically
controlled engine, this may be closer to 1,600 to 1,800 rpms (you will need to determine where this range is on your particular engine).
The proper gear selection combines horsepower and relatively high engine rpms, which will
help the fan to turn at a faster speed if either a fan belt or a drive that corresponds to engine
speed controls it. A gasoline engine pulls well, somewhere around 3,000 to 4,000 rpm. In any
event, do not press the accelerator to the floor while climbing, as this often causes a tremendous buildup of heat with no significant increase in speed.
A RULE OF THUMB USED BY TRUCKERS IS IF THEY CAN INCREASE THEIR SPEED ON A LONG INCLINE BY PRESSING THE ACCELERATOR THEYRE IN THE RIGHT GEAR
Descending mountains
A frequently asked question is: What gear should I use to descend a grade? For diesel
engines, you may have to downshift one or two gears to safely descend a mountain grade.
For gasoline engines, you can usually descend a grade in the same gear that you would use
to climb it, or downshift one gear. What percent is the grade? Are there any low-speed
curves anywhere on the hill? The book, Mountain Directory for Truck, RV and Motor home Drivers, can help answer these questions. It comes in both Western and Eastern versions
and describes all the major mountain passes, the percentage and lengths of the grades and any lower speed curves. To help plan your trip, read the pertinent information the night before you travel.
RV Expert Bruce Bernhart on How to Navigate Steep Grades
By: Bruce Bernhart
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