Volvo VNL 780 Operator's Manual page 347

Downhill Operation
CAUTION
DO NOT exceed engine manufacturer's
recommended maximum engine speed.
Engine damage can occur. If equipped
with an engine or exhaust brake, DO NOT
exceed 2300 rpm.
On a downgrade, do not coast with the clutch pedal depressed or the transmission in neutral.
Select a gear that does not allow the engine speed to exceed the engine manufacturer's
maximum engine speed recommendation. Use the engine or exhaust brake and/or the
service brakes to control the vehicle speed. A simple rule is to select the same gear used
to go up the grade.
High Altitude Operation
Engines lose power when operated at high altitude because the air is too thin to allow
burning as much fuel as at sea level. Closely monitor the gauges during high altitude
operation. The thinner ambient air reduces the efficiency of the engine cooling system.
Engine overheat or cylinder damage could occur if the engine is operated at full load for
extended periods at high altitudes in hot weather. Downshift and reduce vehicle speed to
reduce engine load when driving on long grades in these conditions. This will help keep
engine air intake manifold and coolant temperatures within safe limits.
OPERATION 337