freightliner S2 Operator's Manual page 58

Engines
2. Depending on the vehicle gearing, the posted
speed limit can sometimes allow operation in ei-
ther of the top two gears; however, for improved
operating efficiency (fuel economy and engine
life), operate in the top gear at reduced rpm
rather than in the next lower gear at the maxi-
mum rpm.
3.
Cruise at partial throttle whenever road condi-
tions and speed requirements permit. This driv-
ing technique permits operating within the most
economical power range of the engine.
4. When approaching a hill, open the throttle
smoothly to start the upgrade at full power, then
shift down as desired to maintain the optimum
vehicle speed. The high torque of the engine
may permit topping some grades without shifting.
5. Engines are designed to operate over a wide
speed range. More frequent shifting than neces-
sary does not allow proper utilization of this flex-
ibility. The driver who stays in top gear and uses
the wider speed range will achieve the best fuel
economy.
6. The Cummins and Mercedes-Benz engines are
effective as a brake on downhill grades, but take
care not to overspeed the engine going downhill.
The governor has no control over engine speed
when the engine is being pushed by the loaded
vehicle.
NOTICE
Do not allow the engine to exceed its governed
speed, or serious engine damage could result.
7. Never turn the ignition switch to the OFF position
while going downhill. With the engine still in gear,
fuel pressure will build up against the shutdown
valve and can prevent it from opening when the
ignition switch is turned to the ON/RUN position.
8. Use a combination of brakes and gears to keep
the vehicle under control at all times, and to
keep the engine speed below the rated governed
rpm.
9. Check the coolant temperature and oil pressure
gauges frequently.
8.3
NOTICE
Continuous operation below 140°F (60°C), above
212°F (100°C), or with the oil pressure below 10
psi (69 kPa), can damage the engine.
10. Do not idle the engine for more than 10 minutes.
Long periods at low idle can damage the engine.
NOTE: Long periods of idling are not good for
an engine because the combustion chamber
temperatures drop so low that the fuel may not
burn completely. This will cause carbon to clog
the injector spray holes and piston rings, and
can result in stuck valves.
11.
If the engine starts to overheat, reduce the
power output of the engine. Do one, or both, of
the following: (1) Release pressure on the accel-
erator pedal; (2) Shift to a lower gear. If the tem-
perature does not return to normal, shut down
the engine.
High Idle Options
NOTE: To operate the high idle options listed
below, the vehicle must be stopped, the trans-
mission shift lever placed in the Neutral (N) or
Park (P) position, and the parking brake set.
IMPORTANT: Do not idle the engine for exces-
sively long periods. The extreme heat can cause
the bearings to seize or the oil seals to leak.
High Idle with Cruise Control
1. Place the shift lever in Neutral (N) or Park (P)
and set the parking brake.
2. Press the cruise switch located on the dash to
the ON position. Press the RESUME switch to
accelerate the engine revolutions per minute
(rpm) to the minimum set speed. To increase the
engine rpm, press and hold the RESUME switch.
To decrease the engine rpm, press and hold the
SET switch.
NOTE: The rpm can also be increased by de-
pressing the throttle pedal until the desired rpm
is met, and then pressing the SET switch.
3.
Disengage the cruise control by depressing the
service brake pedal, or by moving the ON/OFF
switch to the OFF position.