Detroit Diesel 60 Series Operator's Manual page 28

Jake Brakes
If your engine is equipped with both
cruise control and Jake Brake
retarders, the Jakes can operate auto-
matically while you are in cruise control.
If the cruise control/engine brake func-
tion is turned on in the ECM program-
ming, the Jakes will come on "low"
when your set road speed increases a
few MPH or KPH above your cruise set
speed. If your speed continues to
increase, the ECM will increase the
Jakes' braking power progressively.
When the vehicle returns to the set
cruise speed, the Jakes will "turn off"
until the next time you need them. For
safety reasons, don't use cruise control
when it's not possible to keep the vehi-
cle at constant speed due to winding
roads ... heavy traffic ... slippery roads
... or when descending grades that call
for Jake Brake assistance.
Shifting
Depending on your transmission model,
the gear split may vary from 500 to 300
RPM. The electronic governor provides
almost no overrun capability; and if the
transmission is downshifted too early,
you will experience a temporary loss of
pulling power until the engine speed falls
below rated speed. In general, when
using a 7 or 9-speed transmission, you
should always downshift between 1250
and 1300 RPM. This is true even on
steep grades with heavy loads. When
using an 18, 15 or 13 speed transmis-
sion, you will need to downshift at an
RPM that allows "less than rated" RPM
before throttle application in the next
gear down. You may want to limit
engine speed to 1900 RPM in all gears.
The Series 60 provides constant horse-
power from 1800 RPM through 2100
RPM, but fuel economy is not as effi-
cient above 1800 RPM.
If you decide to drive at lower RPM's
for improved fuel economy, don't let dif-
ferent engine noises throw you off
®
guard. The Series 60 sounds quiet at
1400 RPM, almost as if it had quit
pulling. Don't believe it! If you had a
boost gage to look at while driving, you
would notice the turbocharger maintain-
ing steady intake manifold pressure,
even as RPM's fall. Depending on the
air intake arrangement, you may also
experience a "chuffing" sound as the
engine starts to pull hard at the lower
RPM's. This is caused by the velocity
changes of the air flow within the air
intake plumbing. Electronic engines can
actually deliver more fuel at lower engine
speeds than at rated speed.
Idling
The common belief that idling a diesel
engine causes no engine damage is
wrong. Idling produces sulfuric acid
which breaks down the oil and eats into
bearings, rings, valve stems and engine
surfaces. If you must idle the engine for
cab heat or cooling, the high idle func-
tion of the cruise control switches
should be utilized. An idle speed of
1100 RPM should be enough to provide
cab heat in above 32°F (0°C) ambients.
A winter front may be used to improve
cab heating while idling, but it should
never cover more than 3/4 of the grill
while driving. Winter fronts should only
be used when the ambient temperature
remains below 10° F (-12.2° C).
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