OPERATION
5-36 / Operating the Engine
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5-16.3 Operation of the High Idle Feature
NOTE: The High Idle feature will be available only when the parking brake is set and the transmission is in
neutral. An indicator light will illuminate when conditions are met to allow high idle engagement.
The optional High Idle (Fast Idle) can be activated/deactivated by a momentary switch, typically found on the
instrument panel, the pump panel, and/or the aerial turntable. High idle is intended for the following purposes:
• Increase alternator output for high electrical loads.
• Increase engine output for high mechanical loads.
• Increase engine speed for periods of prolonged low-load idling when operationally necessary. Refer to “Idling
the Engine” on page 5-35 for important information regarding idling the engine for prolonged periods.
Limit High Idle use to situations that require higher engine speeds to operate accessories effectively i.e. operation
of aerial devices, increased alternator output for electrical loads, HVAC for occupant comfort, or hydraulic systems
for generator or rescue tools.
5-17. Cold Weather Operation
As diesel engines have increased in efficiency, the amount of waste heat available to be drawn from the coolant has
decreased, particularly when operated at idle under a no-load condition. In cold weather with all the heaters
operating, the engine may not reach warm operating temperatures unless it is placed under load.
5-17.1 Cold Weather Pumper Operation
• Ensure that the engine cooler valve on the pump panel is in the closed position. This valve shuts off the flow of
tank water to the auxiliary engine cooler. This cooler is only required during pumping in high ambient conditions.
• Keep the pump panel heater (if so equipped) in the off position when not required. This will draw less heat from
the engine during warm-up.
• Turn the crew cab heater fan to low or off when the crew cab is not occupied. This will draw less heat from the
engine during warm-up.
Because diesel engines are highly efficient, they use very little fuel while idling. As a result, idling in
cold weather will not heat the engine to its normal operating temperature. Operation of a diesel engine
at low idle for extended periods of time can cause engine damage. The following cold weather
guidelines must be followed:
• Avoid extended idling (beyond 10 minutes) whenever possible.
• Use a minimum 45 Cetane diesel fuel or utilize Cetane index improvers from a reputable
manufacturer.
• Maintain a minimum of 1250 rpm idle by use of the hand throttle or high idle system. Always make
sure that parking brake is applied and transmission is in neutral before applying hand throttle.
• Maintain engine cooling system.
• For pumpers: Shut off water flow to the auxiliary cooler using the valve at the pump panel and avoid
the use of pump panel heaters except when essential.
• Use engine block heaters when possible.
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