3508B Engine for Caterpillar Built Machines Caterpillar

The elevated low idle is used to accelerate engine warm-up. The elevated low idle is used to prevent the engine from overcooling when the engine idles for an extended period of time in cold weather.

The engine idle speed is elevated to 1450 RPM when the engine coolant temperature is less than 70 °C (158 °F).

As the engine coolant temperature increases to a temperature that is between 75 to 77°C (167 to 171°F), the engine idle speed is reduced to low idle rpm.

If the engine cools again, the idle rpm increases to 1450 RPM as coolant temperature decreases to 70 °C (158 °F).

The elevated idle map uses 2 °C (3.6 °F) of hysteresis for improved engine stability.

Illustration 1	g01031546
Elevated idle diagram

The elevated idle low idle will be activated 30 seconds after all of the following conditions are met:

• The transmission is in neutral.

• The parking brake is engaged.

• The ground speed of the machine is zero.

• The engine has been running for a ten minute period.

The elevated idle low idle will be deactivated if any of following conditions are met:

• The throttle is depressed more than 25 percent.

• The manual ether switch is depressed.

• The transmission is engaged.

• The parking brake is disengaged.

If the transmission is returned to the neutral position and the parking brake is engaged, the cold cylinder cutout will activate again after ten minutes.