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Indiana Department of Environmental Management

Air Quality in Indiana > DieselWise > Idling Idling

Idling Facts and Myths

Myth: Diesel engines need to be warmed up with long idle periods, especially in cold weather.
Fact: With today's modern diesel engines, engine manufacturers often recommend a warm up time of less than 5 minutes.

Myth: Idling is cost effective because it saves fuel.
Fact: Idling for more than 10 seconds uses more fuel than restarting the engine. In general a heavy duty diesel truck wastes 1 gallon of fuel for every hour it idles.

Myth: It's better for the engine to run at low, idling speeds than to run at regular speeds.
Fact: Running the engine for extended periods of time at low speed (idling) causes more wear on internal parts than running the engine at normal driving speeds.

Myth: The engine must be kept running in order to operate equipment in the cabin (i.e., flashing lights, or radio). This equipment can't be run off the internal circuitry of the vehicle because the battery will run down.
Fact: Such equipment can generally be operated for up to an hour without the engine running before any ill effects on the electrical system will occur.

Idle Reduction Images

Bus Idling Program: You're the Key Sign [JPG]

Clean Air Zone: Do Not Idle Sign [JPG]

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