The definitive reply is contained in your Operation and Maintenance manual for the engine. The guidelines are set for extreme conditions such that the engine is protected if one follows the guidelines.
Your engine will last relatively longer or shorter depending on how well you abide by the suggestions in the O&M manual.
If it’s not severely cold out and you’re using high quality, clean 15W-40 engine oil or 10W-30 below 70 deg. F, you may start the engine, let it idle for 10-15 seconds and slowly drive away (at modest power levels) with no ill effects.
If running hard or pulling uphill, the engine may need to be run as long as 5 minutes at idle to uniformly cool internal components and reject heat away from turbo bearings; running slowly off the Interstate ramp and driving at low power levels to the fuel stop counts for some of this time, but if running on the highway, it’s a good idea to idle for a couple of minutes before shutting down.
Cummins does NOT recommend excessive idling of the engines, since it can cause excessive carbon buildup on the pistons, piston rings, injector tips, valves, etc.
Over-the-road truckers and bus operators keep their engines running to keep the heaters and/or air conditioning going, however, they run the engines up to about 1200 rpm or so and that will usually keep the coolant temperature in the 140 to 160 range. It still is not recommended by Cummins.
The
belief that idling the engine is better than shutting it down is also a myth.
Idling is not within the manufacturer’s predetermined RPM and load range for
maximum performance and best fuel economy.
When idling unnecessarily, incomplete combustion occurs that causes over-fueling. Under these conditions, combustion gases and fuel can enter the crankcase, causing deterioration to the oil additive package, and eventually cause premature engine damage.
What are some of the Problems Associated with Idling?
Idling Wastes Fuel and Money
• A typical truck burns approximately one gallon of diesel fuel for each hour it idles.
Idling Causes Excessive Engine Wear
• Running an engine at low speed (idling) causes twice the wear on internal parts compared to driving at regular speeds. According to the American Trucking Association, such wear can increase maintenance costs and shorten the life of the engine.
Severe Damage to the Engine’s Oil
• Excessive idling shortens the life of the engine oil at a minimum and may very well make the oil detrimental to the engine.
Unnecessary Idling Causes Pollution
• Idling vehicles can emit significant amounts of pollution including carbon dioxide, which contributes to global climate change; nitrogen oxides and volatile organic compounds, both of which contribute to the formation of ozone smog; poisonous carbon monoxide; and particulate matter.
Idling Poses Health Risks to Drivers
• While sitting in an idling vehicle, drivers are exposed to the vehicle’s pollution more so than when the vehicle is in motion since there is no airflow to vent the emissions.