According to Cummins Customer Support, 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 you’ve been running hard or pulling up hill, 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, before shutting off the engine. When stopping for fuel, running slowly off the Interstate ramp and driving at low power levels to the fuel stop counts for some of this time. If you’ve been 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.
For RV applications, it is recommended that the vehicle be driven for an hour rather than be started and ran at idle for an hour.
Of course idling at start-up will also allow the engine to build up air pressure for the RV’s braking system. Hopefully your diesel RV neighbors have an auxiliary air compressor, so that their engine doesn’t need to be run, to build up air pressure. Especially if they are leaving the RV park at 5 AM.
For more detailed information, visit Don’t Over Idle Your RV’s Diesel Engine.