Don’t Over Idle Your RV’s Diesel Engine

by Steven Fletcher
I don’t know why diesel engines are so noisy compared to gas engines. I’m sure there’s a good reason, I just don’t know what it is. But I do know they’re too darn noisy.

My biggest complaint, without doubt, is diesel owners who idle their engines incessantly, especially at 6:00 a.m. Certainly, most diesel owners are considerate… thank you… but it happens far to often.

In a few cases they really are inconsiderate people but most times these diesel owners think it’s good, even necessary, to let their engines idle for twenty or thirty minutes after startup or before shut down. Truth is, besides being wearisome to neighbors excessive idling can be harmful to your engine.

How Long Do You Really Need to Idle an RV Diesel Engine

I don’t expect you to take my word for it so I emailed Cummins customer support. I couldn’t run the complete reply because it’s too long for this article but here are the key parts:

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.

<snip>…. 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 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; 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…

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. <end snip>

I have received a few e-mails from readers that tell me their motorhome requires as much as six minutes to build up air pressure in the braking system. Here’s my reply.

“You’re right, of course about building up air pressure for your motorhome’s braking system. That issue is not specifically ‘excessive engine warm up’, which was my complaint, but is a reason for idle at startup.

However it’s not an excuse to annoy your neighbors. Especially if you’re one who likes to leave the RV park at the crack of dawn. Many diesel motorhomes have an auxiliary air compressor and so do not require the engine to be running in order to build air pressure. It’s my opinion that responsible owners of diesel powered motorhomes should have auxillury air compressors.”

Now I don’t want you to think I’m obsessed with diesel engine noise or that it’s some kind of cause’ for me… I’m not and it isn’t.

I probably tolerate diesel engine noise as well as the average RVer does.

I don’t hate diesel engines or the people who own them. I accept the diesel engine as part of RVing. But a few RVers have the idea that because their RV came from the factory with a noisy diesel it’s somehow not there fault when they wake the neighbors while leaving the RV park at 5 a.m. I just thought someone should say, it is your fault and you have an obligation to mitigate the noise as much as you possibly can.

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