Idling is for Inconsiderate Knuckleheads

Dear Car Talk

Dear Car Talk | Jan 09, 2014

Dear Tom and Ray:

I manage an RV park but know nothing about diesel engines. Why does everyone who has a diesel start and idle it for 30 minutes before leaving? Even people towing nothing but a small trailer do that every morning before they leave. Why?

-- John

TOM: Because they're inconsiderate knuckleheads, John.

RAY: There's no reason to idle a diesel engine in an RV for 30 minutes before hitting the road.

TOM: In all weather but extreme cold, most diesel-engine manufacturers recommend idling the engine for 10 to 15 seconds before driving away gently. That's SECONDS!

RAY: Now, some RVs have air brakes and need to build up pressure in the braking system before driving away. But that also takes no more than about five minutes. Not half an hour.

TOM: And lots of those RVs have (or should have) what's called an "auxiliary air compressor" on board, which instantly gives the brake system enough pressure and eliminates the need for idling.

RAY: Even if someone left his or her lights on, or otherwise drained the battery, it's still better for the engine to drive the vehicle for an hour than to let it idle for an hour.

TOM: Cummins, for instance (one of the major diesel engine manufacturers), warns in its owner's manuals that excessive idling of the engine can cause carbon to build up on the pistons, piston rings, injector tips, valves and more. Which leads to expensive repairs and shortens the life of the engine.

RAY: So, not only is it not necessary, it's actually harmful!

TOM: So if early risers at the RV park don't care that they're throwing away $4-a-gallon diesel fuel, polluting the pristine nature they've driven a long way to enjoy and annoying their formerly sleeping neighbors, perhaps they'll be motivated to stop this dumb practice by being alerted to the fact that they're actually harming their engines, not helping them. Pass the word, John.

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