Idling your vehicle, which some people may want to do for charging the batteries, keeping warm, or keeping cool, should be avoided if possible. It wastes fuel, may create dangerous exhaust buildup, and adds wear to your engine and alternator. The extent to which idling damages your vehicle is the subject of some debate; some say not to worry about it at all, while others say to never idle. However, your vehicle is likely among your most expensive possessions, so it's generally a good idea to treat it as nicely as possible. If you are idling your vehicle every day, you should look for alternative options.
Health risks
- Never sleep with your vehicle running!
- Idling could result in CO poisoning (a carbon monoxide detector is a must-have!), especially if your exhaust is blocked or damaged (such as by snow.
- Newer vehicles generally have cleaner, safer exhaust than older vehicles.
Hybrid vehicles
If you have a hybrid (gas-electric) vehicle, you may be able idle your car for power, since the engine basically functions as a generator during normal use, so it can generate plenty of electricity without engine damage. Check your owner's manual and follow guidelines.
Stealth
Idling your vehicle calls attention to your vehicle and destroys any stealth you may otherwise have had due to:
- Engine noise,
- Daytime running lamps, if present and not disabled, and
- Visible exhaust plume in cold weather.
Vehicle damages
This can have serious effects on the vehicle's engine:
- Idling for one hour every day for one year is equivalent to 64,000 miles of engine wear.[1]
- Other sources say idling one hour is equivalent to driving 25 miles.
- Idling accelerates engine wear and tear creating a need for more regular maintenance and an increase in the number of oil changes.[2]
- Because the engine is not operating at its optimal temperature when idling, fuel is only partially combusted, leading to fuel residue buildup on the cylinder walls. This can further damage engine components, including spark plugs and exhaust systems, increasing maintenance costs and shortening the life of the engine.[3]
- Direct-injected gasoline engines can be carbon-fouled by idling.
Alternator damage
Idling to charge is hard on the alternator. Alternators are typically only ~50% efficient. When the alternator is pumping out 500w for your use it is also creating 500w of heat, cooking itself. The easiest way to avoid excess alternator heat is only charge from the alternator while driving (engine rpm ~2,000). This has multiple effects:
- the alternator spins fast enough that its own cooling blades become effective, and
- the alternator is running at its most efficient RPM (~6,000)
- airflow from the forward motion of the vehicle helps remove heat from under the hood
Idling cautiously
If you idle your vehicle, here are some steps to reduce chances of a Bad Outcome:
- open the hood to allow excess underhood heat to escape. Sun should not shine directly into the engine bay.
- point the vehicle's grille into any breeze, if present
- if there is snow, ensure that your exhaust pipe is not blocked and exhaust can safely move away from the vehicle
- watch for red flags: hot smells, belt squealing, engine RPM dropping significantly, chassis voltage falling from normal levels (14.1v, or whatever you observe without charging), or the charger reporting less current than usual, if applicable.