How bad is it to let a car idle for too long?

Question

I've heard that it isn't good for a car for it to idle for too long. I was making a cross country (U.S.) drive when I moved. I didn't sleep well one night, and was sleepy during the drive the next day. I was drinking caffeine. But I stopped at a rest stop and took a nap. It's in the middle of the winter, and I'm driving through Utah at the moment, so it's freezing. I wound up sleeping for a while, running the engine for a few moments every now and then to warm the car up. I was using my cell phone as an alarm clock. But I was so tired that I wound up dozing off while the car was actually running, and it ran for a couple of hours. I learned my lesson about sleeping in the car in the middle of the winter. I should have just called it quits that day and found a motel. But it's too late for that. My car doesn't normally idle much. I don't go through many drive thrus, and I'm not usually in gridlock traffic. So how much damage could have been done to my car by it idling like that? Thanks!

Answer 1

There is a problem with letting a car idle for too long.  It can damage the catalytic converter which can cost £1000 to replace.

The problem comes with the throttle plate.  This is effectively a valve that opens and shuts in the intake manifold and regulates the air flow.  It is attached to the accelerator/gas pedal and when the pedal is pressed, the throttle plate opens proportionally.  When you floor it, the throttle plate opens 100%.  However when you don't touch the pedal i.e. let the engine idle, the throttle plate almost closes- but not quite (or the engine will stall).  It is only about 3% open.  Under these conditions the engine has to act as a pump, effectively forcing air through in order to run.  

The lack of air means the engine will be using much more fuel to run  (ever wondered why you use a lot of fuel while in a traffic jam?) and this richer mixture can clog up in the catalytic converter.

If you have to leave the engine idling for any length of time then take the car for a blast down the motorway/freeway and let the engine rev to 5500-6000rpm so the unburnt fuel deposits will be blown out of the system- you will see a cloud of black smoke coming from the exhaust.  This is a good sign and will hopefully save you the cost of a new exhaust.

Apologies if this sounds a bit long winded.  The chances are your car is okay.  If you HAVE to let it idle for long peroids, just remeber to drive it hard afterwards.  Happy christmas.

Answer 2

It is very unlikely that you could cause damage to your car by letting it idle.  In fact, in cold conditions, it is probably wise to let the car idle for some time to warm up the interior.  Make sure that each time you start the car in cold conditions, you let it idle for at least 10-30 minutes, to make sure you don't end up with a dead battery from repeated starts.

Regarding the catalytic converter, it is very unlikely that you would cause damage by idling the vehicle.  Furthermore, it should not cost more than $200-300 to replace, and is a part that has a finite lifetime anyway.

Bottom line?  Not much damage.

Answer 3

Dont worry, idling can actually help sometimes, even for long periods.  What you did was very good, to pull off and get rest.  I drive an 18 wheeler and sometimes we idle for comfort, and during extreme cold to keep the engine and fuel from freezing.  Now idling a diesel engine is actually not really good because it does cause a build up of soot, but gas-burning vehicles has a much less build up of soot, which is caught in the catalytic converter (and a normal process).  I repeat, no damage was caused and its good that you pulled off to sleep rather than driving sleepy.

Another point is everytime you start a car it takes battery power ESPECIALLY more during winter, meaning its better to leave the automobile idling rather than shutting off, turning on, then shutting off etc....

Answer 4

pollution and you are buring gas at $3.00 and over a gallone. diesel can idel and does not pollut quite as much

Answer 5

No Damage whatsoever.....engines are designed to run, doesn't matter if it's idling or on the highway...provided the cooling system is workng properly and most importantly the exhaust system is in proper operating condition so as not to asphyxiate you while your sleeping... You woke up so I believe it was in good working order...

Think of Police cars, they idle for long periods and then when a call comes over the radio/computer they speed to whatever scene or traffic stop they need to respond to....Then repeat the proccess, then they are retired and become what?...Taxi Cabs, where they idle for long periods and are driven by luniatics.....LOL

Don't worry, your car will be fine....