What happens to car that idles for an extended time?

A&Q about 350Z
Q:

What do you suppose happens to a car if you let it idle for let's say, 8 hours? Currently it's very much winter here, so I doubt temperature is a problem. But I am curious as what problems could occur if you let your car run at idle for a long time. The vehicle is a 96 Golf.
A:

Idle is when things like oil dilution from condensation and gasoline wash are at their peak since the compression isn't holding much pressure on the rings. For this reason, at idle is when most of the ring "damage" occurs. I put damage in quotes since it is only a very mild effect that just might affect the life of your engine by a very minuscule amount. Its not like idling it for 8 hours will destroy an engine, just that if done frequently it might start aging faster.

As long as you run the engine for a couple hours afterward to evaporate all the junk out of your oil, the oil should be satisfactory but maybe pretty acidic. The problem is that all the stuff dissolved (or emulsified) in the oil will change its properties and that driving you would need to do to evaporate the stuff may accelerate wear on the bearings and cams.

It may cause no damage, but it will be incredibly stressful to the engine. Frequent oil changes would be required, but still without oil analysis you just can't be positive that it will be safe
A:

from what i understand, on some vehicles, they make lower oil pressure while at idle then while driveing. it should be enough to still keep everything lubed and all that good jazz. can i ask why you want to have it idle for a long time? if you really need to do it, i would suggest opening the hood, have a big fan blowing into the radiator, and keep it reved a little bit.

matt
A:

You would also run two other risks that would scare the heck out of me.

If one or both of your cooling fans can't take the constant running and they fail; or if your thermostat decides to stick closed, your next step is replacing the engine. It will continue to get hotter until the pistons and journals will swell up and seize in their holes causing complete destruction of the engine. At this point its even doubtful that it can be rebuilt since critical parts will have gone way out of spec. You will have just made a boat anchor out of a perfectly good engine

A:




Totaly OT, but I know of several engines that have been over heated to the point of seizing, then once cooled down restarted and run again for at least 12months with no detremental effects


One was a Supercharged Toyota 4agze, that was actualy sized twice, allowed to cool and restart and run again. It still held compresion, still handled full boost and still reached for the redline for 4 years afterwards (untill it was sold).



As a general rule overheating an engine till is siezes is an extremely bad idea, and will destroy most engines. But like everything there are exceptions.
A:

I think on some cars, extended idling can reduce the life of the cat. It plugs up because it doesn't get hot enough or something like that.
A:

^^^ Excellent catch, snoopisTDI. I totally forgot that one.
A:

A catalyst won't be damaged because the temperature is too low. At a too low temperature they will stop working tho. A good engine can however heat up the catalyst to operating temperature in around 30 seconds after the engine is started and work even at idle.

An engine usually runs lambda 1 at idle, so gasoline dilution isn't a problem if the engine is warm. If the engine is cold started that will however be a problem and an engine will take very long to reach operating temperature when idling.

The risk of overheating the engine at idle will be very small, if it's cold outside the opposite is usually more of a problem.
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