Idling vs. turning engine off


#1

My Dad and I just had a long discussion about this. Recently we were waiting in a long gas line at Costco and I would turn the car on and off again to move forward as people moved out of the station. He said that I should leave the car on as the act of starting and turning it off several times creates wear on all the parts involved, while I contended that idling causes sludge to build up in your engine and wastes gas. I eventually was able to get him to concede that turning your car off is better if you’re waiting for someone at one spot, but he still said you shouldn’t turn the car on and off again if you’re in a line. Who’s right here? How much damage is done to your engine while idling and how much is wear is created by turning the car on again?


#2

Turning the car off and on when it is warmed up causes no harm to the motor. The only part that might wear more if this is a frequent habit is the electric starting motor. Assuming this is a modern car with fuel injection, no sludging, no fuel washing down cylinder walls as issues.

Hybrids now, and likely more conventional motors in the future, will have an automatic self shut off and restart feature to save fuel and increase mpg. They will also have beefed up starters designed to handle the more frequent use.

In a fuel line it really depends on how fast the folks are filling up in front of you. You likely saved a thimble full of gas, and put a bit more wear on the starter so it is a wash.


#3
IMO it is just too much work.  If you do enough stop and go traffic you could end up with some repairs that will very quickly wipe out any savings in fuel.   Real life differences will exist, but not likely material.

#4

Many automotive myths still abound, left over from the days of earlier generations of cars that used carburetors and did not have computers hooked up to all those sensors. And so we still get all those father-son discussions about such matters as idling, warmups, oil changes, winter weather, and so on.

In general, it pays to listen to dear old Dad and do things his way when he is in your car. The rest of the time you should use your own judgement, which may or may not be sound. In 25 years or so, you can argue with your own son about his ineffective driving habits.


#5

Turn it off. Idling wastes fuel and costs money. Stopping and starting a warm engine does no harm. The very slight extra wear on the starter is not worth talking about.


#6

SteveF’s 2nd paragraph above is the most important in the long run.

As to the actual question, I believe in letting the engine idle. If you choose to shut it off, then one premature starter replacement can wipe out 10 year’s of fuel savings.


#7

One thing to add: how certain are you about the health of your statrer/battery to start you right up, every time? It’s downright inconsiderate to shut down with the distinct chance of delaying fellow motorists, in the quest of (perhaps) saving a nickel’s worth of fuel.

In addition to starter wear, there’s battery wear, too. A battery can cost upwards of $100, and starting is the largest drain upon it in normal ops. Frequent starting without adequate time to recharge can also “deep cycle” your battery, which is hard on it (sulfation and whatnot).

Despite being a big cheapskate, I don’t shutdown when stopped, unless in a MT stopped on a downward slope (redundant starting setup).


#8

To be fair, it doesn’t seem to me that the OP is talking about something that he does every day. Most people won’t find themselves in that situation often. Therefore, most people probably should turn off their engines in a situation where they are not moving for 5 or more minutes at a time.

Whether to turn off an engine or not should only be a concern if it is something that happens to someone quite often.


#9

Unless you are parked for several minutes at a time, just leave the engine on.


#10

Thanks. I’m usually not in a situation in which I would need to let my car idle for an extended amount of time, but after waiting in the gas line I just wanted to figure out what the trade off is.


#11

Considering engine wear–the more times you restart your engine, the more time the engine spends having to build oil pressure from 0 to normal. While this isn’t much with a hot engine, it probably contributes to wear.

My other concern is with the engine off, that’s a few more seconds that you’re dead in the water if you need to react to a traffic or other potentially harmful situation. I usually shut my engine off if I’m waiting for a long train unless I need the A/C or heat, but having the engine on probably saved the life of an acquaintance–he was first in line at a railroad crossing and someone rear ended him, pushing him through the crossing gate and onto the tracks. He just managed to get his car off the tracks before the train arrived. (This is a dangerous crossing where trains go up to 60 MPH) If he’d shut off his car, he likely wouldn’t have made it.


#12

oblivion has a good point about not overlooking the safety factor. I’ve seen unattended pumps overflow more than once and I know that elderly drivers sometimes go the wrong direction and crash into things, so I’d like the ability to get away quickly if necessary.


#13

Dang! Oblivion’s post about the guy who got knocked onto the R-R track in front of a train sold me!

That said, I don’t turn the engine off when in traffic. I only turn it off when I’m parked, and even then I will sometimes leave it run, like when I’m staying in the car and my wife runs into a store to get one quick item (when it will not run for more than a couple minutes). leaving the engine idle for a minute or two while waiting in traffic never hurt anything, and I do think that it saves wear on the starter.


#14

Unless the waiting times are severe, like more than 5 minutes, I believe it’s better to keep the engine running. It keeps the lubrication system pressurized and eliminates unnecessary wear on the starter system. No damage is done to a modern engine. Modern engines don;t “load up” the way the carburated engines of old did. And “vapor lock” is also a thing of the past, what with the entire fuel system being closed and pressurized from the tank to the injectors.


#15

One time, i was sitting in a line waiting and looking at my tach and it hit me that every minute that went by, I was emitting 3500 liters of exhaust into the air (with a 5L engine idling at 700 rpm. I’m not a tree-hugger but just imagine the visual of 1750 2 liter coke bottles of exhaust times all the cars running. Scary! You’ll never think about it until you sit behind someone with a smoky exhaust and see it all coming at you.


#16

The safety issue is way overstated. I’ve driven over 1,000,000 over 30+ years and not once wold my car running or not have been a safety issue. You’re probably more likely to have a problem due to the engine running and accidentally knocking it into gear or having your foot slip off the brake than you would benefit form being able to react while the engine is running–especially if you are stuck in a line of cars.


#17

dtracy, you’re not taking into account that the intake manifold is under vacuum at idle, so the cylinders aren’t pumping in air at atmospheric pressure, so the volume is much lower.

otoh, if you had a 4-stroke diesel it would draw about 1750 liters per minute.
Remember: a 4-stroke cylinder draws air in every other revolution.


#18

I think Ford is bringing over some Euro tech for it’s 2012 or 2013 model Focus, and maybe more; It’s called Start-Stop. It’ll automatically shut your engine off while you’re waiting, similar to how a hybrid works, and you don’t have to do anything with the car