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Matthew Wright

Is Idling Bad For Your Car?

By February 8, 2009

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To be honest, the question of whether it's good or bad to leave a car idling for an extended time has never crossed my mind. This letter from Deb made me think about it:
As I read the comments about warming up your car, I keep looking to see if it is actually bad for your engine to leave your car idling too long. I've been told that recently, and just wondered if it was true. Thanks for any help and advice you can give! Deb
So, is it bad? I say no. An idling engine that is properly tuned is an efficient machine. If your engine is at operating temperature, your fuel injection is metering fuel correctly, and your exhaust pipe doesn't have a banana in it, there's nothing to be harmed by letting it run. This begs the question of why you're letting your car idle for a long time. It's bad for the environment to pump all those extra hydrocarbons into the atmosphere and you're wasting precious, not to mention expensive gas. I don't think you'll do your engine any harm, but why do it? Give nature a break and turn it off.
February 10, 2009 at 12:10 pm
(1) ol dude says:

I hardly let mine idle very long, it still has a carburetor, and I KNOW polution is greater with carbureted engines; at least thats what the opinions of many seems to be. My question however is: How long should a carbureted engine idle on a very cold morning, or any time after sitting unused for more than 5 or more hours?

February 10, 2009 at 1:48 pm
(2) michael says:

I’m not sure how efficient the burn ratio is when idling but the oil pump is not very efficient when idling.

February 10, 2009 at 4:50 pm
(3) norske says:

I live in North Dakota. I idle my vehicles to warm them up a little in the winter. Either that, or I drive around and warm it up. I don’t shut my engine down until it is warmed up. I see many start a cold engine, and drive a few blocks, and shut it off. That has to harder on it than idling. I have a scooter with sidecar that I drive in town 6 months of the year. So I am still doing my part in helping the environment.

February 10, 2009 at 5:08 pm
(4) Brian Sanders says:

Actually I think if your engine is low on oil may be a little harmful to it. I think it’s also bad on the radiator if You idle your engine too long a time without the car going anywhere especially if You made a habit of it.

February 10, 2009 at 5:15 pm
(5) Loren says:

I would think that it doesn’t hurt the engine to keep it running in the short term.
The longer you leave it running the shorter the life would be. Anything that is working all the time is bound to wear out faster.

February 10, 2009 at 6:12 pm
(6) mred says:

Well I have read the comments and would like to get in my .02 cents worth.
I use 5w30 Mobil 1 oil in my car which doesnt even begin to thicken until you get down to -45 *(F.

however, Here in Ontario it gets almost that cold a few days in the winter and in Northern ontario it does get that cold and a block heater is a must.

I use a block heater on the coldest days and let the engine warm enough to melt the frost on the windscreen and them get into drive it, albeit slowly until the engine gets up to operating temp. after about 20 miles in frigid weather./

My reasoning is this : I use a block heater beacause it eliminates a truly cold start on the engine where engine wear is maximum on cold starts .

I also believe that when the engin eis warm enough to clear the frost off the windscreen it has also warmed up the tranny fluid a bit as well ,as the tranny fluid flows through the radiator.

Using a block heater is energy efficient because electricity is cheaper than gas so the warmup time is not as long as if I used no block heater.

February 10, 2009 at 7:40 pm
(7) Chuck says:

Let me see if I can help shed a little bit of light on this subject. How much idling are we talking about? Gas or Diesel?

If you look in a new car owners manual, you’ll see that extended idling times take your car into the severe maintenance schedule. Police vehicles and taxis are good for this. Reason being, that idling, even with a well tuned, and presice fuel injected engine, you don’t burn all of the fuel in the cylinders. This is why we have EGR, and catalytic systems. Extended idling will cause the unburnt fuel to wash the oil from cylinders, and dilutes oil. The unburnt fuel will also cause carbon deposits on valves, in the EGR system, and cause the catalytic converter(s) to work harder, meaning shortened life. Diesels are known for fuel wash problems(fuel washing oil from cylinders) to the point where newer diesels have an idle up feature that will increase idle and limit fuel if left idling for an extended period of time. These problems become magnified in the cold, because fuel is harder to burn cold.

So, is idling bad.. you could say so.. but then again, these are extreme cases. Most of the time you won’t see the effects of these issues in the time that most people keep there car for. As a fleet mechanic, I’ve only begun to see problems with fuel wash and carbon in high mileage(over 150,000mi.)when iding is an average of 1-2 hours a day. And normally they weren’t the reason that we were working on the vehicle. I don’t think the average person will see a problem with normal idling.
But I completely agree with Matthew, Give mother nature a break. Turn it off whenever possible.

February 10, 2009 at 9:22 pm
(8) Guy says:

Here in CA, idling your car to warm it up is definitely harmful, since our plentiful street thugs are likely to steal and strip it or use it in a crime.

February 12, 2009 at 3:14 pm
(9) Jon says:

Nobody can deny that an idling car is getting zero mpg, but in some cases, idling is better. A diesel motor that hasn’t gotten up to safe operating temperature and is still cold will use way more fuel to start up again, so idling could actually use less fuel.

February 13, 2009 at 6:02 pm
(10) Mark McBeth says:

I do idle my car for three to five minutes in cold weather, around 20 degrees, so the oil has a chance to do it’s job.
I start out driving under 30 mph until I feel warm air coming from the vents and then gradually increase my speed to the desired mph.
I heard that a driven car warms much faster than and idling car.

February 13, 2009 at 9:44 pm
(11) Bill says:

At low outside temps, extended idle times are necessary to save the transmission. If you have to acheive 45+ mph with a cold trans, it will not go into overdrive lockup. If your torque converter is not locked up, your spinning against clutch and steel material. Ask you local trans shop. While your there, ask how much for a rebuild of your specific model.

February 16, 2009 at 12:06 pm
(12) cyantist says:

I understood that some of the lower enginie lubrication is provided by splash from the rotating crankshaft. The reason police cars idling ovrenight to keep warm during surveillance leads to excess wear is poor lubrication. The solution should be to simply rev the engine every few minutes to spray to oil around the crankcase

February 19, 2009 at 3:10 pm
(13) Jon says:

I’ve found that on cold mornings, I start my Durango’s motor and let it warm up with the defrosters going while I scrape the windows. If I take it slow, the few minutes I take is enough to take the next mile to school at the 25 mph speed limit. But then again, that’s just the way the ball rolls in the morning for me, it’d be a complete lie to say I do it on purpose.

February 22, 2009 at 12:52 am
(14) amit roy says:

Idling is bad for diesel engines,as it causes giazing of liner leading to poor engine life.

February 27, 2009 at 2:34 pm
(15) Thomas Watts, Sr. says:

If you are trying to recharge a car battery, you may want to let it idle? This is my situation due to having a small pull against my battery ALL the time.
I know I should fix the problem and not put on a bandaid, but it has to do with wheelchairs. ramps, etc. (Re)charging is the easiest solution. Comments pls on letting the van run for 30-45 minutes for recharging.

March 1, 2009 at 1:40 pm
(16) Marty says:

I see no problem with a idling car as long as it is properly running. It keeps your warm on a cold night during a security shift and you have no other shelter. It will just cost you money for gas for the heat you need to stay warm.

January 4, 2010 at 11:20 am
(17) Minnesota Michael says:

Here in Minnesota, if you don’t idle i.e. warm up your car on a cold day (Which is around 0 not 20 or 30 or whatever Californians call a cold day ;) ) your engine runs very inefficiently. The engine is laboring against the oil, tranny wear is increased due more viscous fluid, and immediately driving a cold vehicle can break belts, hoses, and pumps. If you live where it gets cold, it’s much better to be easy on your car and let it warm up than drive it right away.

January 6, 2010 at 4:29 pm
(18) Gary says:

I have remote start on my 2005 G6, I’ve been starting it up remotely and letting run for 5 – 10 (max the car will run set by the mfg) for 4 years now and so far my car is running like new, but I am not a mechanic.

June 6, 2010 at 1:58 am
(19) CcK says:

It bugs me that nearly every site dodges an actually mechanical answer with “WHY WOULD YOU EVER DO THIS” kind of responses. If you dont know the answer just dont answer! If turning the car off was an option they probably would and if not, I doubt they are smart enough to log onto the internet to make the inquiry in the first place.
There ARE def. reasons why someone would have to do this.
Just a quick example: Police on scene with a dog in the car, Another example: I have to leave my car idle sometimes 8 hours at a time becuase I work security and have to sit in my car all night watching a door or someones work site or whatever and unless the temp happenes to be exactly 68 degrees or something… well idle away… I could list 15 more examples but the point is, just answer the question or move to the next one if you cant so Im not getting 18 emails full of b.s. answers.. it gets frusturating.

July 28, 2010 at 10:47 am
(20) CSRT says:

Thanks CcK, I feel the same way as you. And by idling, its the same thing as when you are sitting in a traffic jam, and nothing magically breaks on your car when you are in a traffic jam. Even a 20+ year old car should be fine when idling, if something breaks int he cooling system, well it was probably under-maintained to begin with and you should have checked it prior to driving.

Warming up your vehicle only helps oil flow by warming up your oil, nothing bad here, idle away!

September 10, 2010 at 2:00 pm
(21) J R Curtis says:

Here in Florida, you have to leave your car idling, with AC on. If not, you will die from the heat! I have to pick my kids up from school and at times, I have to sit in lline for an hour. The only problem is, every now and then the vehicle shuts off when I put it in gear and then it is hard to start. Does anyone know what would cause such? It is a fairly new vehicle and is meticously maintained. Could it be the fuel filter?


November 27, 2010 at 9:18 am
(22) Stefan Vorkoetter says:

Matthew says, “An idling engine that is properly tuned is an efficient machine.”

Say what!?

An engine that is idling has an efficiency of exactly 0%. The purpose of an engine is to produce motion (in something other than just itself). When it is idling, your car is getting 0 mpg, and the engine is producing no usable torque (if it were producing usable torque, something other than the engine would have to be moving – basic physics).

December 22, 2010 at 7:44 pm
(23) Kevin says:

Another valid reason for idling: using your car’s engine as a backup generator. Whenever there is a power failure (once or twice per year), I hook up a power inverter and run it to the house with an extension cord.

January 9, 2011 at 12:33 am
(24) adam says:

it is bad according to Yahoo…

3. Idling hurts the car
According to the Hinkle Charitable Foundation’s Anti-Idling Primer, idling forces an engine “to operate in a very inefficient and gasoline-rich mode that, over time, can degrade the engine’s performance and reduce mileage.”

January 10, 2011 at 12:43 pm
(25) ovi says:

ok ok ok, how about when we take long trips, in very copld contries, sometimes cant afford a hotel and wanna sleep fro 5, 6 hours in the car, you will have to have your engine on, otherwise you will freeze, right?

January 28, 2011 at 9:52 am
(26) steve says:

Idling does cause damage to your vehicle, I dont know how you came to the conclusion that you did. It looks like you did absolutely no research and just let your own reasoning write this article. Idling will make you go through your oil faster which will cost you $ and it causes needles engine wear.

January 30, 2011 at 7:45 am
(27) EN says:

in regards to efficiency from a previous comment, my idling car is very efficient, for what its worth it is being in a constant state of readiness at the lowest fuel cost.
A car also has lights, stereo and a whole bunch of other things that the idling engine powers.
also by definition an “engine” provides power, that in this case is mostley (but not all) used to put the car in motion.

If idling is bad for my engine than so is driving it at all.

Idling is perhaps worse for your battery, with no air flow it gets rather hot in that engine compartment. A 200 degree lead acid battery is not a happy one. just my 2 cents

I leave my 88 Subaru idling 12-48 hours continuous every weekend. it powers my shop and heats it to, then i hop in and drive it to work the rest of the week(its turned off wile I’m at work). it adds about $5 to my fuel cost for the week.

The car has been burning significantly less oil than before being used in this way. 2 years no problems.

Is idling bad for your car? yes, almost as bad as driving it at all!

April 17, 2011 at 11:10 am
(28) paul says:

Long idle periods are done by police, so buying a used police car has always been of concern because of idle time, however, their engines are amazing.

July 5, 2011 at 5:51 am
(29) victor says:

@ Matthew Wright, people that leave in the middle east where the weather is hot, security is in a abundant and fuel is cheaper then water, we tend to leave our cars on while we go in malls for shopping. This is because we want the air condition to keep the car temperature low so as it more comfortable to go in a car and drive it. The temp. goes up to 50 deg C and it would take a cars a/c system almost 30min to bring to around 25deg C temp. and if you car has leather seats then its almost impossible to sit on them as they are real hot. So we do tend to leave our cars on for 30min-1hr while parked during shopping.

Will this damage the engine by doing that. Will the engine heat stress be acted on properly when a car is on idle?

September 1, 2011 at 12:39 am
(30) EN says:

50 deg C, that’s hot, I bet that idling with the AC on full for an hour would overheat most cars. Then if you do over heat your car is running unattended with a boiled out cooling system. That is bad. it would be kind of COOL to watch though.

October 13, 2011 at 2:36 pm
(31) tim says:

I work for a nature gas company and dont matter if its hot or cold if im in the truck its running

November 16, 2011 at 4:00 pm
(32) Jon W. Sharpe says:

Excessive idling will loosen engine by creating slack in pistons and connecting rods. When the engine has drag it eliminates this problem. A little manifold pressure is good.

January 3, 2012 at 11:22 pm
(33) Nick says:

I work in the emergency services field and sometimes my issued vehicle will have to idle for 8 plus hours a day. I have almost 140,000 miles and it stills functions fine without any major mechanical problem. This is a gas engine. I am just glad I don’t have to pay the fuel bill as that does get high judging from all the fuel reciepts I sign for!!!

February 26, 2012 at 3:31 am
(34) Kale says:

I work in the oil patch as a medic. Working 12 hours a day in -20 to -40 weather my diesel mobile treatment centre pickup truck runs most of the time, then I switch off and some one else idles for 12 hours therfore it runs all day. Other than needing frequent oil changes and alot of gas there havent been many other big problems. Only thing I notice is periods of random high idle revving which stops once I press the brakes or touch the gas and i have no clue why.

March 1, 2012 at 4:32 pm
(35) Brad says:

Tons of spelling mistakes. Tsk… tsk…

March 26, 2012 at 4:57 pm
(36) MancalledTribe says:

I work out of my vehicle and my car is constantly running for the duration of my work period witth only small breaks. Ie: if its 100 degrees outside…I keep the AC on …in winter I like to keep from freezing. Even when those rare times when outside temps are very comfortable…..still have to move from place to place. Would love to get a hybrid or something to help cut on gas and pollution …but purchasing one is not in my near future.

May 31, 2012 at 12:21 am
(37) Gil says:

The problem everyone is missing is that my son in law leaves the car running with the AC and lights on while he takes a nap waiting for his wife at work, sometimes for over 2 hours…we live in Arizona where temp reaches 110, now that may add a different perspective to the question.

May 31, 2012 at 9:10 am
(38) Moni says:

If you had a baby that only took naps in the car you’d let it idle too, sorry environment mama needs her sanity… Lol

June 16, 2012 at 10:30 pm
(39) Kim says:

Well, my reasoning behind my questioning lies n the fact, I’m sitting n a double feature drive n and can’t use the radio very long, so I have to idle awhile. I never really got an answer, am I hurting my car or not? Its a nice cool nite, hopefully that’ll help. ????

July 3, 2012 at 9:19 pm
(40) Lisa Scharin says:

I have read in severval different places that idling your car is very inefficient and causes build-up on spark plugs and in the carberator, etc. It is also not running at it’s full capacity, therefore adding runnining time to the engine and harming it.
This is an old article, but I believe that people should be fined for idling for more than 2-5 miunets and that is TOO long anyway. In NYC they have that law and impose it when possible.
With the obvious consequences of our excessive use of fossil fuels and ALL the toxic, dangerous emissions we spew into our air, water & land. EVERY LITTLE BIT HELPS in reducing our use of oil and gas!
I am trying to implement an “Anti-Idling” campaign in Charleston, SC and I hope we can make people aware that Idling GETS YOU NOWHERE and is COSTLY, not only with expensive gas prices, but in the our health and the health of our environment!!

July 28, 2012 at 10:54 am
(41) Paul says:

i ended up here because my power went out due to a storm and it’ll be coming up on 48 hours, i was using my car to power my cable modem and router so i could get on my laptop. thanks for the info

September 26, 2012 at 7:19 pm
(42) michael says:

Thanks to all for the comments. Im about ready to start a taxi gig in central Florida after many years in CA. Being late September its about to cool slowly down but as of now its still very hot, and Ill be waiting at the airport a lot with no shade, and one way or another the engine WILL be idling and the AC WILL be on! Envirnomentally (sic) sound? No. Good for the engine and all its components? Mechanically it would be better if it was at rest, no doubt. Will I sit there drenched in sweat on hot asphalt with the sub beating on the roof? Uh…take a wild guess. Again, thanks to most of you for the common sense.

December 3, 2012 at 12:40 pm
(43) Sam says:

I live in Alaska, it’s -40 out today. I’m letting my car idle ALL day when it’s this cold because there aren’t any plugins at my work. I work 10 hour days, and luckily, I have a car that only burns about 1/8 of a tank idling all day, but as far as harming the engine goes, I have 150,000 miles on my car, and as long as you keep it well maintained, it doesn’t hurt it at all.

December 25, 2012 at 2:36 am
(44) AJA says:

When it is below zero, get a block heater and idle for 1 minute. in normal temperatures idle for 1 minute. Hot climates, idel for 1 minute. Idleing for a long time does NOT hurt your engine. Diesel engins run cool when idling compared with gas engines. Circumstances dictate weather you idle your engines. MOST IMPORTANTLY, RUNING A COLD ENGINE CAUSES MUCH MORE DAMAGE TO THE ENGINE, TRANNY, BELTS ETC THAN IDLING FOR EXTENDED PERIODS OF TIME.

December 25, 2012 at 2:52 am
(45) AJA says:
January 23, 2013 at 9:23 pm
(46) nate says:

idling bad for your car? yes or no!!! who cares I pay for it! I pay for the Costly fuel if i decide to leave my car idle from the day i buy it until the day the engine dies and a rod fly’s through the block is my own problem.

OH and the environment thing until theirs another cost effective way WHITCH THEIR IS MANY but you can thank the power of the oil company to stop all that good stuff from helping out environment. They pump it out i will burn it

May 15, 2013 at 12:00 am
(47) Joseph says:

I leave my car running for more than one hour once in a while, because I make out with my girlfriend in the car, and we need the aircon and music. I definitely hope it’s not harmful for my car!

May 28, 2013 at 1:29 pm
(48) mark says:

I Idle my car all the time for hours to use the a/c. It now has 170,000 miles. and still runs without the pings. I only use either shell, chevron, or 76 gasoline to keep the engine clean, and religiously change all filters, and oil.

August 5, 2013 at 8:06 pm
(49) janice says:

My son has football pratice 5 nights a week in 100 degree weather, I’m not good with heat so I have no choice but to sit in the AC for 2 hours…..I just don’t want to damage my car….I get regular oil changes and tune ups……just worried

November 27, 2013 at 6:38 pm
(50) Caren Geyer says:

I have to sleep in my car tonight cause I don’t have anywhere to stay. How much gas will it use to run my heater?

January 11, 2014 at 8:31 pm
(51) tom says:

i dont drive my 93 1500 much and in order to keep the battery fresh i let it idle for around a half an hour or longer depending on the temp. If it has been below zero then its closer to 45 minutes. I also back it up”forward a few times to make sure tranny and fluilds are beinng runn through the engine.

February 25, 2014 at 10:16 am
(52) Zach says:

When it’s -9 degrees… You kinda gotta let your car run for a bit. That’s why.

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April 15, 2014 at 12:43 pm
(55) Dina says:

my husband wanted to get into house asap one nite when it was raining torrents and somehow forgot to shut off the engine.. in the morning I went looking for the car keys with no luck so went to the car to look and found the car still on.. I shut it off and nothing was smoking or smelling odd so I figured ok but just wanted to be sure it didn’t damage anything for such a long time like from 11pm to 10:30 am next day.

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