How bad is it to sit in my car for an hour while it’s running?

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chibi78@reddit

If everything is ok with a car you will be fine

Did like a 30 minute drive and immediately had to lay down and pass out, dizzy with the worst headache

Realized I probably could’ve died if it was much longer

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Yup. When I need to sit in the car for extended amount of time.

Western-Bug-2873@reddit

Higher amount of emissions when idling? Tell me you know nothing about physics without telling me...

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H3LL0FRI3ND_exe_file@reddit

When a car is idling, the engine is running but not doing any useful work (no movement, no load). That situation makes it less efficient compared to when the car is cruising steadily. Here’s why emissions can be higher during idling: 1. Poor fuel–air mixing at idle • At low RPM, combustion isn’t as clean or complete. • This can increase carbon monoxide (CO) and unburned hydrocarbons (HC) in the exhaust. 2. Catalytic converter not at peak efficiency • The catalytic converter needs heat and steady exhaust flow to work at its best. • At idle, exhaust gas is cooler and moves more slowly, so the converter removes fewer pollutants. 3. Higher emissions per distance traveled • Even if the engine isn’t spewing huge amounts per second, the car is moving zero kilometers. • That means emissions per kilometer skyrocket at idle, because you’re burning fuel but going nowhere. 4. Engine design trade-offs • Engines are tuned for efficiency at cruising loads, not for sitting still. • At idle, air–fuel ratio and spark timing are adjusted mostly to keep the engine running smoothly, not to minimize emissions. 5. Older vs newer cars • Modern cars with start-stop systems reduce idling emissions drastically by cutting the engine when stationary. • Older engines (especially carbureted ones) tend to dump a lot of fuel when idling, making emissions far worse.

👉 In short: idling burns fuel inefficiently, produces incomplete combustion, and delivers high emissions per unit of distance.

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Western-Bug-2873@reddit

Yeah, you seem to be going off of data from 1974.

Modern cars have very complex electronic engine control systems to control air-fuel mixture and exhaust emissions down to an extremely fine degree. Catalytic converters are close coupled to the engine for fast light off and efficient low speed operation, and heated oxygen or air/fuel ratio sensors begin reporting and achieve closed loop often within seconds of engine startup.

Obviously a stopped car is getting no fuel economy vs driving down the road, but to say that it is polluting more just because it's idling is patently false.

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H3LL0FRI3ND_exe_file@reddit

Fair point. Modern ECUs, close-coupled catalytic converters, and wideband O₂ sensors have drastically reduced how dirty idling is compared to older engines. Once the cat is lit, emissions at idle are indeed very low.

That said, idling still isn’t emission-free. A warm modern car typically burns around 0.6–1.2 liters of fuel per hour at idle, which means continuous CO₂ output and some residual CO/HC/NOₓ. And if we look at emissions per kilometer, idling is technically the worst case since you’re producing pollutants without moving at all.

The one situation where idling definitely pollutes more (even with modern controls) is cold start, because the catalyst hasn’t reached light-off temperature yet. That’s why most manufacturers recommend driving off gently instead of warming up the car by idling.

So I’d put it this way: modern systems mean idling is far cleaner than it used to be, but it’s still wasteful and not emission-free, which is exactly why start-stop systems became standard.

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main_topsail@reddit

Yup - this person motors. As someone who does my own car maintenance and repairs, this matches my experience.

Makes the mpg worse but the car isn’t performing worse it’s just running without going anywhere so you get literally 0 miles per gallon, hurts the average a bit

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Sparky62075@reddit

just made my mpg about 3 miles worse

This can happen to any car at 186k miles. Cylinders will have slightly less compression, crank and/or cam shafts can get worn, gaskets can start to leak. These things don't get fixed with regular maintenance.

uh-huh--honey@reddit (OP)

Ok honestly was not expecting smart but simple financial advice from car guys but I’m loving it. Is this what it’s like growing up with a dad?

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VioletCassidy@reddit

It's like growing up with a mom, in my case.

There is absolutely a reason to be doing it. Oil not only lubricates your engine but it traps dirt and carbon buildup. With how thin oil and oil galleys are in modern vehicles I strongly discourage anyone from going above 5000 miles on a synthetic.

Source : Am an automotive technician.

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ImpostureTechAdmin@reddit

Home boy, I'm talking about having lab work done on the oil before raising the interval, they test for all of this. You're a lube tech that's never done oil analysis on precision engineering I guarantee it

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Itchy_Winner_7903@reddit

I get exactly what you are saying, I just don’t really see the reasoning for it.

SoftCattle287@reddit

That’s pretty pricey. I get oil and filter for roughly 35-40$ and do them myself. And I’m not saying 3k intervals like conventional oil but 5-6k has been my go to. And I’ve had no issues. And damn 14k intervals. I don’t know if I’d trust that unless I was using top tier oil and filter like ams oil. But that’s me. Also never had to take oil pan or valve cover off to notice any sludge so who knows 🤷‍♂️

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B5_S4@reddit

It's a German car, I run liqui-moly and mann filters, and even at 14k I've never had Blackstone report that I had used up all of the additives in the oil.

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ProfessionalKick8487@reddit

Yeah OK. I use Liquid Moly in my Mercedes and change it at 5k miles. This is the first time I've heard of Blackstone oil analyst to check your oil. 30 bucks. I can look at the oil on the dip stick and can tell the condition of the oil. Anyone can take it into consideration it depends on how the car's driven conditions matter. My Mercedes I change at 5k I drive the car really hard and in the summer months the oil breaks down faster. Say it ain't true.

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B5_S4@reddit

ImpostureTechAdmin@reddit

Kias blow up no matter what. Friend of mine worked at a dealership and said 60% of their warranty work was engine replacements. They fail in ways unrelated to oil health

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theyeastwrangler@reddit

True but they’ll be replaced with Kia’s money as long as you go by their recommendations for oil changes and it’s still under warranty. If you don’t change it every 5k-7k miles like the manufacturer recommends then that’s on you

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ImpostureTechAdmin@reddit

If you don’t change it every 5k-7k miles like the manufacturer recommends then that’s on you

https://www.kia.com/la/discover-kia/ask/how-often-should-i-change-the-oil-in-a-car.html

NewYearNewAccount165@reddit

Thats your personal use case. To make a blanket statement that everyone can go 10k+ is wrong

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randall_savagery@reddit

I drive a diesel. The oil life of diesel is low compared to gas burners. This current generation of oil coupled with the current engines make the shelf life ridiculously high.

dbear496@reddit

Does this "little computer" actually measure oil health, or does it just measure the length of time since the last change. I've only ever heard of the latter.

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Icy_Inevitable714@reddit

It’s more than just length of time, it’s a number of factors including distance driven, speed, acceleration, temperature, and possibly other things depending on the manufacturer. In the past your owners manual would have a scheduled interval for when to change the oil, nowadays the manual just says “do what the computer says” and I think it’s safe to say the engineers behind these cars know what they’re doing

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Camo138@reddit

As I found out a second engine for my car is like $6k. That's before the cost of install

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Sparky62075@reddit

What kind of engine, and what kind of car?

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SpiketheFox32@reddit

5k? Ain't nobody got time for that.

ProfessionalKick8487@reddit

True. Direct injection motors scavenge unburned fuel and also they cause carbon build up in you motor

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Less-General-9578@reddit

if you have a Turbocharger, make that change at 3,000

and why would most people want a Turbo, they are not durable and introduce more problems than naturally aspirated engines.

unless you don't care and money no object. groan.

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8_bit_femboy@reddit

Brother i have had 4 turbocharger cars and all were changed at 2 years/20k miles, as per manufacturer reccomendation (as have everyone i know basically), never a single problem. Stop being paranoid. Where i am 5 quarts of high quality oil costs 60-70 dollars, and a good quality filter 20. One of my cars is at 280k miles right now. Now lets say 65 dollars for oil, 20 for filter. 270/2085=1150 dollars. 270/385=7650 dollars. so stop saying this shit oil is cheaper than an engine. At this point i can buy a new turbo, which isnt showing any signs of breaking, or install a used engine, or have 6k dollars for a used beater... and no its not a one off, in europe seing very high mileage cars with 20k or even longer intervals is very very common...

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Less-General-9578@reddit

actually oil is cheap at Walmart if you buy Super Tech synthetic. where do you buy 70 dollar synthetic oil from ? do you change your own oil?

a 20 dollar filter, try the Super Tech filter for about 4 bucks and change at 3k miles. these filters are very well rated at that 3k mileage.

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wtfisasamoflange@reddit

Yeah I'm going to say you're wrong on the not durable part. They have made huge improvements with fuel economy due to having smaller capacity engines with an added turbo system. Newer turbos do not have the same issues either as they have solved a lot of cooling problems, which is what made them not durable. You don't need a 'turbo timer' anymore since the car automatically pumps coolant through the housing when you turn the engine off. There are lots my good chum.

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duuchu@reddit

4000 miles in 6 months is way less than the average 15k a yeR

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Substantial_Team6751@reddit

Six months maybe if your car is from the 1970s and has a carburetor. With modern fuel injection there is very little unburnt fuel in oil.

I've watched various test videos that show that synthetic is still sitting in a crankcase for a year or even two.

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Au-contraire...

Your "common sense" is not intuitive...

There are a frig-tonne of variables when it comes to engine wear. Most engines are not designed to run at idle, so often they have lower oil pressure at idle for efficiency reasons. Cop cars? Designed to live at idle.

Go to a truck stop anywhere in the world, and any truck sitting overnight will NOT be at idle. They are either not running on the main engine, or the engine is at "high idle," meaning instead of running at 600 rpm, they are probably running at 1000 rpm.

When a car sits at idle, the oil pressure is quite low, and the alternator does not even provide enough power to charge the battery.

You are putting the equivalent of an hours drive of wear on your engine with the added benefit of probably not adequately oiling the camshaft and lifters.

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StuffIanWrote@reddit

Ford came up with that number. I did a quick Google search for a link, but ran out of time before I had to leave for work.

I believe it’s in at least one of their documents discussing service schedules. Check the ones for Police Interceptor models, perhaps.

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ChrisinOrangeCounty@reddit

My car is a plug-in hybrid, so it doesn't do anything except use my big battery.

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Paper-street-garage@reddit

Bad for our air and planet and it uses way more gas than you think.

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notalottoseehere@reddit

Had to leave the car running for 4 hrs in 35°C heat while I got a new tyre (old dog couldn't handle heat). Car was fine. Car is 6 years old...

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Mike312@reddit

One time for 4 hours is one thing, doing it daily for years is another.

OP is adding a 3rd heat cycle to their engine every day, wasting probably about a gallon of gasoline.

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Habatcho@reddit

Ive done it upwards of 10 hrs a day for the past 5-6 years and my cars have never had an engine issue minus a head gasket leak at 130k which I drove on for 6k miles without having to refill despite them recommending an engine rebuild.

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notalottoseehere@reddit

Yep, I was nervous, but was only a one time thing.

Generally, I never idle the car. It's a hybrid, but still.

If it's an electric car, you'll be fine until the battery runs down, but that would happen with you run out of gas with an ICE too.

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pink-starburstt@reddit

i do this every day lol. also went like 2k miles over the oil change indicator went on. 2023 honda accord hybrid. i suck at cars and its fine

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spkoller2@reddit

Your car has this thing called a radiator. It’s to cool the engine with liquid. The liquid is cooled with airflow through your radiator

When you use the engine without the air cooling it will wear the engine more. An electric fan may come on now and then but my experience was this means your engine is hot

If you have a turbo, an older VW, a big sports engine, a Harley… idling is bad, mkay?

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jan1320@reddit

I'd say carbon buildup could potentially be a concern in the long term

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ProfessionalKick8487@reddit

@ eatsbagelsdaily. List your certs and how many motors you Java rebuilt in your lifetime?

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christian_l33@reddit

Tell me you're American without telling me...

In short, yes, you are creating a situation that will shorten the life of your engine. How short? Depends on your maintenance regimen and luck.

Basically, idle is one of the worst times for fuel combustion efficiency. This creates wear on O2 sensors, carbon build up, clogging of your catalytic converter.

Also, you are creating excessive heat without ambient wind flow around your engine. As your engine becomes heat soaked, the cooling system cycles off/on constantly, putting excessive heat on all your components under the hood. All this extra heat is prematurely shortening the life span of random engine components. (Alternator, water pump, valves and gaskets, ect...)

it CAN be potentially life threatening.

if you have a small leak in the exhaust pipe, it will not be a problem if the car is moving and fresh air is coming in.

if there is an exhaust leak, or if someone did some work to the back hatch/trunk and did not re-install the plastic air dam, then exhaust gas can in fact enter the car. then you go for the big sleep

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spoopyboobies@reddit

If the battery is healthy it should be fine. Worst case scenario you need a jump because your battery dies

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Kdoesntcare@reddit

The car will be fine but mother nature is watching you with tears in her eyes. 😐 /s

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Mike312@reddit

I would recommend against it.

You're wasting gas as others have made clear.

You're adding another heat cycle to your engines gaskets which will cause them to wear out sooner.

Because you're parked and not moving, air flow is limited so the heat soaks in the engine bay - this is worse in the summer. Some components, esp rubber ones, will wear out quicker from this heat.

Your fluids and other systems are still running, so you'll need to change a lot of those sooner (esp oil changes). Several people have said the 30mi/hr of idling rule, which might double your oil change frequency if your commutes are short; probably do 5k/6 mo if you're doing this regularly.

A few people have mentioned "cop cars do this all the time". Yes, they do, and if you've ever worked on one that's spent most of it's time like this, the rubber and plastic in the engine bay can be brittle AF and they run like shit, and PDs spend a ton of money and often have their own dedicated mechanics maintaining their fleet...do you?

Inner_Grab_7033@reddit

As long as your car doesnt have a Hemi or is generally not a truck with a large engine you'll be fine

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baldieforprez@reddit

Ok-Implement4608@reddit

It won't straight up wreck your car, but sitting at idle for 1 hour is rougher on your car than if you just drove for 1 hour.

You will burn plenty of gas and maybe some carbon buildup on DI engines, but it’s not the end of the world. Heck, I live in the northeast and if I want a warm cabin in the winter, I basically have to idle it for a few minutes in the morning to get any heat out of the vents.