is it bad to sit in car with engine on

[LeHadley]

Yes, sitting in a car with the engine on for extended periods is generally a bad idea. The primary risks involve health hazards from exhaust fumes, unnecessary fuel consumption and emissions, and potential engine wear. While brief idling is harmless, prolonged idling—especially in an enclosed space like a garage—can be dangerous due to the buildup of carbon monoxide (CO), an odorless and deadly gas.

The negative impacts can be broken down into three main categories:

Health and Safety Risks The most critical danger is carbon monoxide poisoning. Modern cars are well-sealed, but if the exhaust system has a leak or you're idling in an enclosed space, CO can enter the cabin. Symptoms range from headaches and dizziness to loss of consciousness and death. It's a silent threat that demands respect.

Environmental and Financial Costs Idling is essentially getting 0 miles per gallon. You're burning fuel without going anywhere, which wastes money and unnecessarily releases greenhouse gases and other pollutants. The cumulative effect of millions of cars idling contributes significantly to urban air pollution.

Vehicle Wear and Tear Contrary to the old myth, modern engines do not need long idling periods to warm up. In fact, idling causes the engine to operate at a low temperature, which can lead to fuel dilution—where unburned gasoline seeps past the piston rings and contaminates the engine oil. This reduces the oil's lubricating properties and can increase long-term wear.

Aspect	Impact of Prolonged Idling (Approx. 1 Hour)	Supporting Data
Fuel Consumption	Wastes a significant amount of fuel.	A typical car burns 0.1 to 0.5 gallons of fuel per hour while idling.
CO2 Emissions	Contributes to greenhouse gases.	Releases approximately 1-2 pounds of CO2 per hour.
Cost	Direct financial loss.	At $3.50/gallon, idling costs $0.35 to $1.75 per hour.
Engine Wear	Can lead to long-term damage.	Fuel dilution can reduce oil viscosity by up to 30% over time.
Air Pollution	Releases harmful pollutants.	Emits nitrogen oxides (NOx) and particulate matter (PM).

For your safety and your vehicle's health, it's best to limit idling. If you need to run the car for climate control, ensure you are in a well-ventilated, open area and never in a closed garage. For warming up the engine, 30 seconds is all that's needed before driving gently.

[FelixMarie]

Honestly, it's mostly about the fumes and the waste. If you're parked in an open area for a few minutes, it's fine. But doing it for a long time, especially in a garage, is asking for trouble because of carbon monoxide. It's also just burning money for no reason. I turn the engine off if I'm going to be stopped for more than a minute. Saves gas and keeps the air cleaner.

[EstherLynn]

I think about it in terms of cost and common sense. My car's computer shows the instant fuel economy, and when I'm idling, it says 0 MPG. That's a clear sign I'm getting nothing for my gas money. Plus, I've read that it's not even good for the engine—it's better to just start driving gently after a brief warm-up. So now, if I'm waiting to pick someone up, I just shut it off. It’s a simple habit that saves a few bucks and feels less wasteful.

[StevenDella]

My main concern is always safety first. I remember a news story about a family who succumbed to carbon monoxide poisoning while sitting in a running car inside their attached garage. The gas seeped into the house. It's a tragic but real risk. Beyond that, idling your car in a neighborhood contributes to local air pollution, which isn't fair to your neighbors, especially kids with asthma. For me, it’s a no-brainer to avoid unnecessary idling. The potential consequences are just too severe.

[LeAdriel]

From a mechanical standpoint, modern engines are designed to handle short idling, but prolonged operation at low RPMs isn't ideal. It can cause incomplete combustion, leading to carbon buildup on intake valves and spark plugs over time. This "carbon fouling" can eventually cause rough idling and reduced performance. The engine also warms up much more slowly at idle than under light load, which can increase wear. So, for the longevity of your vehicle, it's better to drive off after about 30 seconds rather than letting it sit and run for extended periods.