how long can a car run in a closed garage

[Marcus]

A car can run for a very short time in a closed garage before it becomes extremely dangerous—typically just 2 to 10 minutes. The primary risk is not from running out of oxygen but from a rapid, lethal buildup of carbon monoxide (CO), an odorless and colorless gas produced by the engine's exhaust.

The exact time depends heavily on the garage's size and the vehicle's engine. A large, modern garage with a small, fuel-efficient car might take slightly longer to reach dangerous CO levels than a small, airtight garage with a large truck. However, the risk is unacceptable in any scenario. Carbon monoxide binds to hemoglobin in your blood much more effectively than oxygen, preventing your body from getting the oxygen it needs, leading to unconsciousness and death swiftly.

Key Factors Influencing Buildup Time:

Factor	Impact on CO Buildup Time
Garage Volume (Cubic Feet)	A larger garage takes longer to fill with CO than a smaller one.
Engine Size & Type	Larger displacement engines and those running rich (burning more fuel) produce more exhaust.
Garage Ventilation	Even a slightly open window or vent can significantly slow the rate of CO accumulation.
Vehicle Age & Condition	Poorly tuned engines or faulty exhaust systems can produce higher levels of CO.
Idle RPM	A high idle speed will produce more exhaust gas faster than a low idle.

Never start a car in a closed garage, even if you plan to pull out immediately. Modern, well-sealed homes can allow CO to seep in from an attached garage, creating a hazard inside the house as well. The only safe practice is to open the main garage door completely before starting the engine and to pull the vehicle out into the open air immediately. If you need to warm up your car in winter, do so by driving it gently after starting, not by idling in an enclosed space.

[VanKing]

Let's be clear: you don't have time to wonder. We're talking a handful of minutes, max. That invisible carbon monoxide will knock you out before you even realize something's wrong. It's not like in the movies where you just feel sleepy. I treat every garage start like a drill: door all the way up first, then I turn the key. It's a non-negotiable habit, especially with kids around. Just open the door. Every single time.

[Rod]

From a mechanical standpoint, the question isn't about time but about parts per million (ppm) of CO. A car at idle can produce enough exhaust to raise CO concentrations to over 1,200 ppm in under two minutes in a standard two-car garage. At 1,700 ppm, you can experience headache and dizziness within an hour. At higher concentrations, effects are swift and severe.

• Primary Danger: CO inhalation, not oxygen deprivation.
• Critical Action: Always ensure full ventilation.
• Safe Practice: Start engine only with door fully open.

[VonBennett]

I knew a guy who thought he'd just "quickly" grab something from the trunk with the car running. The garage door was down. He passed out and was lucky his wife found him in time. He said he just felt a little lightheaded and then—nothing. Woke up in the hospital. It happens faster than your brain can process the danger. That story stuck with me. I don't care if it's raining or freezing; the garage door goes up before I even touch the keys. It's a silent killer.