why is my car still running after i turn it off

[StAutumn]

Your car continues running after you turn it off due to a phenomenon known as diesel engine runaway. This occurs almost exclusively in diesel vehicles and is caused by the engine unintentionally drawing fuel from a source other than the fuel injectors. Since diesel engines ignite fuel through compression heat alone, they don't require spark plugs to run. If an external fuel source enters the combustion chambers, the engine will keep running uncontrollably until that fuel supply is cut off or the engine destroys itself.

The most common culprit is engine oil being sucked into the intake system. This can happen due to a faulty turbocharger seal. The turbocharger is lubricated by engine oil; if its internal seals fail, oil can leak into the intake air path and be fed directly into the engine, acting as fuel. Another potential source is an excessively high level of engine oil, or "crankcase vapors" from a clogged Positive Crankcase Ventilation (PCV) system, which can overwhelm the intake with oil mist.

This is a serious and dangerous situation. The engine will rev to its maximum RPM, far beyond the redline, leading to catastrophic damage like seized pistons or connecting rod failure. Your immediate priority is safety. Do not try to restart the engine. If you're in a safe location, you can try to stall the engine by firmly applying the brakes while in a high gear (manual transmission) or by blocking the air intake with a rag or board—but this is a last resort and can be hazardous. The safest course is to evacuate the vehicle and call for professional help.

For gasoline engines, a similar but less severe issue is called "dieseling" or after-run. This is when the engine sputters for a few seconds after the key is off, often due to carbon deposits creating hot spots that ignite residual fuel. This is common in older cars but is typically not destructive.

Common Cause	How It Happens	Typical Engine Type	Severity	Immediate Action
Turbocharger Seal Failure	Engine oil leaks into intake	Diesel	Extreme (Runaway)	Attempt to stall engine or evacuate
Overfilled Engine Oil	Excess oil enters combustion	Diesel	Extreme (Runaway)	Attempt to stall engine or evacuate
Faulty PCV System	Oil vapors flood intake	Diesel	Extreme (Runaway)	Attempt to stall engine or evacuate
Carbon Deposits (Dieseling)	Hot spots ignite fuel	Gasoline	Low (Annoyance)	Usually harmless, needs tune-up
Faulty Idle Stop/Start System	System malfunction	Modern Gasoline	Low (Malfunction)	Cycle ignition, consult dealer

[LeWillow]

That’s scary, and it’s probably diesel runaway. It happened to my old truck once. The engine just wouldn't quit, revving super high. It turned out the turbo was shot and leaking oil into the engine, which it then burned like fuel. Don't panic. If you're safe, try to stall it by standing on the brakes in gear. If that doesn't work fast, get away from the car. It can blow up. This is a job for a tow truck and a mechanic, not something you can fix yourself.

[OLena]

This is a critical safety issue, particularly for diesel vehicles. The engine is drawing an unintended fuel source, most likely engine oil, and will not stop until that fuel is exhausted or the engine fails mechanically. Your safety is paramount. Do not attempt to restart the vehicle. If you are in traffic or an unsafe location, prioritize moving to a safe area away from the vehicle. The intense, uncontrolled operation can lead to fire or explosion. Contact a professional automotive service for immediate assistance. This is not a minor fault.

[LeviAnn]

Ah, the old run-on. On my '78 Olds, it would "diesel" for a second because of carbon buildup. But what you're describing sounds more serious—a true runaway. That's a diesel engine problem. It's feeding on its own oil, often from a blown turbo seal. There's no easy fix on the spot. The old-timer method is to shove a board over the air intake to choke it out, but that's risky if you don't know what you're doing. Better to just let the professionals handle it. That engine is living on borrowed time until it's stopped.

[Linda]

Okay, so the key is off but the engine is still going. First, is it a diesel? If yes, this is a known issue called runaway. The engine is burning a fluid it shouldn't be, like oil. It's a major problem. If it's a gas engine, it might just be 'dieseling'—a brief sputter from carbon deposits, which is mostly harmless. But for a diesel, the RPMs will climb dangerously high. The goal is to cut off its air supply. Look up where your air intake is; in an emergency, blocking it completely is the only way to stop it without catastrophic damage.