How Long Can a Car Idle?

How long can a car idle? How long a car can idle would depend on some factors, including fuel tank size, running components, and fuel consumption speed.

Older cars idle for as long as 52 hours for a full tank of about 38 liters. Newer cars go less for about 12 hours, which is extremely dependent on the car model. Nevertheless, there are other factors that could contribute to how long a car can idle.

Since the engine is not motional, the vehicle is not performing thoroughly, except that the block warms up. The generated heat, especially in most modern cars, would be removed or reduced by the cooling system and replaced by block heat.

However, if the ambient temperature is cold, it replaces the displaced heat with the fuel burning. This process makes the engine consume more fuel per hour than it would in an open-air at 80F. So, we can mention that the motor design entirely determines how long a car can idle.

Is it bad to let your car idle for a long time?

Leaving your car idle is not entirely harmful, but it affects the car in some way. The first thing is that you waste gas, counting up to a gallon, within an hour, and it burns up oil. A car idling for a longer period may typically result in the circulation and burning up of more motor oil.

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How Long Can a Car Idle?

Let’s exclude hybrid and start/stop engines. The focus will also be on modern engines since most cars feature modern technology. Meanwhile, fuel consumption is between .35 and .45 per displacement liter per hour. Consider the following:

  • .54 liter per hour: .66 L/H – 1.5 liter engine
  • .72 liter per hour: 2.0-liter engine
  • 6 liter per hour: 4.6-liter engine
  • 91 liter per hour: 5.3-liter engine

Above is the minimum without additional running components like a fan, light, air conditioning, and park/neutral.

The rate of fuel consumption would also depend on the engine RPM (Revolutions Per Minute). Thus, since a bigger displacement engine is typically idle at a slower speed, they are towards the low end of gas consumption per displacement liter.

Tank size

A typical 2-liter engine taking a full tank of about 38 liters can idle up to 52 hours. A pickup truck with a full 100-liter and 5.3-liter engine will idle for 52 hours as well.

Diesel

Some engines consume faster because a typical diesel engine is not efficient, such that it burns more fuel to maintain a minimum vehicle load. Nonetheless, the fuel consumption number is quite close to the estimated consumption for fuel engines.

Minimal Load

In some cars, if the AC or some other loads are active, they affect the engine and engine running requirement. A small displacement engine such as a 1 Liter engine may go to high idle mode to save load, which may double gas consumption.

Computer Tech

Depending on the ECM (Engine Control Module), some loads, including the air conditioning, may be disabled when idling.

Valvetrain

The valvetrain in some cars can idle at low-speed; thus, optimizing fuel consumption.

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How Long Our 90s Car Idled

To discover how long most cars can idle, we decided to idle Michael Owen, our team member, 90s Ford. The vehicle has a 20+ gallon tank (below 23), 300 CU, and in. I-6 (port injection).

Our janitor is instructed to idle the 90s Ford parked behind the organization’s building on a Friday midnight. Yes, we had the security guards confirm that the vehicle is running by checking it regularly throughout the weekend.

On Monday morning, everyone returned to the business premise early enough because of this project, and guess what? Our 90s Ford is still idling. Now, that’s about 53 hours of idling a typical old vehicle. However, the gas ran out as Owen drives to a gas pump within the site.

Following the number of hours and gallons, our vehicle idling for 53 hours would consume .378 gallons per hour, which is believable.

Is car idling bad for the Engine?

Not necessarily, but yes, idling your car is bad for the engine, especially if done often. However, an idled vehicle does not combust fuel completely because the engine is not fully operational. So, it leaves mechanical residues that may damage the exhaust system or degrade some components over time.

How bad is it to let a car idle for too long?

You would run out of gas when you idle a car for too long, which is the first degree of how bad it is to idle a car for too long. As mentioned earlier, although car idling is not entirely bad for your car, it leaves some effects, including circulating and burning up more motor oil.

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The police, nonetheless, idle your vehicles often. The obvious reason is to take off instantly, and they do not pay for gas either. Some taxi operators idle their cars, but most taxis now pay for gas, meaning they do not leave their cars idle regularly.

How much gas does a car burn per hour while idling?

Suppose we have a 2-liter engine throttled to 25% of external air pressure and idling at 700 rpm. Typically, fuel consumption depends on air consumption. Let the amount of air depend on the following:

  • Engine Speed: 700 rpm (350 cycles/min for a 4-stroke)
  • Engine Displacement: 2 liter
  • Manifold Air Pressure: The engine throttling level
  • Volumetric Efficiency: Efficiency of air exchange

Assuming we have 100% volumetric efficiency, the engine runs at a standard 15C day (sea level), and the manifold air pressure is equivalent to the air density (throttled to idle).

Air Consumption:

  • Displacement
  • Cycles
  • Volumetric efficiency
  • Manifold air pressure

2 Liters = 0.002 m^3

Air Density = 1.225 kg/m^3 * 0.25

Result =

0.002 m^3 x 350/minute x 100% x 1.225 kg/m^3 x 0.25 = 0.214 kg/min

Total fuel consumption becomes 0.0143 kg/min or 1/15

Final Thoughts

There is no complete answer regarding how long a car can idle. As mentioned earlier, variables, including engine size and fuel capacity, would factor in the duration of an idling vehicle.

While considering how long your car would idle, you would want to consider the damage level extensive idling can cause.

If your car has oil gelling problems, extended idling is not ideal. Besides, longer idling hours reduce the mileage between oil changes. It depends on the car, though, but typically 25-35 miles per hour of idling before the next oil change.

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