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How Long Can A Semi Truck Idle? (12 Facts You Should Know!)

Have you ever wondered why semi-trucks are often idling their engines?

Perhaps you would like to know why truck drivers idle the engine and whether it really is necessary.

If you have a semi-truck of your own, there are some important things you need to know when it comes to idling a semi-truck.

Read on to find out more.

Here’s a quick answer to How Long can a Semi-Truck Idle:

Semi-truck engines can idle for long periods of time without using a lot of fuel. This can be to warm up the engine, prevent diesel gelling, or power appliances in a sleeper cabin. However, it is important to note that there are some laws against idling in some areas.

What does it Mean for your Semi Truck to Idle?

Idling is when the vehicle is stopped with the engine running. In the majority of cases, the driver will put the vehicle in neutral when idling.

However, a vehicle can also idle when it is in gear, only if the clutch pedal is engaged. If the clutch pedal is not pressed down the engine will stall.

Idling means that the engine will be running at its lowest possible revolutions per minute (RPM) without cutting out. In most cases this is between 1000 and 2000 RPM, however, it depends on the vehicle.

An idling vehicle will still use gas to keep the engine running. However, it will be using a minimal amount, since the engine is running at a very low speed (RPM).

Having the engine idling is not necessarily bad for the engine unless the temperatures are high. However, it can be bad for the environment since the engine is still burning fuel but is technically not in use.

Why Would You Need to Idle Your Semi Truck?

There are several reasons why you would need your semi-truck to idle.

Some of these are important and can help save you money, others are important to the health of the semi-truck engine.

The most common time when a semi-truck’s engine needs to idle is when it is stopped in traffic. Even if the traffic is moving slowly, it is better to let the engine idle than to turn it off.

Turning the engine off and back on over short periods of time will actually use more fuel than leaving it idle. This can include waiting at a red light or even sitting in traffic.

In colder weather, it is important to let a semi-truck’s engine idle after turning it on. Driving with a cold engine can cause some serious damage to your semi-truck.

Allowing the engine to idle will give it time to warm up and let the fuel and oil flow through the system. This allows the semi-truck to be driven safely in colder conditions.

Semi-trucks also use the engine to generate air pressure for their air brakes. Leaving the engine to idle helps this process to be more efficient and allows the brakes to be more effective.

Semi-trucks have a lot of amenities that use electricity. This is especially common in sleeper cabins where you can often find TVs or fridges.

Using these can drain the battery. However, if the semi-truck’s engine is idling, then the alternator can keep the battery going, allowing the driver to use their comforts without worrying about having a dead battery later on.

At what Temperature should I leave my Semi Truck Running?

A semi-truck should be kept running when the ambient temperature reaches below 15 degrees Fahrenheit or -9 degrees Celsius. Idling at these cold temperatures will prevent the gelling of diesel fuel from taking place, which may cause damage to the engine.

Colder temperatures mean that the engine needs to be warmed up before driving.

Extreme cold temperatures can cause many problems for your semi-truck. Although they are stronger and more durable than your average car’s engine.

This means that the semi-truck engine can withstand colder temperatures, however, to be safe, you should let your engine idle if the temperatures reach 15F/-9C outside.

Temperatures below freezing can also cause gelling to take place in your diesel. This will make the fuel unusable until it is warmed up.

You can use a weather app on your phone to get an hourly breakdown of the ambient temperatures in your region. 

Allow your semi-truck to idle for at least 5 minutes before driving. This will give it time to warm up and pump the fuel and oil through the entire system.

When you’re driving, it’s also a good idea to take it easy on the throttle for a least 20 minutes to ensure that the engine is properly warmed up.

What RPM should a Diesel Idle At?

On average, semi-truck diesel engines idle between 600 and 900 RPM. Some older diesel engines can idle at up to 1200 RPM. If the engine idles below 600 RPM, there is a serious risk of stalling, and with an idle above 1200 RPM, this could mean that too much fuel is getting to the engine.

Diesel engines should be idling between 600 and 1200 RPM depending on the manufacturer and the age of the engine.

If the revs drop below 600 RPM there is a serious risk of the engine stalling. It could indicate that the engine is too cold, or there is another problem that you need to take a closer look at.

If the engine is idling over 1200 RPM it will be using too much fuel and overheating the engine in the long term, which can lead to engine failure.

This could be indicative of an engine problem, and you should get it checked out and serviced as soon as you can.

How Long Can a Semi Truck Idle?

In the majority of cases, it depends on the brand and age of the semi-truck. Older semi-trucks may not be able to idle as long as newer semi-trucks.

Idling an engine can reduce the lifespan of the engine as it counts as running hours. However, since the engine is running at a low RPM, it does not do as much damage.

Newer semi-trucks are able to idle the engine at a lower RPM, which makes it less damaging to their engine’s lifespan.

Many truckers leave their semi-truck engines top idle all night long, others have automatic shutdown systems that will switch the engine off when it reaches a set temperature.

How Long Can a Semi Truck Idle on a Full Tank of Gas?

It is estimated that idling a semi-truck can use on average up to 0.8 gallons of fuel per hour. This amount will vary depending on how fuel efficient the semi-truck is.

Semi-truck fuel tanks can hold between 120 and 150 gallons of fuel, and some semi-trucks have two fuel tanks installed, which means they can hold up to 300 gallons of fuel.

This means that a semi-truck can idle for 187,5 hours on a 150-gallon tank of fuel. That is equal to just over 7 and a half days. 

If a semi-truck has two 150 gallon tanks, it can idle for double that amount of time in theory.

Is Idling a Semi Truck Bad?

Idling a semi-truck engine can shave time off its lifespan. It also means that maintenance needs to be done more frequently because it technically counts as running hours for the engine, though it will not be working as hard.

Idling a semi-truck’s engine for long periods of time means that it gets less rest in between driving. This can cause more damage and wear in the long term.

It also means that more regular maintenance is required for the engine.

Reports show that if a semi-truck engine idles for extended periods of time it can result in up to $4000 in extra maintenance costs.

Can you Leave a Diesel Running All Night?

You can leave a diesel engine running all night. In fact, it is a common sight at truck stops. You can often find multiple semi-trucks with their engines running all throughout the night.

However, if the ambient temperatures are too high, then it can cause problems for your semi-truck’s engine. 

Leaving the engine to idle all night will not give it a chance to rest and cool down. This means it can easily overheat throughout the night if the ambient temperatures remain high.

Idling the engine will cause its temperature to rise because there is no air flowing into the radiator, which is designed to cool the engine by catching oncoming wind while driving.

This overheating can lead to problems in the future and a shorter lifespan on your diesel engine.

Why do Truckers Leave their Trucks Running All Night?

In most cases, drivers will leave their semi-trucks running to regulate the temperature inside the cabin while they sleep.

The cabins of semi-trucks, especially the older ones, have poor insulation, which means that the cold or heat from the outside can be punishing, especially if you are trying to sleep after a long day.

Other reasons why truckers leave their engines running all night could be to keep their amenities running.

This can include TVs, fridges, and radios. Any of these can often be found in a sleeper cabin semi-truck. They also use a lot of electricity.

If they are left running with the engine off, they can quickly drain the battery of the semi-truck, which means that it won’t start the next day.

Keeping the engine running allows the alternator to charge the semi-truck’s battery while these appliances are being used.

In colder temperatures, diesel can also ‘gel’. Gelling is when the fuel reaches below freezing and turns into a waxy, gel-like substance, making it unusable until it is warmed up.

Is it Bad to Let a Diesel Idle for Hours?

Idling a semi-truck’s engine for long periods of time won’t cause major damage to it, so it’s not necessarily bad. 

However, it can shave some life off the overall lifespan of the engine since the idling counts as running hours. This means that more frequent repairs and maintenance may be needed.

It is only bad to keep a diesel idling for hours if the ambient temperatures are extremely high. This will cause the engine to overheat quickly.

Semi-truck engines have radiators that catch the oncoming wind while the truck is moving, this helps to keep the engine cool. If the semi-truck is not moving, there is no wind to keep the engine cool while it is running.

In some cases, though a semi-truck engine will need to idle for long periods of time. If a driver is at a truck stop and the outside temperatures are extremely cold, idling the engine can prevent the fuel from gelling. 

It will also allow the driver to remain warm inside their cabin as most semi-trucks have poor insulation and need the cabin temperature to be regulated.

How Much Fuel does a Semi Truck Burn while Idling?

Semi-trucks burn around 0.8 gallons of fuel per hour while idling. This may sound like a small amount, however, over longer periods of time it can add up.

Even when diesel costs as little as $2.50 a gallon, fuel for one 10-hour rest period will cost $20. If a rest is needed every day, it can cost up to $140 per week.

Over the course of a year, this can cost you around $7300 if your semi-truck drives every day and idles for 10 hours per day.

What are the Semi Truck Idling Laws?

There are many states in the U.S. that have clamped down on the laws around idling semi-trucks. The primary reason is to reduce smoke emissions and it’s impact to the environment thereof. Punishments such as large fines can be given out if any of these rules are breached.

Popular Places in the U.S. and their Idling Laws:


Prohibits the emission of “visible air contaminants from diesel-powered motor vehicles or other movable sources” of a shade or density greater than 20% opacity for longer than five consecutive seconds.


Regulates smoke emissions and limits idling to five minutes statewide. There are exemptions for traffic conditions, onboard equipment like reefer units, and for heat/cooling for drivers sleeping in parked vehicles.


Regulates smoke emissions statewide. Idling is limited to 30 minutes at marine ports and terminals processing 100,000+ containers per year.

Certain municipalities also limit idling. The California Air Resources Board has also announced that it is considering a statewide ban on the idling of heavy-duty diesel vehicles.

Beginning with the model year 2007, idling would be limited to five minutes and vehicles would be required to have a tamper-proof engine idle shutdown device or Alternative Power Unit (APU).


Regulates smoke emissions statewide. Idling restrictions are also in place within Denver, Aspen, and Colorado Springs. There are certain exemptions for low ambient temperatures, emergencies, etc., but not for sleeping in the vehicle.


Limits idling to three consecutive minutes. Certain exemptions are made for traffic congestion, breakdowns, engine heating at temperatures below 20 degrees F.

Exemptions can also be made for the operation of heating, cooling, or auxiliary equipment if necessary to accomplish the intended use of the vehicle.

Air Management personnel enforce the regulations.

District of Columbia:

Limits truck idling to three minutes, unless the vehicle is powering PTO or ambient temperature is below 32 degrees F.

Enforcement is handled by Air Quality Division field officers, metropolitan police, and parking enforcement personnel.

Fines are $500 for a first offense, $1000 for a second, $2000 for the third, and $4000 for a fourth offense. Other penalties may also apply.


Idling restrictions are in place for Atlanta.


Idling is prohibited statewide, including for powering A/C. There are some very limited exemptions.

The Department of Health enforces the regulations. Fines can reach $25,000 per day for each offense.


Idling is prohibited on business streets statewide for longer periods than is necessary to load/unload.


Idling is generally limited statewide to five minutes, with some specific exemptions. The State Highway Patrol enforces idling regulations.


Idling is limited statewide to five minutes with certain exceptions. Regulations may be enforced by police, fire, board of health, or building inspection personnel.

The City of Boston actively enforces anti-idling restrictions with a dedicated anti-pollution enforcement team.


The City of Owatonna limits idling on residential streets.


The City of St. Louis limits truck idling to ten minutes. There is a fine of up to $500 for violations and the possibility of up to 90 days imprisonment.


During periods of poor air quality as declared by the health department.

Lewis & Clark County limits idling to two hours in any 12-hour period. The City of Helena limits idling to two hours.


Regulates smoke emissions statewide and limits idling statewide to 15 minutes except for emergency vehicles, vehicles in traffic congestion, while vehicles are being repaired, for the operation of certain specified equipment, or when emissions are treated and/or contained by an approved means.

Fines are $100 to $500 for a first offense, $500-$1000 for a second, $1,000-$1,500 for the third and $1,500-$2,500 for a fourth offense.

New Hampshire:

Limits idling statewide to five minutes if the ambient temperature is above 32 degrees F. Limits are extended to 15 minutes when the ambient temperature is between –10 degrees and +32 degrees F.

Unlimited idling is permitted if the temperature is below –10 degrees F. “where no nuisance is created.”

New Jersey:

Limits idling of diesel- or gasoline-powered trucks statewide to three minutes unless the vehicle is at the operator’s place of business, then the limit is 30 minutes.

If a vehicle has been stopped for three or more consecutive hours, idling is limited to 15 consecutive minutes.

There are specific exemptions, including for operating refrigerator units and PTOs and for truck sleepers in non-residential areas if the driver is sleeping or resting.

New Mexico:

Regulates smoke emissions statewide, specifically including emissions during idling.

Smoke opacity is limited to 30% for no more than ten seconds at altitudes of less than 8,000 ft. or 40% when a vehicle is being started.

New York:

Limits diesel truck idling statewide to five minutes with exemptions for powering certain auxiliary equipment such as PTO’s or cranes or if a truck is motionless for more than two hours and the ambient temperature is below 25 degrees F.

Within New York City, idling is limited to three minutes. Anti-idling laws are enforced, generally by the State Highway Patrol.


Limits diesel truck idling within the City of Philadelphia to two minutes.

Trucks may idle for up to five minutes when the ambient temperature is below 32 degrees F. and for up to 20 minutes when the temperature is less than 20 degrees F.

Enforcement is by Air Management Services or police department personnel. Fines are $300 per day, per violation with court appearances possible for repeat offenders.

Rhode Island:

Regulates smoke emissions statewide.


Has local idling limits for diesel trucks in several cities, including Houston and Dallas.

In eight counties in the Houston-Galveston area idling is also prohibited for more than five minutes during the months of April through October.

There are some exemptions. Fines range from $500-$1,000.


Regulates smoke emissions statewide and limits continuous idling to 15 minutes in Salt Lake, Davis, and Utah Counties in the Salt Lake City area.

Davis and Utah Counties permit up to 45 minutes of idling in a 120-minute period. There are certain exemptions, including for emergency vehicles, to supply power to refrigeration units and to supply heat/AC to sleeper cabs.

In Salt Lake County, environmental, health, police, or Highway Patrol officers may issue citations.

Fines typically begin at $500 and are determined by the nature of the violation.


Limits idling to three minutes in commercial and residential areas unless it is to provide power for devices other than for heating or cooling the driver.

Diesel trucks may idle for up to ten minutes to minimize restart problems.

The Department of Environmental Quality enforces idling regulations.


Regulates smoke emissions statewide.

British Columbia:

Regulates smoke emissions province-wide.


Regulates smoke emissions province-wide.