What RPM Should I Idle My Semi Truck? Here’s the Answer

Truck idling is an unavoidable part of a truck driver's lifestyle. Truck drivers often spend up to 11 hours a day on the road, and a good portion of that time may be spent idling. There are also reasons that may call for a driver to idle their truck overnight, some of which are unavoidable.

Occasionally it is necessary to idle your truck. It's often recommended that you shouldn't idle the engine because it can harm the engine and the environment. However, in certain situations, it is the preferred option. In some circumstances, the driver's health and safety might even depend on it. The key to idling your engine safely in these situations is knowing the side effects of idling, and what rpm you can safely idle your semi-truck.

Why is Idling Not Recommended?

There are several reasons why idling your semi-truck is not recommended. While it may be necessary for some situations, it can also cause some level of harm to the environment and the truck engine.

• Wastes Fuel and Money

When you idle your truck, the engine keeps burning fuel. This might not seem like much if you're only idling for a few minutes in traffic, but it starts to add up over time. Idling for a few hours every day can lead to as much as thousands of dollars in fuel wastage over the course of a year.

• Harmful Emissions

Your truck engine produces harmful emissions while it idles. These emissions can find their way into the cabin. If the ventilation in the semi-truck cabin is insufficient, then this can lead to adverse health effects for the driver. If the vehicle is allowed to idle for prolonged periods in this condition, it can even lead to asphyxiation.

• Causes Unnecessary Wear on the Engine

Semi-trucks are much different from cars in many ways. They're designed to pull heavy loads for long periods. As a result, their engines are built for power. These powerful engines don't take well to idling, however. There are several ways idling can cause damage to your truck's engine.

• Wear and Engine Damage

If the engine is allowed to idle at low RPMs for too long, it can lead to wear on the cylinder walls, pistons, and gaskets. This is because of insufficient oil pressure which doesn't allow the engine oil to circulate fully throughout the engine. As a result, the cylinder heads at the top of the engine may not receive adequate lubrication, which produces wear in this region of the valvetrain.

• Overheating

When your truck is idling, the engine is generating heat, but there's no airflow into the engine. This results in the engine temperature rising. If the ambient temperature is high, this can cause the engine to overheat.

• Carbon Deposits

When idling, the engine typically operates at a low RPM and doesn't combust fuel completely. After idling for extended periods, this results in carbon deposits in the valves and exhaust system. These carbon deposits build up and can cause engine inefficiency, and even damage.

• Increased Maintenance Costs

When the engine is left to idle too often, it means that the engine has less time to rest. This results in longer operating time and puts extra strain on the engine, which results in more frequent engine troubles. This in turn leads to higher maintenance costs.

How Can You Idle the Engine Safely?

Perhaps you still need to idle your engine anyway. Many reasons might call for you to let the engine run idle.

• To run the AC or heater in severe temperatures. If the weather is too hot or too cold, you might need to turn on the air conditioning or heater to keep the temperature at a safe level.
• To keep the engine and fuel warm in cold weather. Many truck drivers have experienced the dreaded situation where their engine is too cold to start in the morning. Most trucks use diesel fuel which requires higher temperatures to combust. This makes truck engines more vulnerable to hard starting in cold weather.
• To run electronic appliances inside the truck without draining the battery.
• When the truck is stuck in stop-and-go traffic, and you don't want to stop the engine too frequently.

Whatever your reason might be for needing to idle your truck, there are some precautions that you can take to idle safely while keeping emissions and engine damage to a minimum.

• Check for Exhaust Leaks

This is one of the most important things you should look out for in your vehicle. Checking for exhaust leaks should be part of your maintenance checklist. Exhaust leaks are dangerous while you're driving, but they are even more dangerous while you're idling. This is because the truck is not moving, so fumes can build up in and around your vehicle while you're idling.

Exhaust leaks can allow harmful toxic fumes into the cabin, where they will negatively affect your health. They can increase your cancer risk or cause asphyxiation. They can also cause engine damage. If you locate an exhaust leak, it should be fixed promptly.

• Roll the Windows Down

If the weather conditions aren't too harsh, you should roll the windows down. This will allow fresh air into the vehicle and prevent exhaust fumes from building up inside the cab.

• Keep a Carbon Monoxide Detector

For the sake of safety, it is important to keep a carbon monoxide detector in the truck. Truck drivers are at risk for carbon monoxide poisoning because of their exposure to truck exhaust fumes. Trucks produce more carbon monoxide than cars.

When idling overnight or for long periods, a carbon monoxide detector will warn you if the exhaust fumes are making their way into the cab and building to unsafe levels.

• Idle Your Truck at an Appropriate RPM

Idling your truck at the right RPM is important to minimize the effects of idling on the engine. Idling at the right speed minimizes fuel wastage and ensures proper oil flow through the engine. It also ensures the complete combustion of fuel, which prevents the undesirable effects of incomplete combustion, such as:

• Diesel slobber
• Rough Idling
• Carbon deposits in the exhaust system

Idling too high wastes fuel and causes extra wear on the engine. It can also result in overheating and engine damage. Idling too low results in incomplete combustion of the fuel. It also fails to raise the oil pressure to suitable levels, leading to oil starvation in certain parts of the engine.

Idling at the wrong RPM will shorten the life span of your engine. Of course, you want to preserve your truck's lifespan, while still being able to idle when the need arises. This leads to the question, "What RPM should I idle my semi-truck?"

What RPM Should You Idle Your Semi Truck?

Idling the engine at the right RPM is very important. If the RPM is too low, then the oil pressure won't be sufficient to deliver oil to the cylinders at the top of the engine. If the RPM is too high, then the engine will waste fuel and runs the risk of overheating in hot weather.

Finding the right RPM is very important for minimizing engine damage. Generally, it is recommended to idle your truck at 900-1500 rpm. However, the best idle RPM varies from vehicle to vehicle. Idling at 900-1500 RPM will work for most semi-trucks, but you can try the following steps to find the best RPM for your vehicle.

1) Oil Pressure

Watch the oil pressure. Once you start to press down on the acceleration and raise the RPM, you should notice your oil pressure gauge rising. Continue to press down on the acceleration and take note of the RPM that gives you optimal oil pressure. Sufficient oil pressure is needed to make sure the entire engine is well-lubricated. If you idle your semi-truck's engine with low oil pressure you run the risk of damaging the valve train and fuel injectors.

2) Smooth Idle

While idling your semi-truck, make sure to feel and listen for the point where your idle begins to smooth out.  A smooth idle indicates that complete combustion is taking place in the cylinders. This minimizes the production of harmful emissions and prevents the formation of carbon deposits in the cylinders. It also prevents diesel slobbering.

If you keep an eye out for these two conditions, you should be able to find an idle RPM where you have sufficient oil pressure and a smooth idle. This is the idle RPM that works best for your particular vehicle.

Conclusion

While it is generally recommended that you shouldn't idle your semi-truck, there are some situations where it is the only viable decision. Knowing how the RPM to safely idle your truck will help you keep engine damage, fuel wastage, and emissions as low as possible.

Idling at 900-1500 RPM is usually the best solution. The appropriate RPM differs depending on the vehicle, but you should use an RPM that provides good oil pressure and a smooth idle. This is so that the engine oil will circulate to reach the top cylinder heads in the engine and keep them well lubricated.