How Do Dual Fuel Tanks Work on Semi Trucks? Detailed Guide for Beginners in 2024

A semi-truck carries a heavy load. According to US jurisdiction, a semi-truck can load up to 80000 pounds. Likewise, the fuel tank of a semi-truck is far more complex.

It is, therefore, important to know how dual or multiple fuel tanks work in a semi-truck for proper maintenance. Proper maintenance can save thousands of dollars in long run.

Why Do Semi-trucks have Dual or Multiple Tanks?

Why Do Semi-trucks have Dual or Multiple Tanks

There are essentially two reasons behind dual or multiple tanks:

  • To get more fuel in the engine. Semi-truck travel long-distance carrying a heavy load on the back, so it can be difficult to stop and fuel up constantly. Having two or more tanks gives a long road without having to get fueled up.
  • Two or more are necessary to keep the truck balanced on the road and to prevent any risk factor. When filling fuel, modern trucks have an automatic balance to prevent one from being filled before the other one.

What Is inside a Semi-truck Fuel Tanks?

What Is inside a Semi-truck Fuel Tanks

Typically, fuel tanks are made of polypropylene, regrind plastic, high-density polyethylene, ethyl vinyl alcohol, or, a plastic adhesive. Fuel tanks can also be made of steel, iron, aluminum, and other materials that have high heat resistance.

Inside the fuel tank has a small low-pressure pump that mainly pushes fuel to the exterior pump. These pumps are important to keep the weight balance of the truck.

We should regularly do maintenance of the exterior pump as sludge builds up over time. Cleaning sludge is important to keep the effective and efficient movement of fuel.

How Much Fuel Does a Semi-truck Fuel Tank Hold?

How Much Fuel Does a Semi-truck Fuel Tank Hold

Well, it depends on lots of factors like the engine, the size of the truck, and the manufacturer of it.

On average, one fuel tank holds 120 to 150 gallons of fuel which means on average 300 gallons of fuel for one truck. To put that in perspective, you can approximately travel 2000 miles with it.

However, the driver should fill up to 95% of the total capacity whether that be 120 or 150 gallons. There are 2 important reasons behind this:

  • Risk of spilling: If you don’t leave any space for air in the tanks, it could spill out diesel fuel via overflow valves. It is not just bad for the environment, It might as well cause an unavoidable dangerous situation.
  • Fuel Expansion: Due to changes in temperature all matters either expands or shrinks. Fuel expansion works in the same principle. Thus, it can ever make minor changes to the weight of the fuel in tanks.

It is recommended not to let fuel tanks go down below 25%. (critical components of the system are not designed to operate on low fuel. You may cause immediate damage if you use the truck without fuel). You can check our guide How to adjust generator carburetor to reduce fuel consumption?

How Do Dual Fuel Tanks Work on Semi Trucks?

How Do Fuel Tanks Work on Semi-Trucks

In this part of the article we will discuss our main concern How Do Fuel Tanks Work On Semi-Trucks:

In semi-trucks, the tanks have usually located on both sides of the truck to keep the balance of the truck. In the dual fuel tank system, the fuel supply piping is arranged alternately to draw fuel from one tank or the other.

Another method( as the different companies use different methods depending on their model and price range) is a fuel transfer pump that essentially moves fuel from the auxiliary tank to the main tank. Then, the system takes fuel from the main tank and burns it makes energy.

Depending on the manufacturer or model and the age of the truck, the fuel transfer mechanism may be automatic or manually activated.

There are generally individual filler pipes. But modern designs may include multiple filler pipes from one central filler location to each of the tanks. There is generally a fill limit which restricts overflowing of fuel when refueling fuel in the tank

There is an emission control system (employed to limit the discharge of noxious gases from the internal-combustion engine and other components.) in every system which connects through a path with the dual system. The purpose of it is to collect, store and evaporate carbons from fuel. You also check our guide for How to Prime a Fuel Injected Engine?

Do You Need to Switch between Tanks?

Do You Need to Switch between Tanks

Modern semi trucks smoothly from one tank to another automatically. Old models of Semi-trucks do need manual input to switch.

You can typically switch between systems while you are driving trucks, but be cautious cause in rare cases, air buildup can cause the engine to sputter a bit. Check out the How does a high-pressure fuel pump work?

Does a Truck with 2 Gas Tanks have 2 Fuel Pumps?

Does a Truck with 2 Gas Tanks have 2 Fuel Pumps

In most gas pumps, each tank is associated with its own pump which enables safety if you choose to switch pumps while driving

If you feel like the truck is a little bit off pressure, you should check the both of the pumps and figure out the problem to save thousands of dollars

The fuel filter might be the cause so be sure to give it a look. Don’t forget to check the Aluminum Brazing Rods.

What Are The Problems That Often Occur in Dual-fuel Tanks?

What Are The Problems That Often Occur in Dual-fuel Tanks

It is a very subjective question and the answer depends on the age of the truck, manufacturer of the truck, and maintenance of the truck. But typically there are a few issues we often hear from dual-fuel tanks drivers:

  • Fuel Spill: Semi-truck fuel spill due to volume of the fuel tanks get. You need to be careful to look for it cause fuel is a flammable compound.
  • Inaccurate fuel reading: It is another known issue that can result in damage to your engine.
  • Overheating: Tanks can be overheating as a result of bad pumps and lack of fuel getting to the engine.


1. Are Dual Fuel Tanks Connected?

Some are, some aren’t. Often they are connected. It all depends on the application and personal requirements of the vehicle owner.

2. Does shooting at the fuel tank lead to a truck exploding?

Unless there is a spark or naked flames come in contact with the fuel, nothing happens. The fuel makes a hole in the tank and fuel will flowout. The friction between fuel and bullet won’t create enough heat to ignite to explode.


It is important to keep in mind that semi-trucks dual tanks technology is quite different from others. Hence, in this article, we have gone through explicit details to show you how it works.

Knowing How Do Dual Fuel Tanks Work on Semi-trucks not only just helps you to do maintenance work but also gives you a clear idea what are the things you have to keep in mind for the longevity of your truck.