A fuel tank is a valuable part of the internal combustion engine system of any vehicle, motorcycle, airplane, or generator. The main purpose of the tank is to carry and feed the engine with the fuel safely, but it also just sits full of liquid too. Inquiries of the "What is inside a fuel tank?" nature can answer beyond that gas, that diesel, containing many pre-integrated units with the sole use of being contained, to ensure safe containment as well as functional delivery of fuel.

In this article, we'll break down what a fuel tank contains, how it works, and why each part is crucial to engine performance and safety.

What Does a Fuel Tank Contain?

  1. Fuel (Gasoline, Diesel, or Alternative Fuels)

The principal materials of any fuel tank are naturally occurring fuel. This may be:

  • Gasoline (petrol)
  • Diesel
  • Ethanol blends (e.g., E10, E85)
  • Biodiesel
  • Compressed natural gas (CNG) or liquefied petroleum gas (LPG) in alternative systems

Depending on the engine design of the vehicle or equipment, the kind of fuel is used. Fuel tanks are made to provide leakage and corrosion protection, particularly for flammable material.

  1. Fuel Pump

Most recent cars have an electric fuel pump placed inside the fuel tank. The pump transfers the fuel from the tank to the engine via the fuel lines, at the correct pressure for efficient running of the engine. Older cars employ mechanically mounted pumps at the exterior of the tank.

  1. Fuel Sending Unit

All. That's it. That's your straightforward part of your fuel level. It contains a metal rod, a float, and a variable resistor. Whenever you change the quantity of fuel in your system of your fuel gauge, it would displace the float, changing resistance and giving feedback to your fuel gauge on your dash. It lets you know what amount of fuel is remaining within your tank.

  1. Pre-filter or Strainer (In Some Systems

Most newer vehicles have fuel filters on the outside, but some gas tanks have an installed pre-filter or strainer. These are used to filter out sediment or dirt before it reaches the fuel lines and clogs the injectors in the engine.

  1. Vent System / Charcoal Canister

The fuel tank is an isolated system to prevent vapor leakage, but it has to breathe. Pressure and vapors vent out instead of routing them to an evaporative emissions system (EVAP), which takes a suction through a charcoal canister. Vapors burn off in the engine rather than venting out to the atmosphere.

  1. Baffles (Inside the Tank)

Fuel tanks typically have baffles, which are barriers that assist in preventing the fuel from sloshing around considerably while turning or braking. This provides a smooth flow of fuel to the pump and stabilizes the vehicle and maintains its level.

  1. Tank Cap and Seal

The gas cap not only keeps fuel from escaping but also holds pressure and keeps the integrity of the fuel system in place. Newer caps also have pressure relief valves and safety locks.

Why It Matters

What's in a fuel tank is important for several reasons:

  • Safety of the vehicle: Working tank components minimize the risk of fire or vapor leakage.
  • Fuel economy: Proper operation of the fuel pump and a clean fuel filter will provide maximum fuel flow.
  • Maintenance: Identifying malfunction symptoms in the fuel system (i.e., low mileage or rough idling engine) could be a sign that the tank is not correct. 
  • Environmental influence: The new tanks and venting systems are made to reduce emissions of harmful pollutants.

A fuel tank is not merely a place to put fuel in—it's a system operating to store fuel in a safe manner, supply fuel, and manage vapor emissions. When selecting what to fill a fuel tank with, pay attention to something other than the fuel itself and turn towards the system, such as the pump, sensor, vents, and filters that all operate together to get your engine running efficiently and safely.