Fuel Tank Pressure: Potential Causes And Solutions

Pressure in a fuel tank is a normal occurrence, but excessive pressure can be dangerous. The pressure in a fuel tank is caused by the vaporization of gasoline, which is made up of over 500 different hydrocarbons. This vaporization is accelerated by heat, so the temperature of the gasoline is a key factor in the amount of pressure in the tank. The pressure can also be affected by the EVAP system, which stabilizes pressure in the fuel tank. If the EVAP system fails, becomes clogged, or is restricted, it can lead to a dangerous increase in pressure.

A faulty EVAP system

However, if the EVAP system is not working correctly, it can cause pressure to build up in the fuel tank. This can happen if the system becomes clogged, restricted, or fails altogether. For example, the charcoal canister can become clogged with excess buildup over time, preventing gas fumes from entering or exiting the canister and causing pressure to build up in the tank. Another possible issue is a stuck-open purge valve, which creates a vacuum leak that affects the engine by allowing too much air to enter.

Additionally, a kinked fuel vapor line or a failure in the purge control or vent solenoid can prevent the vapor pressure in the tank from moving through the EVAP system, leading to increased pressure in the gas tank. It's important to note that while a small amount of pressure in the fuel tank is normal, excessive pressure can lead to hazardous situations, including the risk of fire. Therefore, it's crucial to address any issues with the EVAP system promptly to ensure the safety and proper functioning of your vehicle.

Blocked vent line

A blocked vent line can cause pressure to build up in your fuel tank. This is because the vent relieves pressure and vacuum, which is necessary as fuel is in a constant state of expansion and contraction as it warms up and cools down.

A blocked vent line can be caused by a sag or belly in the hose, which causes fuel to become trapped in the line. This can prevent the tank from venting and also starve the engine of fuel. It can also be caused by a blocked screen on the fuel vent, which can become clogged with corrosion, salt crystals, and grime over time.

To check if your vent line is blocked, you can shoot air into the air vent line using a compressor. If the vent is blocked, it will result in no sound. You can also try blowing through the canister vent line that has been disconnected from the gas tank.

To fix a blocked vent line, you can try using compressed air to blow out any blockages. You can also try putting wire or plastic tubing through the vent to clear any blockages. If the blockage is caused by a sag in the hose, you can try to straighten the hose to prevent fuel from becoming trapped. If the blockage is caused by a clogged screen, you can clean it with a small wire brush or replace the vent if the mesh is corroded.

It is important to address a blocked vent line as it can cause pressure to build up in your fuel tank, leading to potential damage.

Gasoline vaporisation

Vapor lock is a problem caused by liquid fuel turning into vapour while still in the fuel delivery system. This disrupts the fuel pump and causes a loss of pressure to the carburetor or fuel injection system, resulting in a loss of power or engine stalling. This can be caused by the fuel being heated by the engine, the local climate, or a lower boiling point at high altitudes. Older fuel systems were more prone to vapor lock, as they used low-pressure mechanical fuel pumps driven by the engine and located in the engine compartment. Modern engines have fuel injection systems and electric submersible fuel pumps inside the fuel tank, which helps prevent vapor lock.

The amount of pressure in the gas tank depends on the temperature of the gasoline. Higher temperatures mean more pressure. This pressure can be released by carefully pushing the valve inside the fitting using a rag and a screwdriver, or by simply unscrewing the gas cap when filling up.

To prevent gasoline vapours from escaping, car fuel tanks are pressurised. This helps to control and capture the vapours, reducing the amount that can escape and contributing to environmental protection. The EVAP system in cars filters the fuel vapours and prevents the gas tank from becoming overly pressurised, which could result in hazardous situations such as fires.

Heat

The amount of gas released by the liquid is directly proportional to its temperature. This is usually stabilised by the evaporative emission control system, or the EVAP system. However, if this system fails, or becomes clogged or restricted, it can result in a pressure build-up.

The EVAP system contains a charcoal canister to absorb excess gas from the fuel system. Over time, this canister can become clogged, preventing gas fumes from entering or exiting. This will cause a pressure build-up within the tank.

Another cause of pressure build-up due to the EVAP system is when the purge valve is stuck open, creating a vacuum leak that affects the engine. A large quantity of air will enter the engine, resulting in a change in the car's air-to-fuel ratio.

Additionally, a kinked fuel vapour line or a failure in the purge control or vent solenoid can also lead to increased pressure. These issues prevent the vapour pressure in the tank from moving through the EVAP system, causing a rise in pressure in the gas tank.

It is important to note that while heat significantly affects fuel tank pressure, it is unlikely to cause an explosion. Gasoline has a high auto-ignition temperature of 536 °F (280 °C), and the maximum temperature reached inside a running engine on a hot day is typically around 270 °F (130 °C). Therefore, the fuel in the tank will not spontaneously ignite due to heat.

A stuck fuel injector

There are several ways to identify a stuck fuel injector. One method is to check the resistance of each injector using a multimeter. If the reading is over 20 ohms, the injector may be clogged. Another way is to pull the fuel rail and pressurize the system while observing the injectors for leaks. A third option is to monitor fuel pressure after shutting down the engine. If the pressure drops quickly and does not maintain for at least 15 minutes, it could indicate a leaking injector. Additionally, you can pull the spark plugs and observe if a particular cylinder is drenched in fuel, indicating a stuck injector.

To resolve the issue of a stuck fuel injector, you may need to replace the injector or perform a cycle through an ultrasonic cleaning process. It is also recommended to use high-quality fuel and regularly change the fuel filters to prevent debris from entering the fuel system and causing further damage.

Frequently asked questions