Reasons for High Fuel Tank Pressure at Gas Stations?

[JamesFitz]

When driving, the temperature of gasoline also rises, causing slight volatilization. This results in the formation of gasoline vapor inside the fuel tank, leading to increased pressure. However, a charcoal canister is connected at the top of the fuel tank, designed to absorb these gasoline vapors. When pressure builds up, the vapors are absorbed by the charcoal canister, which then releases the pressure. Under specific operating conditions, these vapors are drawn into the engine cylinders and burned. Therefore, a certain level of pressure inside the fuel tank is normal, though generally not excessive, as the fuel tank is a sealed container and gasoline volatilization is limited. The hissing sound when opening the fuel tank cap doesn't necessarily indicate high pressure; it could also suggest low pressure. If the pressure is indeed high, it's essential to have it checked at a specialized 4S shop. Additional Information: 1. Introduction: Fuel additives, commonly known as "fuel enhancers" or gasoline additives, are complex chemical formulations. 2. Function: These products aim to improve combustion efficiency, reduce fuel consumption, enhance power output, clean carbon deposits, and lower emissions. In practice, their primary use is for carbon deposit removal, where they can eliminate minor carbon buildup and slow down the formation of new deposits.

[StLondyn]

The other day when I went to refuel my car, as soon as I opened the fuel tank cap, I heard a hissing sound with noticeable pressure. Later, I asked my mechanic friend about it, and he said this situation is quite common. The main reason could be that the activated carbon canister in the fuel tank is clogged. It's used to filter gasoline vapors, but over time, it gets blocked by dust, preventing the gas in the tank from escaping. Also, the vent valve at the fuel filler neck is prone to malfunction. If the spring is loose or the rubber seal is aged, the tight seal can easily trap gas. Additionally, this is especially noticeable after the car is exposed to the summer sun, as gasoline evaporates quickly, causing the pressure in the fuel tank to rise rapidly. Last time, I replaced the carbon canister, and now refueling goes smoothly every time.

[OAmy]

I often encounter cars with high fuel tank pressure at the auto repair shop and have summarized a few patterns. The fuel tank design inherently requires balancing internal and external air pressure; if the ventilation system fails, pressure builds up. The most common issue is a saturated and failed charcoal canister—that component near the vehicle's underbody gets clogged when filled with gasoline vapors. Another cause is a stuck pressure relief valve in the fuel cap; when unscrewed, gas can spray out. An overly thick sealing gasket on the fuel cap can also lead to this problem—I've seen several cars where the cap couldn't be unscrewed due to this. Additionally, refueling on hot days requires caution, as the pressure inside the tank can rise to twice the usual level, making early morning refueling safer.

[VonKevin]

Last time when I was refueling and encountered high pressure, I casually asked the gas station attendant. He said the main issue was with the fuel tank's venting system. Gasoline tends to evaporate into vapor, and under normal circumstances, these vapors are filtered through the charcoal canister before being released. However, many cars' charcoal canisters get clogged after seven or eight years of use, preventing the vapors from escaping. Another possibility is a design flaw in the fuel cap; some new cars have caps that are too tight, causing slow pressure release. Additionally, frequently filling the tank to the brim reduces the available space in the tank, making gas compression more noticeable. That day, he also reminded me that for older models, switching to an improved fuel cap can help alleviate the issue.