Why Turning Off the Engine Matters

First things first: never pump gas with the engine on. Sure, the odds of a fire are slim, but why take that chance? Gas stations everywhere stress the importance of shutting off the engine and putting down the phone while filling up.

How Does a Car’s Fuel System Work?

Gasoline (or diesel) gets stored in a tank, usually tucked away near the back of the vehicle. Most tanks hold between 45 and 65 liters of fuel. Filling up is as simple as inserting the nozzle and letting it flow.

Once the fuel is in, a pump sends it through the lines to the engine. It passes through a filter to catch any debris that could mess things up. After that, it gets compressed and sprayed into the engine’s cylinders or intake, depending on the type of injection system. Older rides might still use carburetors instead of injectors.

In modern cars, the fuel pump runs on electricity. That whine heard when the ignition is turned on? That’s the pump kicking into gear. Older models might have mechanical pumps that create a vacuum to pull the fuel through.

What’s a Fuel’s Flashpoint?

Understanding a fuel’s flashpoint is key to grasping why running a car at a gas station can be risky. Gasoline and diesel are super flammable. Gasoline ignites at around 247°C (477°F) as a liquid, but its flashpoint—the temp at which it can catch fire as a vapor—is a chilling -43°C (-45°F). That means a tiny spark or a hot surface could ignite fuel vapors floating in the air. Thankfully, this is pretty rare, as it takes a specific concentration of gasoline in the air for combustion to happen.

Is It Dangerous to Fill Up with the Car On?

Pumping gas with the car running? Not a smart move. While the chances of something going wrong are tiny, it’s still possible. Gas stations might not make it illegal, but they sure do enforce the rule of turning off the engine.

The risk comes mainly from static electricity. It builds up when electrons move from one surface to another, creating an imbalance. This imbalance can spark and ignite fuel vapors. Plus, if spark plugs are faulty, they could potentially ignite those vapors too. Even though the concentration of fuel vapors at a station is usually too low to combust, it’s better to play it safe.

What Else Could Cause a Fire at a Gas Station?

Fires at gas stations can happen due to various reasons, and they’re often more likely than a car catching fire. Here are a few:

• Cigarettes and Flames: Smoking near fuel is a big no-no. A tiny ember can travel and ignite fuel vapors from a distance.
• Hot Car Parts: Components like the catalytic converter can heat up significantly and ignite nearby vapors, especially after a long drive.
• Sparks: Static electricity can build up in people too. Avoid touching metal objects or opening car doors while fueling to prevent sparks.
• Random Car Fires: While it’s rare, some cars can catch fire due to faulty wiring or overheating. Turning off the engine reduces this risk.

Why Leaving the Car Running is a Bad Idea

Even if the fire risk seems low, there are other reasons to keep the engine off while fueling:

• Safety Hazards: Kids or pets could accidentally shift the car into gear, causing accidents or damage.
• Pollution: Idling cars contribute to air pollution, and it’s illegal in many places to leave a vehicle running without cause.
• Theft Risk: Leaving the car running while stepping away for a moment can invite thieves. Insurance might not cover it if the keys are left inside.