Owners Tips

5 Things You Didn’t Know About Gassing Up

Unless your car is all-electric, you’re making regular stops at the gas station. It all seems pretty straightforward, but there can be more to it than just pumping in the fuel. Here are five things you might not know about gassing up your vehicle.

Don’t Overfill the Tank

Auto manufacturers recommend that when the pump shuts off, you shouldn’t keep adding extra fuel to the tank. If you do, it could potentially get into the emissions control system.

Pollutants don’t just go out the tailpipe. Automakers also have to control fuel fumes, too. Excess fumes from the fuel tank are captured by a charcoal canister, where they’re stored and then later sent to the engine to be burned. If you overfill the tank by topping up, liquid fuel can end up in the canister, which can damage it.

The fuel cap is usually printed with a reminder to turn it until it clicks. The fuel system is a sealed unit and if you don’t click the cap – which completely closes and seals it – the system remains open. This can trigger a “Check Engine” light, which usually goes away once you’ve closed the cap and then driven a few kilometres.

Fuel Grade Matters

The numbers on the grades – 87, 89, 91, and sometimes 93 or 94 – indicate the fuel’s octane rating. Octane is a molecule and it’s not an additive that the refiners dump in. Rather, how the fuel is refined determines how much octane is in it.

The higher the octane level, the less volatile the fuel becomes. That’s important because when gasoline vapour is ignited in the engine, it ideally creates a flame front that moves smoothly throughout the combustion chamber for maximum efficiency. But high-compression engines can generate enough heat in the chamber that the fuel may spontaneously ignite before the spark plug fires, or create several flame pinpoints. The sound this makes is called engine knock or pinging.

On older cars, this could potentially damage the engine. Newer vehicles have knock sensors, and if it’s detected, the system adjusts the timing to avoid damage. This can affect acceleration, causing the vehicle to feel sluggish.

Check your owner’s manual or the fuel cap to see what to use. If there’s no indication, regular grade (87 octane) is fine. If it says “Premium Recommended,” you can use regular, but will get better performance on premium (although, on many vehicles, the performance difference will be slight). If it’s “Premium Fuel Only,” go for that. And any time you hear knocking or pinging, or if your vehicle feels sluggish, try moving up a grade.

How Do I Know Which Side the Fuel Door Is On?

You probably know from experience on the vehicle you own, but maybe you’re in a brand-new car or a rental and you’re not sure. Look at the fuel gauge. Most will have an arrow, which indicates if the filler is on the left or the right.

A while back, a story made the rounds on the Internet that if your gauge didn’t have an arrow, there was still an indication, secretly stashed in the little picture of the fuel pump beside the gauge. If the nozzle was on the left side of the pump, your fuel door was on the left side of the vehicle, and same for the right side. Alas, it’s not true. You always have a 50/50 chance, and if your pump icon’s nozzle does line up with your car’s correct side, that’s just a coincidence.

One thing to remember is that if you ever borrow or rent a car, how you open the fuel door is not universal. On some cars, you just press on it or pull it open; on some, the vehicle must be completely unlocked before pressing the fuel door will work; and on others, there’s an interior toggle or button to unlatch it, some of which can be hard to find (these can be on the floor beside your seat, in the door panel, or on the left-hand side of the dash). Before you drive away from the rental agency, be sure you know how yours works.

How Does the Gas Pump Know When to Stop?

It’s like magic: even though you’re holding the handle open, it shuts off when the tank is full. The secret is in the tip of the nozzle – look closely, and you’ll see a small hole.

There’s an equally small pipe attached to that hole, and it goes back to the handle. As fuel goes into the tank, it displaces air, which flows up through the tube. As soon as the gas level rises into the filler neck and reaches the hole, it creates a vacuum in the tube, which triggers a switch to turn off the fuel flow.

The Real Reason Not to Use Your Phone When Filling Up

You’ll notice a list of several rules posted on the pump, including not allowing children to use it, and how to fill a portable gas can. But there’s also one about not using a cellphone while you’re pumping your gas, and it’ll often add that it’s because a spark can cause a fire.

The rule isn’t about the phone itself – the chances of it giving off a spark are slim to none – but rather, it’s about the distraction. People talking or texting on cellphones aren’t paying attention to what they’re doing. If they’re moving around, especially if they get in and out of the car, it can generate static electricity, which can create that unwanted spark. They might also not realize they’ve spilled gas, or they forget to remove the nozzle, or anything else equally important. Don’t ignore the warning because you know your phone won’t spark a fire; leave it in the vehicle until you’re done filling up.