AUTONEWS

Is it a mistake to fill your tank to the top when it's hot? Here's what the experts say

With the arrival of summer and high temperatures, the advice that drivers often hear is becoming more relevant again - that during the heat you shouldn't fill your tank to the top because gasoline and diesel expand due to heat, which supposedly can pose a risk. But what is actually true, and what is just a myth?

The short and clear answer is - yes, you can fill your car or camper to the top quite normally, even in extreme summer temperatures. The key problem, however, lies not in the concept of a full tank itself, but in what drivers mean by "filling" and the dangerous mistake that many of them repeatedly make at gas stations, reports Autonews.

As long as you fill your car only until the pump nozzle automatically "clicks" and stops the fuel flow, you are completely safe - even if it's 35 degrees Celsius outside.

A serious problem and technical risk only arises when drivers, after that initial automatic shutdown, continue to manually squeeze the gun and “round up” the amount on the display, trying to squeeze in a little more fuel. Vehicle manufacturers, mechanics and technical institutes unanimously warn against this very practice, reports Feniks magazine.

3 Key Facts About Fuel Expansion During Summer Heat

Fuel is cold in the ground, it only expands in the car:

The biggest misconception is that gasoline or diesel heats up and expands inside the gas pump or in the hose. The truth is that fuel in underground gas station tanks remains relatively cool even during the hottest summer days. The process of volumetric expansion only begins after the fuel reaches your car’s tank, where it is quickly heated by solar radiation, hot asphalt and the heat of the engine itself.

What is the purpose of the expansion space:

The automatic closing of the fuel nozzle not only signals that the tank is full, but also ensures that there is exactly as much free space inside the tank as the car manufacturer intended for expansion. This empty safety part serves as a reserve for the accumulation of accumulated fuel vapors and for the inevitable expansion of gasoline or diesel due to an increase in temperature. When the temperature rises, the fuel can expand freely without leaking or overloading the ventilation system.

Pouring in “excess” destroys the filters:

If you continue to fill the tank after the first click, you gradually fill this strictly defined safety space. Depending on the vehicle model, up to 17 additional liters of fuel that should not be there can be squeezed into the expansion spaces and supply pipes. When the tank is so full that it heats up in the sun, the fuel has nowhere to go, so it starts to leak or goes directly into the evaporation system, which is designed exclusively for collecting gas vapors. This creates a huge load and permanently damages the activated carbon filter and other sensitive purification components.

Exactly how much do liters of gasoline and diesel expand in the heat?

That the expansion of liquids in the summer heat is not negligible is best shown by accurate physical calculations depending on the volume of the tank and the temperature jump in degrees Celsius.

Calculations show that in larger tanks of 80 liters (often found in large caravans, SUVs or campers), gasoline can expand by almost 3 liters if the temperature rises by 30 degrees. If you have eliminated the expansion space by manually filling the tank, this volume will create dangerous pressure. So, on your next summer trip to the coast, remember the golden rule: as soon as the nozzle makes the first automatic "click", refueling is finished!

Is it dangerous to fill up your car with petrol on a hot day?

Rumours online fanned fears that hot petrol tanks can explode if filled to the limit.

The message claimed five cars exploded in a week due to being filled up when the cars were hot.

But this was debunked as false, as experts confirmed there’s no danger in filling up your car with petrol on a hot day.

The message has reportedly been around for years, and simply re-emerges each time a heatwave hits.

What is the truth about filling your car up on a hot day?

Experts said there’s “no truth in this” rumour.

Fuel systems are designed to cope with vapour coming from the fuel and there’s no risk of an explosion.

Drivers shouldn’t worry about filling their tanks to the top.

And in fact, they’re advised to do so – as the danger of running out of fuel is greater than the car exploding on a hot day.

Rod Dennis, RAC spokesperson, said last summer: “There is no truth in this.

“All fuel systems on passenger vehicles are designed to cope with any expansion of fuel, or vapour coming from the fuel.

“There is no risk of explosion from filling up a fuel tank fully and drivers should have no concerns in doing so.”

The AA confirmed the worrying message was an old false story.

They revealed cars are tested in weather extremes to be able to cope with hot and cold temperatures.

But what can damage your car on hot days?

Extreme temperatures won’t just give you sunburn and melt roads, but they also risk causing severe damage to your car.

Easily maintainable car parts threaten to shut down under the sweltering sun as disinterested drivers fail to look after their motors.

Oil and engine coolant are also under threat from soaring heat while fuel consumption is likely to increase.

Overheating brakes – or “fading” – can increase stopping distances and in worst cases lead to total brake failure.

Driving on under-inflated tyres in high temperatures can accelerate the chances of a blow-out by 60 per cent, too.

And engine performance can dip by 15 per cent – even more if it’s running the air conditioning.

Yes, it is a mistake to force extra fuel into your car after the pump clicks off. "Topping off" fills the crucial air gap required for fuel expansion in hot weather. This can push liquid gasoline into the vehicle’s evaporative emissions system, causing hundreds of dollars in damage.

The automatic shut-off on a fuel nozzle triggers when the tank is full, but it deliberately leaves some empty space at the top. This space is essential because gasoline expands as it heats up or warms inside a hot vehicle.

When you bypass that automatic stop by "topping off," you risk the following:

Evaporative system damage: Liquid gas can flood into the vapor recovery system (specifically the charcoal canister), ruining the filter. This frequently triggers your "Check Engine" light and can lead to expensive repairs.

Fuel spills: Liquid fuel can expand and spill out of the tank, creating a fire hazard or damaging the vehicle's paint.

The "explosion" myth: While overfilling can cause damage or leaks, modern fuel systems are highly pressurized and sealed, meaning you do not need to worry about your gas tank exploding in the summer heat.