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'I Just Apologized To My Car': Do You Always Top Off Your Tank? Mechanic Says This Honda Civic Is Proof You Shouldn't

"Very expensive..."

Mechanic Says This 2016 Honda Civic Is Proof You Shouldn’t top off your tank

Photo by: fedsmademewrench & Eli Clouse

Stacy Fernandez

By: Stacy Fernandez

Nov 24, 2025 at 2:00pm ET

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Most drivers have done this: stand at the pump and squeeze the trigger a few extra times after it clicks off, trying to round up to an even dollar amount or just squeeze in a bit more fuel.

While it seems harmless enough, it isn’t. A mechanic's latest repair job shows how doing that over time can lead to an expensive repair bill that has nothing to do with your engine.

In a viral video with more than 533,000 views, mechanic Trez (@fedsmademewrench) reveals the very real consequences of being a chronic gas tank over filler. In this case, the person breaking the gas filling rules drove a 2016 Honda Civic.

"Are you the person at the gas pumps that's constantly trying to top off their tank when it's full? This video is for you," Trez starts.

Trez shows that the Civic arrived at his shop with multiple failure codes for the EVAP emission system—P04F1 low purge flow detection, P0441 purge flow malfunction, P1454 sensor circuit range/performance problem, and P04DF high purge flow detected.

The customer had already attempted to resolve the issue by replacing the purge valve, but that solution was unsuccessful.

To finish his analysis, Trez disconnected the vapor feed line that runs to the fuel tank and stuck a small camera inside to inspect it. Through the camera, he could see significant debris throughout the line, showing there was clearly something wrong with the system.

Using an exploded diagram of the EVAP system, he walks viewers through exactly what happens when drivers repeatedly overfill their tanks.

"So when you are full of gas and you're up here clicky clicky clicky, this little one-way valve here is gonna have a little bit of gas intrude into its line," Trez explains.

The problem is that the EVAP system is designed only for vapor, not actual liquid fuel. When drivers keep clicking the pump after the automatic shutoff, they're forcing liquid gasoline into a system that can't handle it.

"So once a little bit of liquid fuel makes it all the way in here, this is inside the canister, and that's when things start to go south," he says. "This causes the filter inside to deteriorate and start to clog the lines. And that's why a purge valve did not fix this customer's car."

In the caption, he adds, "A lil PSA for all the gas pump clickers out there, every time you force gas into the tank when it’s full, it’s going places it should not go! Charcoal canisters are very expensive to replace! Save your canisters! Keep in mind this is something that happens after constant overfilling every time you visit [a] gas pump."

Gallery: 2025 Honda Civic Si Review

2025 Honda Civic Si Review

Source: Jeff Perez / Motor1

What Is the EVAP System and Why Does Topping Off Damage It?

Your car's EVAP (Evaporative Emission Control) system exists primarily to trap fuel vapors and prevent them from entering the atmosphere, CarParts.com explains.

When your engine is off, fuel vapors from the gas tank are stored in a charcoal canister. When conditions are right, a purge valve opens, and those vapors get drawn into the engine to be burned during normal combustion.

This system is designed only for vapor, not liquid fuel, so when liquid gasoline enters the system, it saturates and breaks down that charcoal filter, causing debris to clog the lines throughout the system.

What Drivers Are Saying

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When you keep clicking the pump nozzle after it automatically shuts off, you're forcing fuel past the one-way valve that's supposed to keep liquid out of the vapor lines. That liquid fuel goes where it’s not meant to be, contaminating components that cost hundreds or even thousands of dollars to replace.

Replacing a charcoal canister can cost upwards of $600 or more, according to RepairPal.

And unlike a loose gas cap—the most common cause of EVAP codes—a contaminated canister can't be fixed with a quick tightening or a $20 replacement cap.

People Feel Attacked by the Mechanic’s Advice

Judging by the nearly 800 comments as of this writing, most people top off their tanks when they fill up with gas.

“Bro why do you have to call me out like that wtf. all I'm doing is trying to round off the dollar amount to an even number,” one wrote.

Said another, “I just apologized to my car.”

One pointed out that topping off doesn’t add enough fuel to make much of a difference.

“Never understood topping off the tank anyways. You get what? Maybe an extra 1/4 mile. What’s the point,” they wrote.

Some people aren’t exactly buying Trez’s advice.

“Been doing it for 40 years; never had a single issue,” wrote one. A second agreed, “Done this forever on all my cars and trucks, never an issue lol.”

A few, however, suggested that they would be changing their habits in the future.

What do you think?

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Comments

“No more clicky clicky.....got it,” vowed one.

Motor1 reached out to Trez for comment via TikTok direct message and comment. We'll update this if he responds.