What Happens If You Overfill Your Gas Tank
We know what you’re thinking: surely people aren’t overfilling their gas tanks, but it can happen, it’s more common than you think, and it can affect you. If you do overfill your gas tank, or are driving in a vehicle that has been overfilled, what should you do? In this article we will look at what happens if you overfill your gas tank, the symptoms of overfilling a gas tank, and what you can do to fix them.
This article focuses on what happens when you overfill a gasoline-powered vehicle, and is not to be used as a reference when discussing a diesel vehicle, due to differences in the fuel characteristics and fuel systems.
How Does An Overfilled Gas Tank Happen?
We have all been there; you are filling your tank, and you get that click from the pump. Some people will leave it at that and hang the pump back up, but others will continue trying to fill up. The most common time you’ll see an overfilled gas tank is when there is an incentive for the person to fill as much as possible. For example, if there is going to be a jump in fuel prices coming up because of tax changes, or a change in the price of oil. People who want to get their money’s worth will fill their tanks to the brim, and oftentimes exceed the maximum capacity. Similarly, certain apps and credit cards offer deals on certain gas station chains, which again entices people to overfill their gas tanks as they might not see that brand of gas station again on their travels.
Another situation where cars can be overfilled is with fleet vehicles. If you don’t have to pay for fuel, you will obviously fill up as much as humanly possible so you don’t have to fill up again. Even if you don’t think you will do that, if you rent a car or van, this can still affect you, with the staff sometimes overfilling the car’s tank. People don’t tend to care as much about a vehicle’s maintenance or needs when they don’t own it or need to pay for it, so a lot of people will continue to fill up after the pump clicks.
The last way an overfilled gas tank can occur is due to a faulty pump air pressure sensor that doesn’t activate when you are getting close to your tank’s limit. If you are not paying attention, or do not know your car’s tank capacity, this can lead to overfilling.
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Symptoms Of An Overfilled Gas Tank
Decrease In Performance
Believe it or not, too much fuel is a bad thing. An overfilled fuel tank can cause issues with both your fuel pump and, more critically, your injection system. If your car detects an overfilled gas tank, it may limit power and torque for a period until the excess gas is burned off, or until a check engine code is cleared.
Overfilling Can Cause A Range Of Engine Lights
If you seriously overfill your vehicle, you may be greeted with multiple engine lights depending on how advanced your car’s emissions system is. Unlike diesel, gas is a volatile liquid (i.e. it evaporates easily) and, as such, your gas tank has systems in place to deal with the vapors and expansion of fuel in hotter weather. Overfilling can saturate these systems with fuel instead of vapors, causing major issues. This will manifest itself initially with emissions and engine warning lights, and, if it is bad enough, it can cause the vehicle to go into limp mode.
Potential Issues When Filling In The Future
If you are the kind of person who constantly tops off your fuel tank, instead of running the tank down, you may run into issues when filling up. Major signs of this include the fuel tank vent tube getting clogged with fuel, causing fuel vapors to escape. This can create a smell of fuel in and around the vehicle and, more importantly, can cause a fire hazard. In extreme cases, usually caused by heat, the fuel can expand and it can actually spray out of the gas tank filling hole.
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What Damage Can Be Caused By Overfilling Your Fuel Tank?
As previously mentioned, in extreme cases, overfilling can actually damage parts of your car’s EVAP system. So what exactly can happen, and how much does it cost to put right?
Vapor Charcoal Canister
The charcoal canister is part of your car’s emissions system and its job is to neutralize the pollution caused by the vapors that can escape from your fuel tank. It traps these vapors and passes them back into the engine to be burned off. If you overfill your fuel tank, the lines that run from the tank to the canister can be filled with fuel, with the canister quickly becoming saturated. This can cause a whole host of issues with the engine and emissions systems, as not only is the canister being damaged, but it is reportedly a very hard thing for a mechanic to diagnose once it fails. The hypothetical savings you made at the pump will usually not be able to offset the $800 it takes to repair the charcoal canister.
Damage To The Purge Valve
The purge valve comes after the charcoal canister, usually comprising an electric solenoid that releases the vapors into the engine. For some makes and models, these purge valves can have issues at the best of times, so adding the issue of a damaged charcoal canister will increase pressure on the purge valve, and it could fail prematurely. A failed purge valve can cause rough idling, sluggish performance, and usually a check engine light. In some very extreme cases, a crack in the purge line, mixed with the excess vapors caused by an overfilled tank, can create a fire hazard as the vapors leak into the hot engine bay.
Potential Damage To Your Catalytic Converter
In some cars with more rudimentary EVAP systems, or if the charcoal canister is only damaged and not fully saturated, the engine may run rich. An overly rich fuel burn can damage your catalytic converter. This can be a costly mistake with a catalytic converter replacement setting owners back at least $800, but usually upwards of $1000.
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What To Do If You Overfill Your Tank, And How To Prevent Doing So In The Future
So you have overfilled your gas tank by accident, now what? If you have filled it to the point that fuel has spilled out onto the gas station forecourt, inform a member of staff about the fire hazard and make sure you and your vehicle have not been covered in excess fuel. Thankfully, in terms of your car, in the vast majority of cases, you shouldn’t even be able to overfill it to the point of damaging your vehicle, with the pumps having an automatic cut-off when too much pressure is detected. If you continue to fill past this somehow by bypassing this safety feature, then you may run into issues. If you do it once, there is a chance you may get away unscathed, but don’t take that risk.
Take the car on a good long drive to burn off some of that excess fuel. The last thing you want to do is overfill and then park up, causing a build-up of excess vapors. If, during the course of this drive, you don’t feel any unusual activity or suffer any check engine lights, then you should be fine. Secondly, it is recommended that you don’t fill the tank soon after an overfill happens, with manufacturers strongly recommending against “topping off” the tank constantly.
Lastly, the largest takeaway from all this is just not to risk your EVAP system for a few extra miles. Any savings you make at the pump when you push past that cut-off click will be quickly negated by the damage you do to your vehicle, and the time and money wasted getting it fixed.
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FAQ
Is it harmful if I put too much gas in my car?
Yes, you can damage your vehicle’s EVAP system, causing multiple engine lights, a loss of power, and costly emissions system repairs.
What are manufacturers’ feelings about overfilling/topping off your fuel tank?
Both manufacturers and dealers strongly recommend against overfilling or topping off your tank.
What can I do to avoid overfilling my gas tank?
Just stop filling when the pump clicks. Make sure when you’re filling your tank to be mindful of your tank’s capacity, as if the pump is faulty it could overfill.
