Over Filling Your Gas Tank is a Bad Practice to Have
Timothy Boyer's picture

Do Not Buy a Used Rental Car for This Reason

Buying a rental car is typically advised against because of poor maintenance by rental agencies and because some renters…quite frankly…abuse rental cars. However, there is another reason why buying a used rental is a bad idea due to a shared fault of both the renter and the rentee.

The Problem with Rental Cars

Earlier we had discussed the commonsense recommendation against buying a used rental car: they go through more drivers than any other used car out there and are not always well-maintained by the rental agency. In addition, we know that not all drivers will treat a rental vehicle like they should and will in fact “drive the crap” out of a rental---because they can.

However, there is another reason for avoiding buying a used rental car---abuse at the gas pump.

If you have ever gone on a road trip or tried to squeeze as much discounted gas out of a pump as possible into your tank, then you are probably guilty of making a common gas pump mistake that could cost you several hundred dollars in repairs---over-filling or “topping off” your gas tank.

The problem with this practice is that over-filling your gas tank can cause damage to your vehicle’s evaporative emissions (EVAP) system.

Reportedly, cars sold since 1971 are designed with a closed-circuit system to trap and later burn fumes from the gas tank. This system consists of charcoal canisters, tubes, valves, and sensors designed to handle gasoline vapors…but never liquid fuel. Therefore, over-filling your tank can route the liquid portion into the vapor portion of the system.
Doing this a few times might not have much effect on a car; however, doing this repeatedly increases the likelihood your car will develop problems that could cost you hundreds of dollars or more to repair.

Here's a Scotty Kilmer explanation of why over-filling your gas tank is bad for your car. Please note that you only need to watch the first 65 seconds of the video to get the relevant info.

Never Do This When Filling Up at the Gas Station

What This Has to Do with Rental Cars

One of the banes of an airport rental is the crazy policy of having to return the vehicle with a full tank of gas. In some cases, if you are even a hair under full according to the fuel gauge, you can be charged for a full tank of gas---at the rental agency’s gas prices!

Related article: How Car Rental Companies Scam People Out of Money

Part of the problem of ensuring that the vehicle is returned full is that it always seems like the fuel stations are either (1) on the wrong side of the road on the way back or (2) far enough away the airport to cause your fuel needle to dip just below the full mark.

This can be especially irritating when the car rental agent gets into argument with you over what a “full tank of gas” really means. I’ve even had one argue with me that “full” means the needle has to be above the full mark because the tank physically holds more than what the needle says---yeah, that kind of sound reasoning.

Related article: Car Renters Risk Arrest Because of This Rental Agency’s Policies

Anyway, the point is that these kind of fuel shenanigans encourage rentees to overfill the rental gas tanks just to ensure that they will avoid a bogus fuel charge by the rental agency. This means that if everyone does this when renting a car, that the car may wind up on the used car lot with an EVAP problem that gets passed onto the car owner.

Related article: Red Flag Used Car Dealers Do Not Want Buyers to Know About

Symptoms of a Damaged EVAP system:

• Poor Gas Mileage.
• Poor Engine Performance.
• Rough Idling.
• Difficulty in Starting Up the Engine.
• Engine Check Light Turns ON.
• Gas Odor.
• Gas Tank will get difficult to fill up.
• Failed Emission Test.

And finally…

For additional articles about buying used cars, here are some selected articles to help you avoid a problem car:

Toyota Dealership Shows What Really Happens When Previously Owned Cars Are Inspected and Certified

Car Lawyer Explains Myths, Scams, and Risks of Buying a Used Car

Scam Alert: What Dealerships Don’t Want You to Know About Used Car Inspections

COMING UP NEXT: Why You Should Not Buy an EV Today

Timothy Boyer
is a Torque News automotive reporter based in Cincinnati. Experienced with early car restorations, he regularly restores older vehicles with engine modifications for improved performance. Follow Tim on Twitter at @TimBoyerWrites for daily new and used vehicle news.

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