Symptoms of a Loose Gas Cap

Symptoms of a Loose Gas Cap

12th Feb 2021

fuel cap on car

Problems caused by a Loose Gas Cap

A loose gas cap is a common problem encountered by drivers. Assuming your vehicle has a combustion engine -- as opposed to an electric engine -- it will have a gas cap. Typically consisting of a plastic cap with a gasket, it's designed to seal the gas tank so that neither liquid gas nor fumes can escape. Over time, however, gas caps can fail. Rather than providing an airtight seal, they'll leak. Below are some of the most common symptoms of a loose gas cap.

Gas Odors

A telltale sign of a loose gas cap is gas odors. If you smell gas odors while driving your vehicle, a loose cap is probably to blame. When the gas cap is loose, gas vapors will leak from the tank. These gas vapors will then manifest in the form of gas odors, which you can smell while driving or walking around your vehicle.

Poor Gas Mileage

You'll probably get poorer gas mileage when driving if your vehicle has a loose gas cap. Gas vapors are combustible. They provide the fuel your vehicle's engine needs to generate combustion. A loose gas cap will leak gas vapors so that your vehicle has poorer gas mileage.

Because of its impact on gas mileage, a loose gas cap will cost you money. You'll have to fill up more frequently, resulting in higher gas costs.

Doesn't Tighten Completely

If your vehicle's gas cap doesn't tighten all the way, it's probably loose. Most vehicles are designed with gas caps that require a minimum number of "clicks." In other words, you'll have to tighten the gas cap by turning a specific number of times, such as three times. If you're unable to tighten it completely, it will remain loose.


Another common symptom of a loose gas cap is the Check Engine Light (CEL). As part of the emissions system, the gas cap can trigger the CEL if it's loose. Your vehicle's onboard computer will detect the loose gas cap. Upon detecting this emissions problem, it will trigger the CEL.

While a loose gas cap poses many different problems, it's a quick and easy fix. All you have to is buy a new gas cap with which to replace it. Gas caps become loose when their inner gasket fails. With a new gas cap, the gasket will be fresh so that it properly seals your vehicle's gas tank.