Gas Cap Toolkit: “Testing Vehicle Gas Caps for Leaks”


Vehicle emissions are the number one cause of ground level ozone. A Gas Cap Check and Replacement Event is an event that reduces the amount of emissions emitted by vehicles by ensuring that a vehicle’s gas cap is working properly. This event has the potential to improve air quality and fuel economy in less than 5 minutes per vehicle.

What is a “Gas Cap Check and Replacement Event?”

tl_files/cfca/images/gas_cap_check/gas_cap_testing.jpgA Gas Cap Check Replacement Event is designed to reduce the amount of emissions a vehicle emits by testing a vehicle’s gas cap to make sure it is in good working condition. The equipment can determine whether or not a gas cap needs to be replaced by testing the air pressure around the cap. Gas caps are given a grade of pass or fail and if the gas cap fails, it is replaced for free. This process takes less than 5 minutes to complete per vehicle and can prevent the cap from leaking fumes into the air.

This event can also be partnered with a “Tire Pressure Check”, since tire pressure is also related to fuel economy. A “Tire Pressure Check” checks tire pressure to ensure it is appropriate for the particular make and model of the vehicle.

At this event, educational materials are provided that focus on local air quality, importance of vehicle maintenance, and health effects related to emission pollution. Also, as incentive to encourage proper vehicle maintenance, promotional give-aways like tire pressure gauges provide drivers with a handy way to make sure their tires are always properly inflated.

Why does replacement of leaking gas caps contribute to fuel savings and air quality improvement?

tl_files/cfca/images/gas_cap_check/KKD display with person.jpgUp to 30 gallons of gasoline can escape from a leaking gas cap, and depending on current gas prices, the expense could be more than most can afford to lose. This is why it is important to have a properly fitted gas cap to ensure that gasoline and money can be saved.

Also, these 30 gallons of fuel become 200 pounds of emissions that directly affect your local air quality. Issues such as idling and leaking gas caps cause emission related pollution making vehicles the number one contributor to ground level ozone.

Low tire pressure can also affect a vehicle’s fuel economy. Gas mileage can decrease 4% for every missing pound of pressure, so it is important to have tires properly inflated.

How should a group go about planning a Gas Cap Replacement Event, or an “Emissions Reduction” Event?

This type event is typically run by staff and/or volunteers who either have careers or an interest in air quality, fuel economy and other local environmental issues.  A gas cap event requires purchase or borrowing of specialized testing equipment, proper training of staff/volunteers, and significant time and effort for planning, promoting and conducting the event.  It is recommended that any organization interested in such a program either partner with someone that wishes to loan out their equipment (such as the Center for the Environment, or Charlotte Mecklenburg Air Quality), or look into grants and other funding to purchase their own, if they have available staff and resources.
There are several types of groups in which volunteer helpers can be found to assist with gas cap events. A local state air quality coordinator would be a good resource for information.  Also, city or county sustainability groups are a good resource for finding interested volunteers who want to be involved in community events.   In addition, community colleges that have an automotive department may have an interest in volunteering and could provide some of the needed equipment.
Once equipment and helpers are identified, the easiest way to plan the actual event is to look for community events that are already pulling together large groups of people, such as an “Earth Day” Event or Employee Health Care (Wellness Fair) Event. Any community event that has a large parking lot with a constant flow of people is a good place to start. If a community event is not available, then places that have large parking lots with daily visitors should be taken into consideration, such as schools and large employers.


What types of locations are best suited to such an event?

tl_files/cfca/images/gas_cap_check/Gas cap photo of display June 25.JPGLocations where cars are already parked or are in the process of arriving are ideal for this kind of event.   Community events such as: fairs, festivals, church fundraisers and volunteer car washes are great places to start a gas cap check and replacement event, because cars will already be in the area.    Also, special venues such as apartment complexes, major arenas, baseball stadiums, major employers, YMCAs and libraries, can be great places to find a parking lot full of cars.

What methods are available for testing gas caps?

tl_files/cfca/images/gas_cap_check/Gas_cap_tester.jpgThe first method for testing gas caps is using an open parking lot where you can create lanes of traffic for vehicles to drive up and be checked. The number of lanes needed depends on the traffic flow of the event. For most events two or three lanes are enough. At each lane you would have one volunteer who gathers information on the vehicle (make, model, year), while the second volunteer is testing the gas cap.  This method is good for low attendance events, or where the vehicles are trickling in over time at a slow rate.  You can have the driver stop their engine, pull to the side, or just sit in line, if not blocking a roadway.  Make sure the driver does not idle, as this sends the wrong message.

If you decide to do a tire pressure check at the same time, then you will need a third and possibly fourth volunteer to test tires, and let the driver know if they need adjustment. If you decide to also have a compressor onsite to adjust tire pressure, you may need at least 2 additional helpers. 

The second method for testing gas caps is to utilize permission slips that ask the driver to “pop” their gas cap door, so the volunteers can walk through the parking lot and test at a later time. Permission slips are a great way to hand out information while allowing the volunteers to see whether or not a driver wants a cap tested.   If a driver has given you permission to check a gas cap, the “permission slip” should be visible in the dashboard and the gas door should be accessible.    If the cap fails, then the volunteer can place a note or flyer on the windshield saying that the cap has been replaced.

At most events you will find that a mix between both methods is best.

At most events, between 7-10% failure can be expected.   However, do not be fooled by the year of the vehicle!     A “new” car can have a faulty gas cap due to improper replacement of the gas cap after re-fueling, or general wear and tear.   Also to much surprise, “older” vehicles may have passing gas caps.   If a vehicle fails, or is on the border-line between pass and fail, it is recommended that the cap is tested again before replacing.

What type of training for Gas Cap volunteers/workers is required?

Before the day of the event, volunteers need to be trained on how to use the gas cap equipment. The equipment will come with a manual that should be skimmed and tabbed for critical quick reference pages.  Templates and instructions are located in this toolkit to serve as quick “cheat sheets” that can also be printed and used the day of the event. Volunteers need to be prepped on what to ask drivers when they pull through the drive thru lane, and prompt them to open their gas door. The questions that need to be asked are on the “vehicle log sheet” in this toolkit, so if the gas cap fails, it can be correctly replaced. Urge drivers to participate by informing them how “quick” a gas cap check can be and how it can save them money.

The location site should be visited in advance of the event, so that the volunteers can decide on the best location for setup. Think about traffic patterns, and minimize traffic back up, by having more volunteers at the greeting line to direct traffic and encourage drivers to stop.

tl_files/cfca/images/gas_cap_check/gas_cap_tester_in_use.jpgWhat is the needed Gas Cap Equipment, where do I obtain it, and how much funding will be needed to purchase the equipment?


If you are an organization that intends to do long term gas cap testing and have the available funding to purchase equipment, you will need gas cap testers, adapters and an assortment of replacement caps. The type used by the Center for the Environment is Stant 12370 Mechanical Fuel Cap Tester System & set of adapters, which costs approximately ~$1,500.  An assortment of typical replacement caps (~160 total) costs approximately $1,000, for a total estimated budget of $2500-$2600.  
 If equipment can be borrowed or shared (partnering) with an organization that already has the necessary equipment, then additional replacement caps would only be needed, and the cost is low (~$8-10 per cap).

They can be purchased from Uniselect, by contacting Cliff Chambers 704-578-5255.

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