It’s easy to overlook your gas cap—after all, it’s just a small plastic piece you twist a few times after fueling up. But that simple cap plays a major role in fuel efficiency, emissions control, and even how much you pay at the pump over time. Ignoring a faulty or loose gas cap can cost you more than you think.
Here’s why your fuel cap matters and how to avoid losing money (and mileage) over something so small.
What Does a Fuel Cap Do?
The fuel cap seals your gas tank, preventing fuel vapors from escaping and keeping air and contaminants out. It also helps maintain the correct pressure in your fuel system, which is crucial for your engine to run efficiently.
A missing or loose cap disrupts this system, leading to:
- Increased evaporation of fuel
- A triggered “Check Engine” light
- Decreased fuel economy
- Potential emissions test failure
According to the U.S. Department of Energy, a faulty gas cap can allow up to 30 gallons of fuel per year to evaporate. At $3.50/gallon, that’s over $100 lost—just from vapor.
Common Warning Signs of a Bad Fuel Cap
- Check engine light turns on shortly after fueling
- Strong gasoline smell near the car
- Clicking sound is missing when tightening the cap
- Visible cracks or warping in the cap or seal
If your vehicle uses a capless fuel system (common in newer models), make sure the flap mechanism closes properly after each fill-up.
How to Prevent Fuel Cap-Related Waste
- Tighten until it clicks: Most fuel caps require three clicks to seal properly.
- Inspect regularly: Look for signs of cracking, damaged threads, or a loose seal.
- Replace if necessary: Gas caps are inexpensive and easy to replace. You can find vehicle-specific caps at auto parts stores or online via retailers like AutoZone or Advance Auto Parts.
- Address dashboard alerts quickly: Don’t ignore your check engine light if it appears after refueling—it could be a simple cap issue.
Fuel Cap Issues and Emissions
Your gas cap is also a critical part of your car’s evaporative emissions control system (EVAP). Leaks from the fuel system, including the cap, allow hydrocarbons to escape into the air, contributing to smog and air pollution. In many states, a faulty gas cap will cause you to fail emissions testing during annual inspections.
Extra Tip: Pair Fuel Efficiency with Smart Savings
While keeping your gas cap secure is important for fuel economy, it’s just one piece of the puzzle. Combine good car habits with smart tools like GasBuddy for price tracking or cashback platforms like Fluz to offset your fuel costs with gift card cashback at stations like BP.
Final Thoughts
Don’t underestimate your fuel cap. A small twist of plastic could be the reason you’re losing gallons of gas and spending more than you need to. Checking and replacing a faulty cap is fast, easy, and one of the most affordable ways to improve your car’s efficiency.
