(Updated on May 19, 2020)
Have you ever gone out to your car in the morning and noticed a strong gasoline smell in the cabin? Perhaps the smell only occurs after you start the car or open the hood?
A strong fuel smell around your vehicle is never a good thing, but some causes are worse than others. If you are experiencing a strong fuel odor around your vehicle, it is best to resolve the issue as quickly as possible.
Common Causes of Your Car Smelling Like Gas
1) Vehicle is Running Rich
When you first start the car in the morning, your car probably emits a strong gasoline smell from the tailpipe. This is fairly common and usually a result of normal operation.
Vehicles often run rich on startup to achieve the proper air fuel mixture. The combustion environment is different on a cold engine than one that is running at operating temperature.
This rich fuel smell should go away after the car has warmed up. If it does not, you may have another issue on your hands. Some vehicles run rich persistently due to a mechanical issue, such as incorrect cam timing, a bad spark plug, or a bad O2 sensor.
A cylinder with a bad spark plug will still inject fuel, despite receiving no spark to combust the fuel. This unburnt fuel exits the exhaust and will either ignite with the hot exhaust gasses or dump out of the tailpipe.
The ECU has a bit of smarts, but not much; the engine computer usually can’t tell when a spark plug has failed due to wear.
2) Old or Poor Quality Gas
Gasoline deteriorates over time, gradually losing its combustibility. As it breaks down, old gasoline may smell pretty foul. If it’s been a while since you visited the gas station, your fuel quality may have suffered due to age or water in the gas.
For a near empty tank, you could try simply filling the tank with fresh fuel to dilute the bad stuff. If the fuel has been sitting in the tank for many years, it might be a good idea to drain the tank before filling it.
3) Evaporative Emission Control System (EVAP) Leak
Gasoline has a very low flash point of -45° F (-43° C). Above this temperature, gasoline will produce flammable vapors that could ignite in the presence of a spark or a flame.
The EVAP system is designed to catch and contain these vapors. This keeps them in the fuel system so they don’t leak into the atmosphere (or your garage).
If the EVAP system detects a leak, you will likely notice a check engine light related to the system. Sometimes this code is simply triggered by a gas cap that wasn’t screwed on tight, but it could also indicate that these harmful vapors are escaping the fuel system in other ways.
If you do notice a fuel smell around your vehicle, try scanning the vehicle for codes as one of your first steps. This may help you narrow down the problem considerably.
4) Flooded engine
If you attempt to start the car but there is no spark, the injectors will still pump fuel unless they are disabled. This unburnt fuel can sit in the combustion chamber or the exhaust system, causing the car to smell like gas.
Continued attempts to start the vehicle will only exacerbate the problem until the excess fuel is cleared from the engine.
There may be a legitimate need to crank the engine without starting the car. For instance, this is done while performing a compression test.
Some cars allow you to disable the fuel system by holding the throttle open while cranking. Others require you to pull the fuel pump relay. Consult a repair manual for the correct procedure to disable the fuel system.
5) Fuel Leak
A fuel leak is never a good thing. In the best case, you’ll experience worse fuel economy. In the worst case, the leaking fuel could ignite and cause a fire while you’re driving the vehicle. Here are some common places you may want to check to see if you have a fuel leak.
The simplest reason you may have a fuel leak is a poor seal between the gas cap and the gas tank. Check to make sure the cap is tightened down all the way. You will hear the cap start to click when it’s tight enough.
If the issue persists, the seal under the gas cap may have gone bad. You may be able to replace just the seal, or you may have to replace the whole gas cap. Either way, it’s a cheap and easy fix.
Rubber Fuel Hoses
Rubber fuel hoses are very durable, but they will still degrade over many miles. If an old hose gets soft and spongy or too hard and brittle, it could rupture and cause a fuel leak.
A pressurized section of the fuel system will cause gasoline to spray out of a pinpoint hole with considerable force. If this spray reaches a hot part of the engine such as the exhaust manifold, it could easily start a fire.
There are fuel hoses throughout the vehicle. Rubber fuel hoses often link to hard metal lines that run the length of the car from the gas tank to the engine bay.
Fuel hoses are most likely to leak around connections, so check these areas first. Sometimes the rubber will deteriorate and you will notice a leak in the middle of one of these hoses as well.
If you have an older vehicle, it may be wise to have a full fuel system inspection performed to pinpoint the exact location of the leak and to replace any hoses that look like they’re on their way out.
The charcoal canister (also called a carbon canister) is the part of the EVAP system that catches and contains fuel vapors. A leak in the charcoal canister or one of the hoses connected to it would cause a fuel smell in the engine bay.
If the charcoal canister is leaking, you may need to replace it. On the other hand, it could simply be one of the attached fuel hoses leaking instead.
On port injected vehicles, fuel is introduced into the engine via the intake manifold. Many engines will have several fuel lines that mate up with the intake manifold.
Check the condition of these lines to see if there is any evidence of leaking fuel, both at rest and while the engine is running.
Fuel Injectors/Fuel Rail
Fuel injectors are attached to a fuel rail and seal against the intake manifold via little o-rings. When these o-rings deteriorate, fuel can leak past the injectors and onto the intake manifold, instead of into the combustion chamber.
Fuel filters remove particles and contaminants from the fuel system so only clean gasoline makes it to the injectors. A fuel filter itself is unlikely to leak, but the hoses that connect to it easily could.
Most fuel filters are located under the car in close proximity to the gas tank. They are often shielded by a protective cover and might not be visible if you take a peek underneath.
A leak in the fuel pump assembly could cause fuel vapors from the gas tank to escape. On some vehicles, the fuel pump is near the cabin. This means even a very small vapor leak will be detectable by your nose when you get in the car.
When the leak is coming from the fuel pump area, sometimes the whole assembly needs to be replaced. Other times, it’s just a simple o-ring or gasket that has worn out. The latter case is much cheaper, but it still may take a bit of labor to get to the fuel pump, depending on the model.
How to Detect a Fuel Leak
There are several ways you can detect leaking fuel. The best method to use may depend on the location and severity of the leak. The easiest way to detect a leak is of course to observe it spilling onto the ground, but rarely is the leak this obvious.
Fuel system pressure is also a factor to consider. Many of the fuel system lines are pressurized up to 60 PSI on port injected motors. High pressure fuel pumps used by direct injected motors can pressurize fuel up to 2,000 PSI!
Wear gloves and eye protection when working with any part of the fuel system. Consult a repair manual before disconnecting any fuel lines.
You may be able to use your nose to determine which part of the vehicle the leak is in (for instance, you only notice the gasoline smell when you pop the hood and the car is running). From there, you can perform a visual inspection on the fuel lines to see if any of the fuel system components appear to be wet.
You could purchase a leak detection dye and pour some of this into the fuel system. If you use a dye, be aware that it will take some time for the dyed fuel to make its way through the entire fuel system and into the component that is leaking.
Once you’ve given the dye enough time to propagate through the system, you can hold up a special light (usually a UV light, but this depends on the type of dye you’re using) and the dye will emit a bright color to help you find the exact source of the leak.
If this method fails to uncover the leak, there are special fuel and EVAP leak detection tools that either use smoke to detect EVAP leaks, or special technology to sniff out traces of gasoline and diesel. These tools can be pretty expensive, so you may want to bring your car to a mechanic to have these tests performed.
A fuel leak is no laughing matter and should be addressed as soon as possible. Not only does it hurt your fuel economy and cost you more at the gas pump, it could start a fire and endanger your safety and the safety of others.