The top reasons why your car can sometimes smell of gas include gas leaking from a fuel line or fuel filter, an engine that is running rich, a leaking gas tank or gas fumes may just be coming in from the air outside.
No matter what the cause, you should definitely check it out as soon as possible as a fuel leak and the smell of gas in a vehicle can be dangerous.
There are some simple checks that you can carry out yourself to narrow down the cause, and others that you may need a mechanic to check out, with specialist equipment.
5 Reasons Why Your Car Smells Like Gas
It's fairly common to get a smell of petrol or diesel just after you fill up your car. But if that smell lingers longer than it should, or is there all of the time, it could be a sign of a fuel leak.
Here are a few common reasons why your car can smell of gas:
1. Fuel leaking from the fuel delivery system
The fuel system in your car is a sealed, pressurised system. The most common places that you can get a leak are at joints in the system.
An example of common leak points are where the fuel lines connect to the fuel filter, at the fuel distribution rail (that feeds the injectors) and at the injectors themselves.
Because the fuel system is under pressure, a leak can cause fuel fumes to escape even if there is no sign of liquid fuel getting out. You may also notice that it's a bit more difficult to start the car, especially after it has been sitting unused over night. This is because a leak will cause a drop in fuel pressure when the engine isn't running, causing fuel in the system to flow back towards the fuel filter.
2. A cracked fuel tank
Most fuel tanks these days are made from a hard wearing polycarbonate material. It's unlikely that a modern fuel tank will crack or leak by just getting old, as they don't rust.
Most fuel tanks are mounted on the outside of the vehicle (near the back wheels). As such, they can be exposed to things like loose road debris, raised speed bumps and high kerbs. Fuel tanks are robust, but can get punctured or dinged and this can lead to small leaks, that over time can get worse.
When it comes to older fuel tanks that are made from metal such as steel, it's inevitable that they will eventually rust. This can be caused by stone chips from the road that chip away at the paint or water collecting around the brackets or straps that hold the tank in place.
If you suspect the fuel tank is leaking, even slightly, get it checked out straight away. This will involve draining the fuel system and removing the fuel tank so that it can be pressure tested for leaks, and is usually best left to an expert.
The best way to fix a leaking fuel tank is to replace it. Sometimes older fuel tanks can be repaired or 'patched', but this is usually only carried out if the car is a classic or a replacement tank is too difficult to source.
3. Your car is old (and does not use fuel injection)
Older vehicles did not use direct injection for supplying fuel to the engine. Instead, they use a carburetor to get the right fuel air mix into the engine.
The fuel system in engines that use carburetors, do not work under the same fuel pressure as a direct injection engine. The fuel and air actually mix in the carburetor before it goes into the engine cylinder, unlike a direct injection system where the fuel is pumped directly into the engine cylinder, under pressure.
Because of this difference, fuel residue can sometimes hang around the carburetor after the engine is shut off, and this can cause a gas smell under the hood and sometimes inside the car. It's not really a problem and it can be a 'feature' of older, classic cars.
Sometimes the carburetor is faulty or is leaking fuel and this can be the cause of the smell. So it's always a good idea to find the source of the leak and fix it if necessary.
4. Your engine is running rich
If your engine is not running properly it could be caused by a fuel/air mix imbalance. Sometimes too much fuel is added to the mix, causing the engine to run rich.
Extra fuel that is not burned can find its way to the exhaust and you may be able to smell it in the exhaust fumes. This is something you should get checked out sooner rather than later as it could be a sign of something badly wrong with your engine. It can also wreck a catalytic converter if not fixed promptly.
5. Your pollen filter (cabin filter) needs to be changed
Sometimes the smell of fuel in your car can be coming from other vehicles on the road.
If you drive a fairly modern vehicle with air conditioning, then it should have a cabin filter (sometimes called pollen filter) fitted. This is fitted between the outside air intake and the cabin. Its job is to filter out impurities from the air.
On some vehicles the pollen filter is coated with what's called 'activated carbon'. This will help to absorb extra chemicals from the air and should block noxious gas and exhaust fumes.
The cabin air filter should be changed every 6000-10000 miles. If you do a lot of city driving it could need changing at shorter intervals.
How To Diagnose A Car That Smells Like Gas
1. Check the engine bay for fuel leaks
This may be easier said than done on a newer vehicle. Most new engines have lots of plastic covers that can make it difficult to inspect engine components.
If you can, try to inspect the top of the injectors for fuel residue. Follow the fuel lines as far back as you can to the underneath of the engine. If possible, remove the covers from under the engine and along the car to the fuel tank. Check for a build up of fuel residue or for drops of fuel.
2. Check the fuel tank for leaks
Check underneath the rear of the car for the fuel tank location. It can be difficult to check the entire tank as it is usually partially hidden by other components such as suspension parts or driveshafts.
If it's an older vehicle, try to assess the overall condition of the fuel tank. If it looks rusty or damaged you will probably need to have it removed to fully test its condition.
3. Check the condition of the cabin filter
It's easy to visually check the condition of the cabin filter. Check the location of the cabin filter in your vehicle manual. It's often located under the dashboard inside the vehicle. If not, it may be located under the hood near the windscreen. You may need a screwdriver or small socket wrench to remove the plastic cover that holds the cabin filter in place. Take care pulling out the cabin filter, noting the direction it needs to go when refitting.
If the cabin filter is very dirty and dark in color then it needs to be changed. New pollen filters are not expensive and are easy to fit. You should always try and fit a high-efficiency cabin air (HECA) filter as these have been shown to reduce the amount of pollutants entering a vehicle by up to 93%.
4. Run an engine diagnostic to check for faulty sensors
Sometimes a gas smell in your vehicle can be caused by a problem with the engine. The best way to check for an engine fault, is to run a diagnostic that will check for any errors that may be stored in the ECU.
5. Keep an eye on fuel economy
If the engine is not running as efficiently as it should, then you'll definitely notice a drop in fuel economy. This is usually down to the ECU trying to compensate for an out of range value that it's receiving from one or more sensors.
If a sensor is sending a reading back to the ECU that is outside a pre-configured range, then it will default to a pre-programmed value to help keep the engine running. Sometimes when this happens you will see the check engine light on the dashboard telling you that something is not right with your engine.
The car may also enter 'limp home mode' to prevent any damage being done. If either of these conditions occur you should always get the engine checked out as soon as possible.