5 Common Reasons for the Smell Of Gas Inside a Car
Do You Have a Gas Smell Inside Your Car?
"What causes the smell of gas inside a car?" is a question I hear almost every day. A gas leak might make sense as the most likely cause; but more often than not, the cause is unburnt gasses leaking from the engine or exhaust, in places where most people would never even think of looking. Here are five possibilities worth checking out.
1. The Oil Cap's O-Ring or Gasket
A very common place for a fume leak from the engine, which is very easy to overlook, the O-ring or gasket under the oil cap. I find this quite often and it's only a $5 repair. It's a very easy diagnosis, taking about 15 seconds, to determine if this could possibly be the source of your fuel smell. Here’s what to check;
- Open the hood and look at the area around the oil cap, if you notice oil and debris collecting on the valve cover just below the oil cap, most likely the o-ring is worn out and is leaking, causing fumes from the engine, which "smell like gas” to leak out and be drawn into the HVAC (Heating Ventilation Air Conditioning) fresh air intake located directly below the windshield.
- Inspect the o-ring for any damage or missing parts. If it looks flat, you may need to just replace it with a new one found at any local auto parts store.
- Check the oil cap for cracks, if you see any cracks, replace the entire oil cap. It may be a little difficult to get the right one because there are so many different sizes. If your local auto parts store doesn’t have one you could try the dealership or salvage yard.
Sometimes the solution for a problem is an easy fix, but it is often overlooked!
Leaking Oil Cap O-Rings
2. Loose Spark Plugs Can Cause a Gas Smell
How about them spark plugs? If the spark plugs are not tightened to the proper torque, the crush washer or sealing ring could be leaking fumes from the combustion chamber into the engine compartment right next to—you guessed it—the HVAC fresh air intake, drawing the fumes directly into your vehicles passengers cabin. Here’s what to check;
- First check to see if all the spark plug wires or coils are in good shape. Remove each one from the spark plugs one at a time, so you don’t mix up the order they are in.
- If all the spark plug wires and coils look OK, check the torque on the spark plugs. If you don’t have a torque wrench, try this method. Back out the spark plug a little so you can turn the plug by hand. Now tighten the spark plug until it bottoms out by hand. Use a ratchet and socket to tighten the spark plug a quarter turn or until it's snug. A quarter turn would be for example turning the ratchet handle from the 3 o’clock position to 6 o’clock.
- Check each spark plug one by one until you have tightened each one to the proper torque.
Loose or Broken Spark Plugs Can Allow Gas Fumes to Escape
3. Leaking Oil Can Also Cause A Gas Smell
What about oil leaks? Do you have used motor oil leaking out of the engine by an old gasket? Is it weeping down the side of the motor? Maybe it’s dripping onto the hot exhaust system? Used motor oil from inside the engine has unburnt fuel mixed into it, so if it’s leaking out of the motor and onto hot components, it could be the source of your fuel smell. What to check;
- Open the hood and use a flashlight to look for any dark oily wet spots on the engine.
- Valve cover gaskets are notorious for leaks. They sit at the top of the engine and absorb the most heat, which causes them to fail sooner then most gaskets. Also they sit right above the exhaust manifold which is the hottest section of the exhaust system. Inspect this area closely for any drips going down the back side of the engine.
- Look for any smoke coming off the engine when it’s hot. Smoke coming off a hot engine is a good sign there is an underlying oil leak that you cannot see. To find a small leak, you may need to bring the car to your local mechanic. Have them clean the oil off the engine and then add a fluorescent dye to the oil. This dye will glow green when a special UV flashlight is used to inspect the leak area.
Dripping Motor Oil On A Hot Exhaust Manifold
4. Exhaust Fumes With Unburnt Gas May Cause Your Smell
Exhaust leaks are another common fuel smell that gets drawn into the passengers compartment via the HVAC fresh air intake, especially if the exhaust leak is close to the engine and before the catalytic converter. An exhaust leak before the catalytic converter can have a pungent fuel smell, because the exhaust includes a lot of unburnt gasses before the converter cleans them out of the system on the way to the tail pipe.
- Listen for a louder-than-normal exhaust noise, if you accelerate and the engine sounds loud or different, you could have an exhaust leak.
- Listen for a ticking noise when accelerating. If the exhaust leak is close to the engine, the exhaust leak will make a loud ticking noise like someone tapping on a pie plate, if you hear this type of noise on acceleration, have your mechanic check your exhaust manifold for leaks.
- If you think you may have an exhaust leak but are not sure, try placing a doubled-up towel over the tailpipe and put your hand over the towel to stop the exhaust from exiting the tailpipe. If you don't feel the pressure building up at the towel, most likely you have a leak somewhere in the exhaust. If you have dual exhaust pipes, you may need an assistant to help block the other tail pipe at the same time.
Ticking Noise From An Exhaust Leak
Leaks In The Exhaust Can Smell Like A Gas Leak
Note: Some mufflers have vents at the bottom to allow moisture to drain; don't confuse this drain with an exhaust leak that needs fixing.
5. Is Your Oil Cap Missing?
How about a missing oil cap? If the oil cap is left off by accident, not only would the smell be unpleasant, but the fumes would be toxic and could literally kill you if the carbon monoxide levels got too high. And the mess a missing cap causes is very difficult to clean up without an engine degreaser. If you just had an oil change or someone just topped off your oil, and you smell gas inside your car, stop and check the oil cap, it could save you from a big mess. What to check:
- Open the hood and check to see if your oil cap is missing.
- If the cap is missing, look around for it in the engine area. Most of the time when someone removes the oil cap, they will set it down on top of the valve cover, and if they forget it, it often falls into the engine compartment. If the cap is gone, replace it. Don’t drive the car without it because that will sling oil all over the inside of the engine compartment.
Missing Oil Cap, Check The Engine Compartment
Gas smells don’t have to be complicated repairs; that’s why the problems mentioned here are overlooked so often. When a customer complains of a fuel smell, the first thing their mechanic will look for is a fuel leak. Or they may say, “You must be smelling the exhaust from the car in front of you.” If you smell fuel or gas while driving, check the items listed in this article, if everything looks OK, leave a question in the comment box below and I will get back to you.