What Are the Symptoms of Fuel Tank Vent Blockage?


You know when your car is sick. The problem is sometimes you don’t know what is causing the issues. One of the easiest things to diagnose, even for non-mechanics, is a blocked fuel tank vent. 

Fuel tank vent blocked symptoms are pretty recognizable. They are the same as a clogged fuel filter because both issues prevent fuel from getting to the engine. You will have poor performance, stalling, a hard time staring but will likely experience difficulty filling up your tank, or your car will either stall completely or won’t start at all.

Read on to understand how to deal with a clogged fuel tank vent and distinguish it from a clogged fuel filter. 

Understanding the Difference

The way to know which is giving you the problem is to check both. A fuel filter isn’t that hard to find or look at, depending on the make and model of your car.

It is found between your engine and your fuel tank and is either inside the fuel tank near the opening fuel line or it can be found in the fuel line, which is usually found at the bottom of your car. 

There could be a clog in the fuel line too. That is also pretty easy to figure out as you remove the fuel line and run a line through it to check for clogs. 

Then, there is the fuel tank vent. Understanding how to check it requires a little knowledge about this part of your car. 

Read: Why Car Won’t Start in the Cold?

What Is a Fuel Tank Vent?

The right combination of air to gas is important to your vehicle’s functioning. That means your fuel tank must be able to breathe. This is the purpose of the vent. The fuel tank vent relieves pressure and vacuum. 

Fuel is in a constant state of expansion and contracting depending on when it warms up and cools down. A long time ago, manufacturers used gas caps with vents to keep the right air, pressure, and vacuum but that proved ineffective because the fuel would spill out. 

A vent line is higher than the fuel filler neck or any other point on the tank. It can’t have a bend or dip because that is how condensation or fuel gets trapped. A trapped line will build pressure or vacuum in your tank and eventually that will purge the vent.

This results in tank damage as well as a gas smell coming through the line. Another common problem is that wasps sometimes build nests in the fuel vents. That can clog your vent line also.

Read: Why a Car Won’t Start in the Rain?

How Do You Check Your Fuel Tank Vent?

You have to be careful when checking your fuel tank vent so you don’t damage the tank or allow gas to get into the air. 

First, you find the air vent line and put a compressor into it. Shoot some air into it. A line that isn’t blocked will emit a gurgling sound. A blocked line will result in no sound. 

To further diagnose the problem, follow these steps. 

  1. Take the canister vent line off the gas tank and blow through it. You will know if there’s a blockage because it’s a short line.
  2. You can use compressed air to check it out. Many of them that come with a long plastic tubing to blow the air through will fix a clogging problem by blowing it out. You will find out quickly if it’s wasps causing the problems so protect yourself and be prepared with wasp spray, gloves, and other items.
  3. Try putting wire or plastic tubing through the vent to see if there are blockages.
  4. You will need to now drain the tank and let the inside air out. After it’s dry, reconnect the vent hose and fuel line and try another air blow with the compressed air. There shouldn’t be a blockage now.
  5. You can refill the tank if you solve the problem. 

Read: How Often Should The Fuel Filter Be Changed?


What causes too much pressure in a gas tank?

Any failure on part of the EVAP system will cause high pressure in the fuel tank. That means if something is clogged or not working. A common problem is a kink in the fuel vapor line or a clogged canister. 

There could also be a failed purge control or vent solenoid. 

Where is the fuel tank vent valve located?

Every car is different but the fuel tank vent valve is usually found underneath the car. It is typically close to the charcoal canister and is located near the fuel tank. 

Read: Bad Fuel Pressure Sensor Symptoms

What causes the fuel tank valve to fail?

The most common reason a fuel vent valve fails is because of corrosion. Being underneath the car, it is open to many things like dirt and temperatures which can lead to corrosion. It starts sticking either open or fails completely when it’s corroded.

Should gas vents be open or closed?

The gas vents should be open. Air needs to come into the tank to substitute for lost fuel volume. Without open vents, you will have negative pressure. That will result in backsucking fuel into the tank instead of it going to the engine. 

How much does it cost to replace a fuel vent valve?

It’s pretty cheap to replace a fuel vent valve as the part costs between $20 and $120, depending on your car. You will still need to pay the mechanic for replacing it and that can cost between $75 to $120. 

Why does my gas tank keep stopping?

The typical way pumping gas should work is the gas flows until the tank is full. That’s when the hole on the nozzle is covered by gasoline, indicating the tank is full. The nozzle has a vacuum and the switch for automatic shutoff is tripped. 

When there is a clog, particularly when the fuel vent is clogged, the turn-off happens earlier than when it’s full. This means you have a clog somewhere. 

How much does a fuel line repair cost?

The average cost of fuel hose replacement is usually between $120 and $500 but could cost more. This depends on the make and model of your vehicle and the prices charged by your mechanic. 

What is a fuel tank vent valve?

Vent valves are parts of the fuel tank that direct vapors that are generated. They are usually part of the carbon canisters and help protect the canisters from the fuel. 

Can you clean a fuel tank vent?

Yes, you can clean a fuel tank vent. You will need to take the canister off and blow air into them as well as wipe them down with a standard automotive cleaning product. Make sure the product you use is approved to be used around fuel areas. 

Where does the gas tank vent go?

The EVAP tube or vent line extends from the gas tank and usually is connected to the intake manifold.

Are fuel tank vent valves universal?

There are some universal fuel tank vent valves available on the market but most cars have a specialized part that is created specifically for that vehicle. It’s best to use a part meant for a specific vehicle then use a universal part.

What happens if a fuel tank isn’t vented?

Several terrible things can happen if a fuel tank isn’t vented. That includes the storage tank being under stress from vacuum or pressure with the fuel contracting and expanding inside the tank.

Read: Why Car Won’t Accelerate

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