Fuel Tank Vent Blocked Symptoms – 5 Things To Check

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

Fuel tank vent blocked symptoms 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. 

Fuel tank vent blocked symptoms

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

Car fuel system diagram

You’ll find it at some point between your engine and your fuel tank. It’s either located inside the fuel tank near the opening fuel line, or else in the fuel line itself, which usually runs along the frame under your car. 

If the filter is fine, there could be a clog in the fuel line, instead. That is also fairly easy to figure out by disconnecting the fuel line and running a flexible rod or wire through it to check for clogs. 

And then there is the fuel tank vent, which also can possibly have a blockage. 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 tank vent diagram

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 any bends or dips, as they would end up trapping condensation or fuel. 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. An unblocked 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 arm yourself 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?

FAQs

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 indicates that something has become clogged or is 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 can usually be located underneath the car. It is typically close to the charcoal canister and is located near the fuel tank. 

Fuel system components

Read: Bad Fuel Pressure Sensor Symptoms

What is a fuel tank vent valve?

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

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. A corroded vent valve starts sticking either open, or rather it fails completely.

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. 

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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 back-sucking fuel into the tank instead of it going to the engine. 

Why does the gas pump keep cutting off before it’s full?

The typical way pumping gas should work is the gas flows until the tank is full. The cut-off point is triggered 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 cut-off happens earlier than when it’s full. This indicates you have a clog in the vent 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. 

Can you clean a fuel tank vent?

dirty 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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