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Gas Tank Fact Check: Answering The Most Common Questions

What to Know About Your Car’s Gas Tank

Today, we would like to provide some detailed information for customers to understand the depth of problems that our mechanics face when working on fuel systems.

Gas is highly volatile.

Those Hollywood explosions that you see on TV are typically produced when large volumes of gasoline are detonated. You can easily set your car on fire if you work on fuel system problems without proper training and tools. All it takes is a little spark or contact with hot surfaces for gasoline to ignite on your vehicle and spread like wildfire.


We, therefore, recommend that you do not attempt to carry out these repairs yourself and instead seek professional help.


Filling Up Car Gas at Gas Station

The Most Common Questions About Your Cars Gas Tank:

  • What Happens When Water Gets into Your Gas Tank?
  • What are the Symptoms of Bad Gas?
  • How do You Clean a Dirty Gas Tank?
  • What Should You Do if Your Gas Tank is Leaking?
  • Can You Drive a Car with a Gas Leak?
  • Why Would a Gas Tank Leak?



What Happens When Water Gets into Your Gas Tank?

It is NOT normal to get water in your gas tank.

Atmospheric moisture can condense in the gas tank if the car is sitting for long periods of time. There are fuel-saver formulas that are designed to protect cars dubbed “garage queens” that may spend a lot of time gathering dust. Adding these formulas to a tank of gas will help remove the moisture and prevent the gas from spoiling between driving months.

Bad gas mixed with water is more often the result of shopping for fuel at a cheap gas station with leaky underground tanks. In this case, the quality of the gas is noticeable when you experience running issues after a fill up at a particular station.

The problems with water in your gas tank are twofold.

The water is a corrosive oxidizing agent that can seize fuel pumps, engines, fuel injectors, and lead to the oxidation and deterioration of internal fuel system parts. The worst part of it is that you may not be able to quickly pinpoint which part has failed.

In the worst case scenario, the water may freeze in delicate injectors and damage them overnight. You may also suffer long-term intermittent problems from rust contamination that are impossible to solve without fully overhauling your fuel system.


What are the Symptoms of Bad Gas?

In some vehicles, the issues may be more pronounced than others. Any sign of subtle hesitation or rough idle may be attributable to bad gas. Some of the more objective symptoms are:

  • Rough Idle
  • Stalling
  • Hard-start Issues
  • An Illuminated Check Engine Light
  • Poor Fuel Economy
  • High Nitric Oxide Emissions
  • Engine Ping

The gasoline is lighter than the water and thus forces the water to the bottom of the tank. It is typical for a fuel pump to pick up from the bottom of the tank in a gravity fed system. If this were not the case, your fuel pump would run dry and seize whenever the tank runs low. The fuel pump needs fuel to cool and lubricate it during operation.


How do You Clean a Dirty Gas Tank?

Gas nozzle filling up gas tank

The easiest method is to buy a fuel system cleaner additive like Seafoam or Chevron Techron. Adding these detergents to the gasoline can dissolve the varnish and greasy residue that may accumulate in the tank over time.

If you run a high-octane gasoline, you will probably have less need to clean your fuel tank and injectors because the premium gas is usually blended with detergents. A higher octane fuel burns slower and is necessary for certain high-compression engine styles to achieve optimal combustion.

All engines can run on different octane ratings. The difference is how well they run.

High-octane fuels reduce the knock that occurs at higher RPMs in high-compression engines. Knock is an explosive shuttering of the pistons from premature combustion. If you put higher octane fuel in a vehicle that requires 87, you will usually notice an initial boost in performance thanks to the detergents freeing up the injectors. Long-term performance will diminish due to the irregular fuel-mapping that higher octane fuels require your vehicle’s onboard engine management computers to calculate.

If your gas tank is really dirty or the vehicle is pretty old, you can manually clean it. In this case, you will have to remove the fuel tank from the vehicle. Shops typically have equipment to pump or siphon the gas out of the tank before removal. A full gas tank is quite ponderous and difficult to work with unless you first remove the fuel. Every vehicle is going to be different in coordinating the removal.

There are usually some fuel lines running to a twist on cap that provides access to the fuel pump for ease of replacement. You should first loosen the gas filler cap on the outside of the vehicle before beginning repairs on any model to depressurize the system. After you remove the fuel pump assembly and lines from the tank, it is probably just a matter of lowering the tank onto a transmission jack after loosening some straps and bolts holding it in place. The fuel filler tube will need to be dislodged as well. Most modern gas tanks are plastic and easier to replace and work around while also being less likely to require manual cleaning.

Cleaning the gas tank is then a matter of draining out any excess gasoline and using a powerful shop light to inspect the interior and exterior for rust or damage. You may want to use a manual degreaser or simply powerwash the interior clean. If there is a lot of rust, you may want to consider replacing it with aftermarket made-to-fit parts or retrofitting a universal tank style into place on older classic cars. You may want to stop in your local auto store or a classic car restoration shop to see if they can order a custom fit part even if the original equipment has been discontinued at the dealership. Many of these shops boast of having access to a global network and the ability to purchase any part ever made.

Always replace the fuel filter when you are doing any type of fuel system repairs. They are inexpensive and easy to install. Replacement can save you major headaches in troubleshooting a system after repairs. You can check everything else in the fuel system and replace it with no success if the fuel filter is clogged. Running fuel injection cleaner, for example, can deteriorate aging fuel filters or unlodge gunk that was built up in the gas tank. A clogged or deteriorating fuel filter will cause a no-start issue that can make you scratch your head.


What Should You Do if Your Gas Tank is Leaking?

There are various patch kits on the market for both metal and plastic tanks. The most effective method of repairing your tank would be a total removal and replacement. If the tank is metal, you may be able to have it welded by a professional after you remove it. The plastic tanks use an epoxy kit that can work if applied properly.


Can You Drive a Car with a Gas Leak?

It is very dangerous to drive a vehicle that is leaking gas. Whether it is from a fuel line or a leaky gas tank, it would not take more than a simple spark or hot surface to ignite the veritable fuse dripping for you underbody. The logical result would be a bonfire. Furthermore, if your vehicle is leaking a little gas overnight when sitting, it is probably shooting out when the tank is pumping at high pressures. In either of these cases, all it takes is a hot exhaust part to ignite the dripping fuel and send your vehicle up in smoke.


Why Would a Gas Tank Leak?

Gas tanks can be defective and may start to come apart at the seams. They can be damaged from road debris or simply rust out over time. If there is excess vibration because the tank is not mounted securely, this may also damage the tank by friction wear over time. It is possible for some solvents to even deteriorate a plastic tank if they are not safe to use for plastic tank fuel systems.


Reasons to Consider Having the Service Done by Professionals

There are many reasons why you may encounter a fuel leak in your vehicle or want to clean your gas tank. Always be sure to disconnect the negative lead from your battery to prevent shorted wires from sparking and causing a tragic fire. Gas tank replacement and repairs are extremely situational and brand-specific. It is impossible to outline the steps for your particular vehicle in any greater detail. A gas tank leak doesn’t have to mean you need to lay down money for a new vehicle. It is not the end of the world.

A professional shop can typically replace or clean your gas tank for under $200 to $600 in labor. You will likely have to spend the equivalent for the equipment to do it yourself properly. When you take your leaky tank to a professional, you have peace of mind that the job will be done right, on budget and on time. Having decades of experience and a shop full of master mechanics who have seen it all and done it all helps you relax. You don’t want to do these repairs if you are an amateur mechanic with a socket set who has to keep checking for leaks every so often to ensure it was done correctly.

This isn’t a novice level job that you can complete without unnecessary aggravation and stress.

Fuel system problems are also quite complex if the leak is not the only issue. If it is not from obvious road debris damage or rust, why did the leak form in the first place? After repairing the leak, a professional mechanic will have tools on hand to test the line pressure and to ensure the injectors are pulsing. They will typically start any fuel system pressure repair by replacing the fuel filter if it has not been serviced in a while. If the line pressure is low and the fuel filter is good, the next step is to check for other pressure leaks. The final step is to check the connections to the fuel pump and possibly remove it for a visual inspection and replacement.

Checking the electrical components of the fuel system opens up another dimension. If there is suddenly no pressure at all, the first step is to check the electrical systems.

A professional shop will have the wiring diagrams on hand and years of experience to understand what all is connected to this circuit. In some vehicles, there is something called an inertia switch that will cut off the power when the vehicle is in an accident to automatically disable the fuel system and prevent fires. It is possible for this switch to malfunction or to cut off fuel without an accident. Most vehicles have both a fuse and fuse pump relay that will need to be checked before major repairs are considered.

Computer diagnostics open up an even deeper dimension. If there are any trouble codes on the engine or drivetrain management computers, this is likely related to the fuel problem. These engine codes can be vague and misleading. Only an expert with years of experience and factory repair resources on hand can ensure that the codes are not intrinsically related to the problem.

Many vehicles will register misleading engine codes when there is a no-start issue regarding the cam position sensor and other devices. These generic codes rarely have anything to do with the failure itself.


Why Do You Need A Professional Mechanic?

The increasing complexity of automotive repairs and special tools necessary to complete the job, require the trusted care of professionals in most cases. The most dangerous thing one can encounter on any vehicle is a fuel leak. The fact that fuel leaks are often situated near hot exhaust parts creates an immediate safety hazard and an eventual fire. Don’t risk your entire investment by practicing on your fuel system. You will likely end up replacing every part in the fuel system before the issue is solved, that is if you don’t light it up like a book of matches first.

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