Mercedes C-Class Fuel Tank Problems (Solved & Explained!)

The Mercedes-Benz C-Class is among the brand’s most popular executive sedans.

It is sought after not only for its great looks and the prestige of the Mercedes brand but also for its powerful engine options.

Despite these positive attributes, however, there are some common issues with the Mercedes-Benz C-Class, one of which relates to the fuel tank.

This article explains the “Mercedes C-Class Fuel Tank Problems”…

What Are The Causes Of Fuel Tank Problems?

If you are experiencing problems with the fuel tank on your Mercedes-Benz C-Class, then there could be several causes behind it.

One common problem area is the inside pipes of the fuel tank not working properly. Another common issue relates to the fuel filter and pump.

If the filter is clogged or the fuel pump damaged, then fuel could be contaminated and/or not getting where it needs to be in enough quantities.

All of these things can be checked and tested, and are typically not so complicated to repair.

Inside Pipes Not Working

The inside pipes of the fuel tank, also known as the fuel lines, are located throughout your fuel system.

They also connect your fuel tank to the engine and also to the filler cap where the driver pumps gasoline into the tank.

These interconnected inside pipes have to be kept clean, clear, and functioning to ensure that enough fuel makes it to where it needs to go.

Over time, carbon, debris, and other contaminants can build up in the fuel lines and cause blockages. These can even be caused by imperfections in the gasoline itself.

Therefore, if you have been putting cheaper gasoline into your Mercedes-Benz over a long period of time, then that may have contributed to your current problem with the pipes getting clogged.

If you find that your C-Class is struggling to start up and/or is suffering from misfires and poor engine performance all around, including frequent stalling, then problems in these pipes are a likely explanation.

Flushing the fuel lines in a Mercedes-Benz C-Class will likely cost at least $80 to do, but it could go up to $100 if the clogs are more severe.

Clogged Fuel Filter

Just as your oil filter and air filter protect your engine from the many impurities and contaminants that can build up, the fuel filter does the same thing for your gasoline.

Even high-end Mercedes-Benz cars use fuel that has impurities within them.

The filter screens the dirt and rust that can build up inside the fuel tank and prevents it from traveling down the fuel lines to your engine where it can cause more damage.

You can know if your fuel filter is experiencing problems first with a visual inspection, but also from the car’s performance.

When the fuel filter is clogged, you will certainly notice an increase in sputtering, as well as uneven acceleration.

Like other filters, your fuel filter has a limited life. It will typically be able to do its job for two years, but that lifespan could be shortened if you drive a lot.

The key to solving a clogged fuel filter is to simply replace it, a task that should cost about $140 on average for a Mercedes-Benz C-Class.

Damaged Fuel Pump

The fuel pump’s main job is to send gasoline from the fuel tank through the pipes and filter to the engine where it can be combusted and propel your Mercedes C-Class forward.

The pump specifically sends fuel to the injectors, which then pushes the fuel into each cylinder for combustion.

If the pump is damaged, then the inevitable result is not enough fuel reaching the injectors and thus not enough combustion happening to propel the car forwards.

The signs of a failing fuel pump include a loss of power when the vehicle is under any stress, massively reduced gas mileage, an engine failing to start, but most obviously will be a fall in fuel pressure indicated by the fuel pressure gauge.

Let’s say we take the gauge reading as the first sign, the next step would be to test the fuel pump (see below).

If after testing you discover that the fuel pump needs replacing, then it would typically cost about $325 for the parts plus another $150 or so for labor costs.

That brings the job to quite a steep $475 to replace the fuel pump.

How Do You Test The Fuel Pump?

Before you engage a Mercedes technician to replace the fuel pump, however, you’ll want to test it to make sure that your initial gauge readings are accurate.

You can do this using a simple fuel injection pump tester from a brand like U.S. General.

The kit itself sells for under $30 and is widely available online and from automotive supply stores.

On most new cars, you can simply pop the hood of your C-Class and look for the Schrader valve to attach your kit to, and then check the reading on the gauge in psi.

If it appears to line up with what your dash gauge said, then you will know that the fuel pump is the problem and it either needs repairing or replacing.

If the C-Class is older and there’s no Schrader valve, then you’ll have to use the additional attachments in the injection pump tester to connect it right to the fuel filter and get a reading from there.

This can get both messy and complex, however, so you might want to leave this to a mechanic.

Air In The Fuel Tank

As a general rule, you don’t want to get unwanted air into any part of your fuel system. This includes both the fuel tank and the fuel lines.

Air can build up in your gas tank as a result of gasoline evaporation creating vapor pressure in the air above the fuel you store in the gas tank.

Air can also get into your fuel lines via pinhole leaks in the low-pressure lines that connect the tank and fuel pump.

This also brings unwanted air into the system that ultimately causes a reduction in performance.

Bleeding The Fuel System

Bleeding the fuel system needs to be done as a way to remove air from the system but also whenever you replace the fuel filter.

After replacing the filter, you or a mechanic has to attach a tool known as an external hand primer.

This is connected up between the tank and the filter and features a spherical rubber hand pump which you squeeze in a steady rhythm until you feel the fuel coming up the pipe.

You then remove the primer and replace the fuel hoses correctly.

Most Mercedes-Benz engines require this method to be used. If your engine has a mechanical-lift fuel pump fitted, then you can also use that to directly pump fuel without turning on the engine.

These procedures involving fuel are nearly always best left to the professionals.

Bleeding the fuel system will typically cost you around $80-100 because it will rarely be done as a stand-alone procedure.

It will typically be done as part of a more comprehensive fuel system checking and cleaning.

Low Fuel Pressure

While some people claim low fuel pressure in a car isn’t such a serious problem, they are in fact wrong.

Having low fuel pressure – as indicated by your fuel gauge – can cause rough idling, hard starting, stalling, and can even cause damage to your catalytic converter, which is one of the most expensive single components to either repair or replace on a Mercedes-Benz and just about every other car.

Low fuel pressure can be caused by many things, including dirty or clogged fuel filters, a weak or damaged fuel pump, problems with tank venting, or clogged fuel lines.

You can determine if you have it by regarding your car’s fuel pressure gauge, but also conducting a pressure test as we described further above.

Fuel Gauge With Wrong Information

It is possible that the information on your fuel tank gauge is incorrect. This is most likely due to a bad fuel sending unit.

This unit measures the amount of fuel currently sitting in your gas tank and then sends that information to the fuel gauge that you see on your dashboard.

That’s how you know if your C-class is empty or full.

You can self-diagnose fuel gauge issues by first turning the ignition on and off in your C-class and carefully observing whether or not the needle on the gauge moves.

A faulty gauge will frequently be stuck in one place (often on “Empty” or “Full”), or alternatively will behave erratically quickly shifting from one point to another.

Your fuel sending unit is not a component that is regularly checked as part of your vehicle’s service, so it’s best that you keep an eye out for problems with the gauge.

Having the fuel level sensor and sending unit replaced can cost up to $170 if you have a professional Mercedes-qualified technician do the job on your C-Class.

How To Reset The Fuel Gauge?

Another way to solve the problem of a faulty fuel gauge is to manually reset it. This can be done on your Mercedes-Benz C-Class in a number of steps.

The first thing to do is turn the car off, and then you have to remove the fuse cover located below the passenger side door.

You should see the 15-amp blue fuse number F5 once the cover is taken off.

You pull that fuse first to check it out. If the fuse looks alright, you can put it back and restart the car. This has reset your fuel gauge.

If the fuse appears blown or otherwise damaged, then you’ll have to replace it with a new one, but the resetting will remain the same.

In What Case Do I Have To Change The Entire Fuel Tank?

Having to replace the entire fuel tank in your C-Class is thankfully not a common scenario, but there are times when you may need to do it.

If the fuel tank is dented, for example, then its structural integrity is compromised and it becomes more likely that dangerous leaks can develop.

The same is true with the presence of serious rust, cracks, and other physical damage.

Most drivers will sincerely hope that they don’t have to have their tank replaced because a professional replacement of a Mercedes-Benz C-Class fuel tank can range from $1,950 and $2,200.

That cost is inclusive of labor costs.

That’s an expensive item of repair, but if the tank is damaged in any way, then it becomes an essential need.