If you’re paying attention, there are more and more European cars on the roads these days. And, if you’re doing repair and service on European vehicles, there’s a good chance you’ll see several Mercedes-Benz E-Class cars in your shop. Between the 2003 and 2009 model years, more than 300,000 E-Class models were sold.
They are great cars to service, but one issue we’ve seen is fuel odor/fuel leak complaints. We’re finding fuel leaks that may or may not turn on the check engine light.
The Vehicle Research and Test Center in East Liberty, OH, through the U.S. Department of Transportation at the request of the Office of Defects Investigation (ODI), published the results of a study, dated December 2014, concerning the Mercedes-Benz high-density polyethylene (plastic) fuel tank. Now if you’re an over-achiever, you’ll want to read the study. It’s available online; just search for Analysis of Fuel Tank Leaks on Model Years 2003-‘08, and click on the PDF (see NHTSA Excerpt sidebar for additional details).
The study was informative for several reasons. First, I realized the leak rate they checked for needed to exceed federal standards, so there are still small permissible leaks allowed. However, the vehicle owner should not be able to smell fuel.
The investigation started with the E55 AMG models that already had a recall for potential leaks. Remember, a recall is different than the extended warranty offer (I’ll talk about that later). The report noted that, on many models, the left-side sender and filter unit, which is a serviceable part, is required to be replaced every 60,000 miles. The high cost, $600 or more, results in many owners not performing this service. There is no word yet if this component is covered by the extended warranty.
The report mentions the difficulty in accurately determining the source of the leaks at several dealerships and a lack of clear work instruction to help discover the source of the leak or the cause of the fuel odor. I can relate as we’ve had this experience. When we saw an obvious leak at a sender unit, there was no reason to suspect the tanks would also be leaking, but this was the case more than once. This has led us to do a more thorough investigation of potential tank leaks when a car comes into our shop.
Mercedes-Benz Fuel Tank Leak Excerpt
All observed leaks by NHTSA were found to be at the top of the tank from the pump, filter or the fuel filling limiter valve located at the top center of the tank. These areas of leakage are located at the top of the fuel tank in unpressurized parts of the fuel system.
The fuel filling limiter valve is a caged float located inside the fuel tank with an external elbow that is connected to the vent system, including the charcoal canister. During refueling, as the fuel level rises and the tank fills, the float raises and seals the air vent. Fuel then backs up in the filler neck, and the fuel station nozzle shuts off.
The covered fuel tank components for the warranty extension include the fuel tank, fuel filter/sender, fuel pump and all related gaskets/seals and retention rings. The ODI is closing this investigation based on the manufacturer’s extended warranty of the affected fuel system components and in consideration that the nature of the leaks does not appear to present an unreasonable risk.
Fuel Tank Setup
The high-density polyethylene fuel tank is a sidesaddle design type with left and right connected compartments. There is a pass-through space on the underside of the tank, between the left and right compartments, for the exhaust and driveshaft to extend to the rear of the rear-wheel-drive vehicle. Each side of the tank has a fuel-level sender unit. The right (passenger’s side) sender is combined with an electric fuel pump. The left (driver’s side) sender unit includes a fuel filter, a tank-pressure sensor (for OBD II emissions checks upon startup) and a venturi-powered pickup to move fuel to the right-side saddle electric fuel pump.
Fuel Tank Diagnosis
The very first step you need to take is to look for service bulletins and open recalls. Start with www.safercar.gov — this is where you’ll see any open recalls or complaints that have been filed. You can search by VIN and will know if the recall has been performed. Mercedes-Benz recently extended the warranty to 15 years and unlimited mileage on many fuel system components, including the fuel tank and sending units, pumps, filters and seals on certain E-Class and CLS-Class cars.
Once you determine there are no open recalls, you should proceed to inspect the vehicle. Make sure you understand what’s covered and what’s needed.
Safety first, so never try to service any of the fuel tank components with more than a quarter tank of fuel. If you do, you’ll be paying for it later when you need to clean the fuel spill from the interior. Always use the correct tools and service procedures. It’s important to note that the only way fuel should be able to enter the passenger compartment is if the access covers are not installed correctly — so be sure they are!
After checking the basics like the fuel cap and fuel lines for obvious leaks or problems, you’ll want to pop off the lower rear seat cushion to gain access to the fuel pump sender unit cover plates. You can remove these to inspect the left- and right-side sending units for leaking. But, here’s the kicker: take a close look at the center mounting bolt of the plastic fuel tank ahead of the sending units. If you see signs of fuel staining on the tank, it may need to be replaced.
It’s very possible that you will need to replace both of the sending units as well, so be sure to carefully inspect them. Always follow all work instructions, use the correct tools and don’t take any shortcuts, like using a used fuel tank. We had a warranty company send one for replacement and it leaked, too.
Don’t be afraid to jump in, verify if the failed components are covered by the 15-year warranty extension and give your customers peace of mind. And, if a customer already performed this repair and paid for it, they can submit the repair invoice to the local dealership for reimbursement.
