Testing fuel filters: big differences

Ludwigsburg, 10th October 2023 – Global filtration expert MANN+HUMMEL has examined two gasoline fuel filters that have been in use for many years and have clearly been used in vehicles for longer than the specified service interval. Both are in-line fuel filters with metal housing – still with original seals: one is an OEM quality filter, the other is a low-quality variant. MANN+HUMMEL specialists assessed these filters in their test laboratory.

Quality filter protects the injection system and engine

Modern injection systems react sensitively to impurities in the fuel. Even microscopic particles can cause major damage. Global premium brand MANN-FILTER therefore offers fuel filters in original equipment quality with a high degree of filter fineness. They reliably protect all engines, preventing breakdowns and repairs – which are often expensive – for example to injectors and cylinders. The smallest particles in the range of a few micrometers are reliably separated. This is dirt that is barely visible to the naked eye. Dust from the Sahara is many times larger.

Fuel filtration depends on qualities such as high filter efficiency, stability and a long service life. However, in-line fuel filters available on the market vary greatly in terms of type and quality. From the outside, these "cans" generally look very similar. "Only a high-quality fuel filter optimally protects the sensitive injection system from abrasion. But from the outside, even experts find it hard to distinguish the performance of the filters. You can find the quality on the inside. For these kinds of situations, you can rely on MANN-FILTER," says Frank Bartel, Product Manager Fuel Filters at MANN-FILTER. Only a close look inside reveals more about the design, materials and functions of these top-quality filters.

Cutting the filters

Specialists first opened the aluminum housings of the two filters on a lathe to gain a view into the interior. For this purpose, the front cover was tapped off during machining and care was taken not to contaminate the filters with chips.

The OEM filter appears visibly loaded, recognizable by the dark color of the filter cellulose. The cover is spotlessly clean, and the O-ring remains soft and elastic even after many years of use. Jörg Schömmel, Senior Product Manager at MANN-FILTER, describes the ideal situation: "This is a high-quality filter. Both the consistently dark coloring of the cellulose and the clean side downstream of the filter element show that the filter has so far done a good job. However, it is not possible for the driver or the workshop to see when the filter needs to be changed, nor is it indicated anywhere. Anyone using a high-quality filter and regularly replacing it as specified by the vehicle manufacturer does not make any compromises, which could be costly, in protecting the engine and fuel system. For the inspected filter, the maintenance interval would have been four years, which was significantly exceeded. This could have led to higher fuel consumption, higher wear and a reduced service life of the engine and injection system, right up to total failure."

The quality, structure and quantity of the materials used are essential for a long service life. Special embossing of the filter media ensures an even and stable pleat distance and thus maximum filtration performance. This also avoids what is known as “packeting”, in which paper pleats fold into a block, reducing the usable filter surface area. Seals and sealing rings also play a major role: They are suitably sized and can withstand a wide range of temperatures and pressures. Ultimately, the pressure-resistant and high-quality material of the filter pots also ensures a high level of operational reliability over the long term. "After a long filter life, it’s clear that real OE quality can't be replaced by anything – except by renewed OE quality, as with a MANN-FILTER filter," Schömmel emphasizes.

Shocking results from the cheap filter

After removing the housing cover of the used low-quality filter, it became apparent that the front end plate had been massively deformed and the filter medium had collapsed. Bartel, on the discovery: "What we see here is, of course, the absolute worst case scenario – the filter medium made of cellulose has collapsed and has come away from the end plate, the fuel has been delivered unfiltered to the engine. You can also see in direct comparison to the OEM filter that the O-ring has completely hardened and thus no longer has any sealing function. The inside of the filter must contain only cleaned fuel, but this shows heavy contamination. The naked eye can observe uncontaminated areas on the filter medium, which makes me fear that this filter failed at an early stage. If the filter is functioning properly, the load must be evenly distributed, which means the entire filter medium is used for filtration."

Schömmel adds: "I had anticipated poorer materials and lower quality in the inferior filter before cutting – as we found in the O-ring, for example. The collapse of this filter once again underscores the risk posed by low-quality filters."