Case of the Month: Diesel Fuel Contamination

Jun 30, 2017 by

The insured bought a Dodge diesel pickup truck. He was the sixth owner. Three months and 691 miles later the engine would crank but not start. He had it towed to the dealer for service.

During the partial disassembly of the engine, the dealer’s mechanic identified a contaminant, such as “black sawdust”, in the fuel injection system. He cleaned what he could and removed and replaced the high-pressure fuel injection pump. He also recommended that the fuel tank be cleaned but this was declined by the insured. The engine was reassembled and the Dodge was test-driven. After about 15 miles into the test drive, the engine died and would not restart. The Dodge was towed back to the shop. The fuel tank was removed for examination and it was found that the inside of the fuel tank had been cleaned in the recent past.

GEI was then called and our expert inspected the Dodge at the dealer with the engine partially disassembled. He saw that the vehicle sustained a failure of the high-pressure fuel injection pump.

At the time of the inspection, the filter sock at the bottom of the lift pump assembly was partially clogged with debris. The main fuel filter had been recently replaced; however, the same contaminant was found at the bottom of the fuel filler housing.

The debris was the sludgy, slimy, acidic material that is sometimes called “diesel fuel algae”. The contaminant had been present in the fuel system for an extended period of time. Fuel samples that were pulled from the fuel tank and the main fuel filter housing were clean with no contamination visible.

It appeared that the fuel injection system was vandalized with the introduction of an unknown material and liquid, during the months prior to the insured’s purchase of the vehicle. It was apparent that the fuel tank had been cleaned, prior to purchase, in an attempt to either repair or hide the contamination damage. However, the prior cleaning of the fuel tank and the replacement of the high-pressure fuel pump by the shop were insufficient to completely clear all of the components of the fuel system. Due to the lack of proper repairs to the fuel system by the previous owner, the contamination had gravely affected the operation of the engine. No problems or service deficiencies were identified with the services performed by this dealer.

“Algae” is the term used to describe tank sludge and the jelly, slime, and other contaminants found in fuel filters. However, plant algae growing in an environment filled with water, such as a pond or an aquarium, is different from the sludge “growing” (or forming) in the fuel tank and that was observed on the fuel filter elements. While algae cannot live in an environment where there is no sunlight, there are several bacteria, fungi, and molds that grow in the oil/water interface between water and diesel fuel. They live in the small amounts of water commonly found in the bottom of fuel tanks and feed on the fuel. This is also a problem in aviation fuel. A few decades ago, sulfur in the diesel fuel would have killed most of the microbial growths, but due to smog issues, as much sulfur as possible is now removed from diesel fuel during the refining process.

Organic debris that clogs filters and injectors comes from two sources; 1) fuel breakdown products of fuel deterioration and re-polymerization (also referred to as polymer, tar, wax, or asphalt), and 2) the living and growing organic microbial bodies as well as their waste products.

When the fuel tank was cleaned, it wasn’t cleaned properly, and traces of bacteria and fungus were still living in the tank on the walls, baffles, and bottom. Once new diesel fuel was added, traces of water in the diesel fuel then provided an environment for microbial growth at the fuel-water interface. This caused filter-clogging sludge to develop, which would affect engine performance in as little as two weeks in a worst-case scenario (but longer for this Dodge).

In this case, the fuel tank was cleaned, but organic debris, rust, and algae contamination were found downstream in the fuel injection system. This indicated that the fuel tank had been partially cleaned, but the damage had already occurred to the fuel injectors prior to the purchase of the vehicle by the current owner.

There are specific procedures for cleaning a diesel fuel system for both physical and biological contaminants. If the fuel lines and injectors are already clogged or damaged they will need to be repaired or replaced before biological cleaning begins. Professional-grade biological cleaning procedures include several steps. First the biocide is added and flushed at specific concentrations to kill the microbial growths. Then it soaks for 48-72 hours for the chemical reactions to dissolve the sludge. Then the fuel goes through three filtration cycles of 25, 10, and 3 microns. Finally, the primary fuel filter cartridge in the primary fuel filter housing and the secondary (engine mounted) fuel filters are replaced.

In this case, the mechanical cleaning of only the fuel tank by the previous owner was a Band-Aid on an already damaged and contaminated fuel system.

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