Consequences of Bad Fuel and Fuel Defects: Insights from the Czech Trade Inspection

The Czech Trade Inspection recently published another list of fined gas stations, and a logical question was raised by the motoring community. What are the consequences of bad fuel? Will it hurt the engine? And do I even know him? We are looking for answers for all fuel defects that have been fined over the last year.

To begin with, one piece of good news: the quality of fuel in the Czech Republic is very good. Of the two and a half thousand samples that the Czech Trade Inspection (ČOI) took last year, 0.7 percent were objectionable.

The encouraging thing is that we therefore belong to the above average in Europe. Across the Union, the proportion of non-compliant samples exceeds one percent. This is a particularly comforting finding compared to the past, when controls in 2010, for example, secured almost eight percent of defective samples.

Now the news is bad. You almost never recognize low-quality fuel without chemical analyses. Some characteristics become apparent only after a longer period of time, and nothing specific can be inferred from the deteriorated engine operation. Reliable prevention is therefore only high-quality gas stations, which are most often the expensive, branded ones.

From October 2022 to October 2023, the inspection issued sixteen fines. Seven of them for too low a diesel flash point. The cause is dilution with gasoline, most often in the carrier’s tank.

In terms of volume, this is a small share, but technically it has a clear negative effect. The components of the injection system work with a pressure of up to 2000 atmospheres and their metal surfaces need lubrication. The so-called lubricity of diesel fuel is essential for the long-term service life of the high-pressure pump and injectors. And every drop of gasoline reduces it, because gasoline degreases.

Two fines were imposed for too high a distillation end for gasoline. It is the result of the opposite negligence during the transport of fuel, diesel has penetrated into it. It is denser, evaporates more slowly and at a higher temperature.

In practice, this has two serious effects. A part of the diesel that cannot evaporate and ignite is deposited on the cylinder walls, where it dilutes the oil and worsens the lubrication of the entire engine. The larger part is carried out by the exhaust gases into the exhaust and ignites violently on the surface of the catalyst, which can damage it.

Three fines were issued for gasoline vapor pressure being too high. This is most often so-called winter gasoline, which evaporates more easily, which improves startability at low temperatures. In summer, it evaporates very quickly. However, it can only be a problem for older engines with carburetors, which, as a result, start poorly when warm.

The other two transgressions related to the oxidation stability of diesel. In fact, it is not the instability of the mineral diesel itself, but the bio-component that is compulsorily added. In tanks, it is exposed to oxygen, which causes its degradation.

This defect can completely cripple the operability of the vehicle. Rapeseed oil esters after prolonged oxidation form a sticky slime that clogs the injection system. Injectors and the pump can be damaged, cleaning the system including the tank is laborious. According to the standard, diesel can be stored for three months. In the fined cases, the biological component was apparently already in an unstable phase.

The quality also fluctuated with LPG, where too high a sulfur content was measured in two cases. This must be the result of indiscipline directly during production. The mixture of propane and butane is partially created as a secondary product of the extraction and processing of natural gas, which contains sulfur and must be purified from it.

Sulfur clearly harms the engine. From the flue gas in the crankcase, it enters the oil, where it forms sulfuric acid with the precipitated water vapor. It accelerates the degradation of the oil and has a corrosive effect on the internals of the engine.

In one case, the fine was only confirmed after a two-year dispute. However, it was a dangerous defect when an inadmissible concentration of insoluble solid deposits was measured in the diesel. If dirt penetrates the delicate surfaces of the high-pressure injection system, it can quickly damage it.

Motorists from larger cities may be reassured by the sight of names and addresses penalized gas stations. They are almost always small, unbranded pumps in villages. It is still true that branded networks also offer higher quality assurance at a higher price.

Among other things, because, in addition to ČOI inspections, it pays for its own inspection system, the Seal of Quality. Laboratory tests here are provided by the SGS certification company.

Škarohlíd can point to the paradox that Globus in Brno received the highest fine this year – two million crowns – for oxidatively unstable diesel. That is, the one that makes mayonnaise if you don’t eat it in time. And Globus belongs to the Seal of Quality program.

But just as important as the discovery itself is what happened after it was announced. Globus stopped sales, cleaned the tanks and brought in compliant diesel. Which cannot be compared with private stations in the yards of agricultural enterprises, where winter gasoline is still sold in August.

2023-10-19 04:36:57
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