Diesel Fuel Adulteration

  • 09 Julie 2021
  • 5829
  •  Engen

It all makes its way inland via the pipeline or road transport and ends up in the tanks at your local filling station.   This begs the question, why then would some retailers sell diesel up to R2/litre cheaper than their competitors if the cost base is similar?  The answer may be that consumers are actually not buying diesel, but rather a mix of diesel, paraffin/jet fuel and some heavy furnace oils added in an attempt to alter the lab test results, and therefore the cost base is actually vastly different.

It would be wise for consumers to stick with brands they have come to trust and avoid the temptation of purchasing product at a price that is clearly abnormal versus the competition.

This technical explanation provides insights into the increasing phenomenon of diesel adulteration which all consumers should take heed of.

Prevent diesel adulteration: Save environment, save the life of your equipment

What is diesel Adulteration?
Adulteration is defined as the illegal or unauthorised introduction of foreign substance into diesel using kerosene (illuminating paraffin) or similar substance, with the result that the product does not conform to the requirements and specifications of the product. It does not only cause premature injector failures, but also increases emissions of harmful pollutants from vehicles, worsening urban air pollution that could cause adverse impact on health.

The foreign substances are also called adulterants, which, when introduced to a chemical substance, degrade the quality of the base transport fuel.

Adulteration of the fuel at the point of sale and during transportation has become an acute problem in the country. Transport fuels (gasoline and diesel) are often adulterated with other cheaper products, by-product or waste hydrocarbon. South Africa is using a marker to trace illuminating paraffin as a way of trying to curb this problem. With large numbers of adulterants available in the market, both indigenous and imported, the magnitude of the problem of fuel adulterations has grown into alarming proportions in the past few years.

Financial incentives arising from differential taxes are the primary cause of fuel adulteration. This act is prohibited in terms of section 37A(4)(a)(i) of the Customs and Excise Act 91 of 1964.

Consequences of automotive fuel adulteration to avoid tax, specifically Kerosene in diesel

Kerosene is the common adulterant utilised for mixing with diesel. As fuel prices rise, the public transport driver cuts costs by blending the cheaper hydrocarbon into highly taxed hydrocarbon.

Air pollution is the ultimate result due to high sulphur content (500 ppm maximum) of Illuminating Kerosene compared to diesel 50 ppm maximum. The use of high sulphur content product in a low sulphur content application inhibits the function of the catalytic converters, which act as an emission control device that converts toxic gases and pollutants into less-toxic pollutants.

Further, a fair proportion of diesel engine failures can be directly traced back to the quality of the fuel, which was in use. Fuel contamination, degradation or adulteration can have serious consequences in terms of blocked filters, stuck or worn injectors, as well as poor spray patterns and atomization.

Contravention of section 37A(4)(a)(i) is treated as a serious offence in terms of section 80(1)(o) of the Customs and Excise Act 91 of 1964. The person found guilty of this offence shall be liable to a fine not exceeding R20 000 or treble the value of the goods in respect of which such offence was committed, whichever is the greater, or imprisonment for a period not exceeding five years, or to both such fine and imprisonment.

The observations from tests and studies conducted suggest that a density test, is not a good indicator of diesel adulteration since the specification is wider, resulting in density being within the prescribed values even at higher adulteration.

The same observation applied to Kinematic viscosity and flash point. Therefore, this leaves us with only the IP Tracer test method that can be used to check or quantitatively measure the presence of Illuminating paraffin in diesel. This test can be measured qualitatively using the Authentix test kit, or alternatively be measured quantitatively through the laboratory environment. Important to note is that the latter is very expensive, due to the fact that only a few laboratories can perform the test in South Africa.


Adulteration of transport fuel, which is currently a flourishing business in our country, can lead to economic losses, increased emissions and deterioration of performance and parts of engines. Fuel adulterators are not just cheating consumers; the impure fuel is turning our cities into pollution hotspots, reducing engine efficiency, weakening national productivity and dragging the economy down.

For more information please call Engen Petroleum Technical Advisory Manager at 083 560 7285, alternatively, you can send an email to howard.nkohla@engenoil.com

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