Watered down fuel – what exactly does it mean and what damage can it cause?


Low-quality oil and watered-down fuel (which means not meeting the standards) make a deadly combination for our engine. The engines manufactured by car companies become more efficient pretty much every year. Engineers keep working all the time on maximizing performance while keeping it fuel-efficient and complying with the ecological standards. As a result, drive units are subject to increasingly bigger strains, thus becoming more sensitive to oil and fuel quality.

When it comes to oil, most drivers are already pretty educated. Therefore, we change our oil regularly, using the brands recommended by the car’s manufacturer. The price might play a role, too. On the Internet, we can buy a few litter container of a a top brand oil for a little over 20 EUR. If we change our oil once a year, there’s no point looking to save a dozen or few EUR and put an oil of ambiguous quality in our engine. The financial benefits simply don’t make up for the risk of having our engine damaged. In case of fuel, though, things are unfortunately different.

First of all, at fuel consumption of around 10 litres per 100 km, when we buy fuel that costs 0,11 EUR less per litre, we save 11 EUR for every thousands of kilometres, which is quite a bit of money. The second thing is, very few of us realize how severe the consequences of using bad quality fuel are for our car. As a result, we are willing to visit cheaper gas stations risking getting watered down fuel in our tank. Thankfully, even at places like those, it is getting less and less likely to find fuel that doesn’t meet the standards, sadly it still does happen nevertheless. We know about it thanks to regular controls by the Consumer and Competition Protection Agency (CaCPA).

Watered down fuel, what exactly does it mean?

Every year, in search of stations that sell watered down fuel, CaCPA controls over 1000 establishments all around Europe. The number of gas stations where the inspectors detect watered down fuel fluctuates around 4 to 5% every year. In 2016 it was a little better in this regard, because sample tests only detected anomalies at a little over 3% of gas stations. Let’s take a look at selected parameters that are controlled by the inspectors.

Diesel parameters

• IT – ignition temperature – the minimum temperature diesel fuel has to be heat up to in order to create enough vapor that can combust in contact with flames. Although the ignition temperature being too low doesn’t have an impact on the engine, in extreme cases it can cause the diesel vapor to explode when filling the tank. According to a decree by the minister of economy, the minimum value of this parameter is 55 degrees

• Fraction composition – it defines heavy and light fraction content in diesel fuel. Too much of heavy fraction content causes a residue to be formed on the elements of engine. Not enough light fraction content, on the other hand, might cause trouble starting the engine during winter. Below we present selected values of respective parameters: 

– FC-250°C – fraction composition up to 250° C evaporates – this parameter shows us the amount of light hydrocarbons and is associated with startup properties of an engine. Should be maintained below 65%.  

– FC-350°C – fraction composition up to 350° C evaporates – this indicator shows us the maximum content of heavy fuel components – the minimum value of the parameter is 85% and it means that heavy components can’t make up more than 15% of fuel.  

– FC-95% – fraction composition 95% (V/V) distillates to temperature – the maximum value is 360° C.  

• S – sulfur content – too much of sulfur content in diesel fuel will cause various elements of the engine to corrode and wear down faster. Regulations say that the sulfur content can’t be higher than 10 mg/kg.

• FAME – FAME (Fatty Acid Methyl Esters) content – it’s a parameter that defines the allowed addition of biofuels in diesel fuel. It shouldn’t be higher than 7%.

• D – density at 15° C – wrong density of diesel fuel results in lowered power and increased fuel consumption. This parameter should be kept between 820 and 845 kg/m3.

• CN – cetane number – the cetane number being too low will lead to the engine making more noise and increased fuel consumption. The minimum cetane number is 51.

Gasoline parameters

• MON – motor octane number – it measures the fuel’s immunity to self-combustion, which might lead to a detonative combustion. It is harmful to the valves and pistons of the engine. MON is measured in a single-cylinder engine working at 900 revolutions per minute. The Europe standard for gasoline is 85.

• RON – research octane number – a measure analogous to MON, except it’s measured at 600 revolutions per minute. The Polish standard for gasoline is 95.

• Fraction composition (distillation) of gasoline – the indicators that together evaluate the fraction composition allow to determine whether after filling the tank with particular fuel we’ll be able to do things like starting the car normally during winter or if the fuel consumption will be too high or if the engine parts won’t wear down too fast. Here are selected values of different parameters:

– FC-70°C – fraction composition up to 70° C evaporates – this parameter characterizes start-up properties of gasoline and according to Polish standards it should be 20-48% during summer (05/01-09/30), 20-50% during the transitional period (03/01 to 04/30 and 10/01 to 10/31), 22-50% during winter (11/01 till the end of February).

– FC-100°C – fraction composition up to 100° C evaporates – this parameter informs us about the fuel’s average evaporation, which impacts stability of the engine’s workings – 46% to 71%.

– FC-150°C – fraction composition up to 150° C evaporates – this parameter shows the ability to evaporate heavy fractions, which impacts the wear of the engine’s elements. It should be at least 75%.

– FC-FBP – temperature at the end of distillation – exceeding this parameter will cause increased fuel consumption. It should be no higher than 210° C.

• S – sulphur content – too much of sulphur content in the gasoline units will lower the catalyst utilization time and disturb the workings of the fuel dosage control system and cause the engine to work badly. Like in diesel engines, it might also cause corrosion of certain drive unit elements. The sulphur content cannot exceed 10 mg/kg.

• VLI – vapor lock index – this indicator informs os on the fuel’s volatility, which is the light hydrocarbon content. The higher it is, the easier our car is to start. For the transitional period (03/01 to 04/30 and 10/01 to 10/31) it should be no higher than 1150.

• Oxygen content – too much of oxygen and its compounds in gasoline will lead to increased fuel consumption and bad functioning of the engine. It’s a result of the fuel-oxygen mix becoming too weak. The oxygen content in gasoline should not exceed 2,7%. It also applies to oxygen compounds such as isopropyl, tert-Butyl or isobutyl alcohol, as well as ethers with 5 or more carbon atoms and other organic compounds that contain oxygen. The permitted methanol content should not exceed 3%, with ethanol its 5%.

• VP – vapor pressure – the gasoline maintaining this parameter within a specified range provides a compromise between easy start-ups in low temperatures and avoiding vapor locks (which might cause the engine to suddenly stop!) during summertime. The value of the VP parameter during summer should be between 45 and 60 kPA, between 45 and 90 kPa during the transitional period and between 60 and 90 kPa during winter.

• DVPE Aroma – aromatic type hydrocarbon content – compounds of this kind have high octane numbers, but they have a negative impact on the tendency to create resin. Their level should not exceed 18% and 35% for the hydrocarbons of the olefine and aromatic type, respectively.

• Lead content – it should be no higher than 5 mg/l of gasoline. Exceeding this limit will cause disruptions in functioning of the engine resulting from the catalyst’s disfunction.

These are of course only some of the parameters checked by the CaCPA controllers. It’s better to remember, though, that failing to meet just one of the criteria is enough to say that this particular station sells watered down fuel, which means we should avoid getting our fuel there!

Watered down fuel – how to avoid it?

Sadly, there is no right answer to that question. We may run into watered down fuel at any gas station. What should raise our suspicions, though, is unnaturally low prices. It might have to do with bad quality of the fuel. We should also be up to date with the results of CaCPA controls. They publish a report every year which lists the names and addresses of gas stations where watered-down fuel was detected. This type of information is what media loves to spread around, so finding it should not be difficult. We should also carefully observe how our car works. If we can notice soon after filling the tank that the engine starts to choke, jerk or stop working, we should pull over and have it towed away to the mechanic in order to drain all the bad fuel.