What is Fuel Polishing?

What is fuel polishing

Fuel polishing is the process of passing fuel through a filter system until the fuel meets a cleanliness standard that is fit for use your equipment. The desired cleanliness level is subjective, however there is an agreed industry standard stipulated by fuel system manufacturers. The standard is based on an ISO test labelled ISO 4406 and the desired cleanliness code is 18/16/13, read more about this here.  Only high quality fuel polishing systems will incorporate the following specifications of certified & tested filter efficiencies:

  • Removes ALL free standing water – SAE J1839
  • Separates ALL emulsified water – SAE J1488
  • Filters solid debris to a level of 10 microns or lower
  • ISO 4406:1999 Code 18/16/13 or better

Fuel is likely contaminated with water when delivered.

At the start of 2011 the EU introduced a 7% bio diesel mix into ALL diesels. Bio diesel holds onto water droplets and keeps water in suspension throughout the tank. Large particles of water will become too heavy for suspension and fall to the bottom.

Condensation in Fuel Tanks

Naturally occurring condensation is prevalent in warmer climates where the days are hot and the night’s cold. In the UK this problem occurs from Spring to Autumn.

Our fuel polishers are based around a technology called coalescence.

This means our fuel polishing systems actively remove emulsified water from diesel fuel. This is a critical function in any effective fuel polishing system. Modern diesel contains a 7-10% blend of bio oils. As previously mentioned bio oils naturally hold onto water as tiny droplets holding them in suspension in the oil. Consequently there are quantities of water in all the fuel. It is important to understand that this water does not drop to the bottom of the tank in the same way as if you poured water into fuel. Microbes attach to the water which serves as a habitat and then feed on the carbon molecules found in the diesel. This results in outbreaks of microbial growths known as diesel bug. These microbes are deadly and are the main cause of fuel system failures today.

Therefore it is VITAL TO SEPARATE WATER FROM DIESEL.


There are many different products on the internet but we recommend choosing a product that has credible certification of filtration efficiency. As explained above products that meet the stringent SAE test certificates are best, which ours do. Many products on the market have no certification at all leaving you guessing about how effective it is. You could say that buying these units are a gamble, but that is why they are prices so cheaply.


Other terminology to describe this process includes: fuel cleaning, fuel scrubbing, fuel polisher, fuel conditioning.

Fuel Polishing products that we offer