What is diesel fuel “algae”?

Written by Capt. Jeff Werner
Written by Captain Jeff Werner

Algae are a life form found in water, similar to algae growing in an aquarium. Algae do not live in fuel and it requires sunlight to grow. For years, people have been referring to tank sludge and the jelly, slime and other contaminants found in fuel filters as “algae”. The colloquialism “diesel fuel algae” is widely used and understood. However, there is no relationship between the “algae” growing in your aquarium and the sludge “growing” (forming) in your fuel tank and showing up on your filter elements.

There are three basic areas of concern about contaminants in fuel and oil:

  1. Water
  2. Inorganic debris (sand, dust, rust, etc.)
  3. Organic debris (fuel breakdown products and waste products of fuel deterioration and re-polymerization)

The organic debris represents more than 90% of all contaminants found in fuels and oil. It is this organic debris, the sludgy, slimy, acidic material that people refer to as “diesel fuel algae”. It could also be called a polymer, tar, wax or asphalt!

Capt. Jeff Werner, a Licensed USCG Master, has sailed professionally throughout the world.  He is also the Diesel Doctor, helping to keep your boat’s fuel clean and bright.

If you have additional questions for Capt. Jeff Werner, please email him [email protected].