Generators – Water in Fuel – Contamination

A diesel generator, as the name suggests, relies upon a clean supply of fuel to operate and to do so in an efficient manner. Any water in the fuel, will contaminate the engine.

The most common fuel used for this here in the UK is known as red diesel and may also be known by a variety of other names, such as generator diesel, tractor diesel and cherry juice. It is used widely in industry to power machinery and off-road vehicles. The red dye is added to prevent illegal use of this fuel in road vehicles, due to the much lower tax rate imposed on this fuel compared to standard diesel. Other European countries use blue dye for this same purpose.

Many generators are only used sporadically for standby power, and consequently the same fuel can sit in the tank for a long period of time if not years.

Fluctuations in the outside temperature can cause condensation to form in the tank, resulting in water entering the fuel.

Even fuel deliveries can be contaminated with water.


The fuel on he left has been filtered. The fuel on the right is the same age and is full of water

So what can go wrong?

1/ Check the generator has no roof canopy leaks – rain water

2/ Check the fuel tank has no roof leaks or rust patches

3/ Regularly dip your fuel tank and have an industry expert check for contaminates

4/ Listen for your generator ‘hunting’ when running

5/ Use a reputable diesel supplier

6/ Never use OLD or RE_USE discarded fuel in your generator

7/ Forget to filtrate your fuel tanks at least once a year

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