Farmers will have to improve the housekeeping of their diesel stores after 1 January 2011 if they want to avoid the danger of blocked filters and expensive tank clean-ups.

That’s the date when so-called sulphur-free gas oil, which contains just 10 parts per million of sulphur, replaces current red diesel with its 1000ppm sulphur content.

The change has been timed to coincide with the introduction of new Tier IIIB engines to meet tougher emissions regulations. These engines have to run on lower-sulphur fuels to ensure that control systems will not be damaged.

It is not yet known whether fuel distributors will supply road-quality diesel that has been dyed red or a separate fuel (also dyed red) with a lower cetane level. Either way, fuel firms stress that the fuel will be more refined than the current red diesel and shouldn’t cause performance problems.

However suppliers of road diesel can add biofuels at up to 7% concentration which means the oxidation stability of the fuel will be poorer than that of current diesel. That means farmers will have to look after their fuel stores better, says the Agricultural Engineers Association.

Over time oxidation can precipitate solids that then block filters in vehicle fuel systems. To minimise the likelihood of this occurring, users are being advised to keep to a fuel turnover period of six months preferably and certainly no longer than once every 12 months.

That could be difficult in seasonal machines like combines and self-propelled foragers where fuel often sits for 11 months at a time. Draining down is one answer but increases the danger of moisture condensing in the tank.

Sulphur-free diesel containing biodiesel is also more prone to bacterial contamination than current gas oil. This can block fuel filters and, if contaminated fuel is used for a prolonged period, damage engines.

Bacterial growth can be prevented by eliminating water from fuel storage tanks and checking monthly that tanks remain free of water. If a bacterial growth outbreak has occurred, the tank may need emptying and cleaning or a specialist brought in use biocide additives and filtering.

Sulphur-free red diesel containing biodiesel is a better solvent than current diesel and may also pick up deposits already in fuel stores and tanks. To stop those deposits blocking filters, a one-off replacement of storage tank and vehicle fuel filters after 2-3 throughputs of sulphur-free gas oil is recommended.

Fuel seals in sight gauges on older fuel storage tanks may also be incompatible with sulphur-free gas oil, (irrespective of whether it contains biodiesel) and need replacing.

Farmers should examine sight gauges following the switchover to sulphur-free diesel, says the AEA. If there are signs of leakage you will need a one-off replacement of these seals.

Equally if you are having fuel storage tanks serviced in advance of the introduction of sulphur-free gas oil, it would be worth your while getting fuel seals replaced as a precaution.

Heating oil may continue to be supplied at 1000ppm sulphur (depending on the willingness of refiners and distributors to continue to supply it). So you will need separate storage for the two types of fuel and the two shouldn’t be mixed.

Modern engines could be adversely affected by anyone using the higher-sulphur fuel and vehicles equipped with Tier IIIB engines could suffer significant damage, says the AEA.

For more info, go to the DfT website