After the gloom caused by the eventual loss of our use of red diesel I am sure that the government announcement that producers of up to 2500 litres of bio-fuel a year would effectively be duty free was a ray of hope. However this poses some important questions:

1. What does "produce" mean?
2. What is bio-fuel?
3. Will the engines run on it?
4. Will it affect reliability and long term maintenance costs?

Points 1 to 3 are easy, point 4 is far more difficult to answer.

1. Customs & Revenue’s phone service say "produce" almost means "use", but it cannot simply mean buying from a supplier who makes tens of thousand litres a year. Acquiring the raw product and processing it for your own use is probably a safer definition.
2. Bio-fuel is a fuel derived from a source that has recently lived, usually of vegetable origin, but perhaps from animal in the longer term. At present this means fuels derived from oil rich plants – the same oils that are used in foods. They come in three basic forms:

1. New vegetable oil like you get from the supermarket – any will do, but it is normally rape seed or soya oil.
2. Used vegetable oil from the likes of your local chippy.
3. Bio-diesel that has been chemically processed to meet a standard – EN 14214 which was derived from DIN51606. Looking at the production process, the chemicals used, the disposal of waste products and the vital need to chemically test each batch of base oil to calculate the quantities of chemicals required for each batch makes me question the likelihood of an amateur producer constantly meeting this standard.

From now on the term Bio-diesel refers to a fuel produced to EN-14214.

1. Will the engines run on it? Yes, but how well and for how long is open to question. The basic diesel engine will happily burn almost any liquid fuel that will ignite at around the 300 to 400 degree mark. Whatever you may read elsewhere there will almost certainly be a fuel consumption penalty. There is also a question over meeting the exhaust emission standards when running on anything other than the original test fuel EN 590 derv (road diesel).

This and subsequent statements DO NOT APPLY to modern automotive engines especially those employing Common Rail injection equipment.

2. Long term reliability and maintenance is where the problems lie and trying to give informed advice is very difficult. On one hand you have the bio-anoraks for who everything bio is absolutely problem free together with the commercial producers who are unlikely to admit to problems with their product. On the other a number of reports of problems plus most engine and injection equipment makers who seem to be ignoring the subject.

I am grateful to Isuzu for a number of documents, one of which is a signed declaration from directors of the major fuel injection equipment producers that indicates that their equipment must only be used for fuel that meets EN590 – that’s Derv – road diesel. However we know our engines run happily on BS2869 gas oil.

All the marinisers I spoke to referred me to the base engine maker apart from Beta, Isuzu and Russell Newbury. It is clear that there is a reluctance to publicly address the bio-fuel issue and in all cases the warrantee will be in danger if you use bio-fuel. Some would accept a 5% bio-diesel mixture but the reluctance of some of the base engine manufacturers’ to approve such a blend seems a bit odd when the government has stated that by 2010 they intend to "encourage" the use of such a mixture.

Once the warrantee period is over using bio-fuel is worthy of consideration, but as ANY bio-fuel requires processing in some form, often involving heating and mixing with chemicals, it can never be carbon neutral unless the chemicals, transport and electricity used at every stage of the process are obtained from carbon neutral sources. However it is far more carbon neutral than petro-diesel. It is also worth noting that the common form of bio-diesel produces more nitrogen oxides that ordinary diesel. These oxides are more environmentally damaging than CO²

Whilst reading the following sections please remember that the gaps between the working parts of the fuel injection system are incredibly small. They are measured in a few microns (one millionth of a metre or one thousandth of a millimetre).

The Welsh have ably demonstrated that diesel engines will run on this oil a few years ago, but there are some considerations.

The oil is probably as clean as the gas oil we normally use, so extra filtering may not be required.

The oil is more viscous (less runny) than gas oil so it will not get into the tiny gaps to lubricate the injection equipment as well as gas oil. It will also have more difficulty in passing through the engine’s fuel filters.

The injectors may not atomise the oil as finely as they will when using with petro-diesel leading to partial combustion, exhaust smoke, carbon build up inside the engine and gums forming on the cylinder walls and injector

There have been reports of rotary injector pumps being ruined, particularly the CAV DPx range – so hard luck for all those with BMC and older Perkins engines with DPA pumps. This appears to be related the "thicker" oil having problems getting into minuscule gaps.

Without additives (which may not work) the temperature at which solid particles start to form in the fuel (cloud point/waxing) is unacceptably high. This problem caused the Broads Authority to abandon trials on their patrol boats a number of years ago. I suggest you put some cooking oil in a fridge set to a low temperature and observe what happens.

The oil tends to oxidise easily. Have a look at the top of a part used cooking oil bottle that has been in use for a while. Think what that sticky "gunge" would do to the fuel system.

Some of the problems can be overcome. The viscosity can be reduced by either diluting with something like gas oil or diesel (beware of the duty implications of using things like white spirit) or using an electric fuel heater. Using a fuel heater may also involve manual or electrical valves to allow starting on gas oil, running on vegetable oil when warm and then purging the fuel system and stopping with gas oil in the system.

Machining grooves into parts of the injection equipment has been said to mitigate lubrication problems.

There are additives available that are said to overcome the cold weather problems.

Consider all of the above plus some extra problems.

If any animal products have been cooked in the oil the oil will contain animal fats that may make all the above problems worse. They may also form even more acids during combustion.

The oil will definitely require filtering and to do it to the tolerances required will almost certainly involve buying the filter, heating tank and the use of electricity.

Bosch and Delphi (CAV) are very definite that vegetable oil must not be used in their equipment.

There is another problem with vegetable oils and it has nothing to do with the engine. You have to be very strong willed not to keep eating with the constant smell of chip shops around the stern!

If you have an old engine that is close to needing replacement I can see little harm from putting a few litres of new vegetable oil into the tank together with residual gas oil in the late spring. However I would want to ensure subsequent gas oil fills had virtually diluted it away before September.

Some sources say that direct injection engines (no glowplugs) will have more problems with raw vegetable oil than indirect injection however I have problems with this view.

This is produced by mixing the oil with varying amounts of Sodium Hydroxide (a corrosive chemical) and Methanol. Methanol has a fire risk associated with it and both chemicals require protective clothing. After several hours of mixing, reaction and settling the bio-diesel is drawn off and washed and dried (to ensure none of the chemicals are still in it) and the residue is treated to remove the glycerine.

How well the result complies with EN 14214 must be open to question and you may well need to mix additives with it, especially in the winter to lower its waxing point.

An ongoing supply of chemicals and electricity are needed plus the cost of the processing equipment that will be in the low to mid hundreds of pounds. If you can make/scrounge most of the equipment, do not mind turning your garage into a chemical factory, have the time for processing and for collecting the used oil and can get the oil at no cost then I suspect making bio-diesel may be viable. However taking the equipment cost into account I have doubts. Also think about what will happen to the cost of used oil once the chippies realise there is a growing demand for it.

There are four main problems with using bio-diesel and they also apply to unprocessed vegetable oil to a degree:

1. It acts as a powerful solvent on the deposits that have built up in the boat’s diesel tank and fuel system releasing all sorts of "crud" into the fuel. The general advice is to use a 50% mixture for bio-diesel/gas oil for the first filling. Then pure bio-diesel and change to fuel filters. Carry spare filters and be prepared to change them if more sediment is released.
2. It attacks rubber so fuel hoses, seals and diaphragms may fail (I knew the old BSS leak off pipe rule made some sense!). Beta are testing the use of bio-diesel once the warrantee period has expired but emphasised that the fuel lift pump duties must be undertaken by an additional electric fuel pump in series with the mechanical one with rubber parts. Personally I would disconnect the mechanical pump, leaving it fitted to the engine, if I was going to do use bio-diesel long term.
3. It produces combustion products that react with the lubricating oil at higher temperatures forming a sort of gel so there is some question (in general) about oil change intervals. I feel that with our comparatively low intervals and the light engine loads associated with inland boating this is of far less concern to boaters than to road transport.
4. Some injectors do not atomise it well so some engines may be more satisfactory using a mixture of bio-diesel and gas oil. The larger droplets can cause smoke and cylinder wall/piston ring problems.
5. There is a question over how badly it deteriorates in longer-term storage and its reaction with water. Bosch states that it should not be used where it will be stored for longer than in a car in "normal use". Beta have bio-diesel that has been stored in a sealed plastic drum for 15 months without deterioration.
6. Our boats store it in vented tanks so the fact that it attracts and "dissolves" water into itself (it is hygroscopic) means that diesel bug may assume a greater significance and a biocide additive might be a sensible precaution.