What Car? Q&A - Can I use biodiesel?

Q: Can you tell me why biodiesel is not recommended for my Astra? I know that my owner’s manual advises not to use it, but by contrast, my wife has been told by VW that her Golf can use biodiesel because it was made after 1996. I would like to know why.
Ian Douglas

A: Biodiesel is an alternative fuel made from the natural oils of organic matter, such as vegetables, seeds and beans. The main benefit is that it’s produced from renewable resources which are biodegradable, non-toxic, and naturally free from sulphur.

However, biodiesel is more expensive to produce than conventional diesel, which is why it isn’t in wider use. One of its main drawbacks is that it starts to solidify at zero degrees centigrade, which limits its use in countries with cold climates.

Biodiesel’s properties are similar to those of normal diesel, so it can be used in existing diesel engines with modifications, and can replace it in most applications. It is most often used as an additive to normal diesel, improving lubrication and lowering the sulphur content.

However, blends of over 5% biodiesel do not meet the British Standard specification for diesel (BSEN590) and are usually not supported by most car manufacturers.

Some European manufacturers have modified their diesel engines to allow them to run on biodiesel, but many have not. There is a shift towards making engines compatible, and this generally only involves the use of appropriate synthetic rubbers for seals, fuel hoses and gaskets.

Until 2004, the Volkswagen Group approved its diesel engines to run on biodiesel, but it has now changed its policy over concerns about the sensitivity of the latest-generation of fuel injection systems, and the quality of the biodiesel fuels available. It now only warrants its diesel engines for a 5% blend.

Owners of older VW Group diesels may find their cars can run on biodiesel – but must call their customer services department and quote an engine code to check.

Vauxhall does not recommend using pure biodiesel without modifications to the standard engine, and using such fuels will invalidate any warranty.