London, November 8:

In an effort to get round the big rise in oil prices, thousands of motorists have taken to running their cars on supermarket-bought vegetable oil and it’s all perfectly legal.

Last week in the UK, the average price of a litre of diesel went though the £1 barrier again, prompting many drivers of older diesel cars to consider using shop-bought vegetable oil in its place.

Plenty of owners of cars with older diesel engines can run their car on vegetable oil — either mixed in with ordinary diesel or, following some modifications, entirely on such oils. Users point out that Rudolf Diesel originally designed his engines to run on peanut oil. The only downside is the smell that comes out of the exhaust, which has been likened to a barbecue.

The use of this ‘alternative’ fuel was given a big boost in Britain recently when the UK treasury relaxed the rules on the taxation of home-made and shop-bought oil. Since

June, drivers have no longer been required to pay the fuel duty. Anyone can now use up to 2,500 litres of vegetable oil a year for personal use without having to pay any extra tax.

The move has led to a huge new demand for vegetable oil as thousands of motorists started using it, attracted by the possibility of big savings. Users have to keep all receipts so they can prove they are not usingmore than 2,500 litres a year if they are stopped in a roadside check.

Finding out whether your car can successfully run on the stuff is crucial. In general, older low-pressure diesel engines that appeared in cars made up until the late 90s are best. It’s not advisable to put it in modern high-pressure diesels sold in new cars as it may wreck the engine.

While the use of biofuels is the subject of a heated debate among environmentalists, some believe they are beneficial. You will need to take your own view before deciding whether to try it.

Patrick Whetman, who operates the detailed website says refined rapeseed oil is the best one to use in your car. His site lists the cars that have been successfully

run on vegetable oil over recent years. There is also an active forum which allows users to swap tips, and advise newcomers. He says many of the approved cars will happily run 100 per cent on oil once the engine is warmed up properly.

Some users install a second tank and switch to vegetable oil after a few miles. Others prefer systems that heat the fuel, which overcomes its lack of lubricity. Most users appear to run 20 per cent to 30 per cent on oil and the rest on normal diesel. “You won’t do much damage by trying it once — the damage comes mostly from prolonged use. Put

in a mix of vegetable oil and see how easily it starts. “It takes a while and if it produces a lot of white smoke, try a lesser mix or give it up. Fuel economy should be about the same: in some engines vegetable oils improve it, in others it’s slightly worse - about five per cent either way,” he says.

Reports on the various websites that are devoted to the subject have found that cars with Bosch pumps are much more likely to be able to runon vegetable oil. It’s important to establish the make in your car before using the stuff regularly.

John Evans, technical manager at the UK’s Society of Motor Manufacturers and Traders, agrees it is possible to run some cars on such oils but warns owners to be wary.

“It’s only older cars with low-pressure systems that can tolerate these oils. Newer, high-pressure diesel systems most certainly won’t. The problem is that there has been very little proper testing of the use of vegetable oils, so it’s hard to say with any certainty which cars will tolerate it.” He says users need to replace the fuel filter more often and be aware that vegetable oils can absorb harmful water vapour if left uncovered. “I think that most users will be better off using properly manufactured biodiesel. It’s much safer and offers a small saving.”

Alternatively, if you don’t live near a proper supplier but have access to a ready supply of waste cooking oil, you could always buy and operate your own biodiesel plant. Whetman’s website will sell you the plans to build your own.