Capetonian Roy Dibley runs his 1980s diesel Mercedes on used vegetable oil, collecting it from restaurants in and around Cape Town. Sometimes he pays for it (R1.50 a litre, which is its price as an additive to animal feed). Sometimes he gets it for nothing.

Dibley reckons it costs him about 50c a litre to filter it before he can put it in his tank - which explains the sticker on the rear of his Merc which announcess that he is running his car on fuel that costs R2 a litre, and that anyone interested in doing the same should ring his cellphone number.

Dibley is a qualified mechanical engineer who designs, builds and sells conversion kits for diesel engines to run on vegetable oil (after filtering) - used, or neat, straight out of the bottle.

The kits, which have been extensively tested in South Africa, are now available from Dibley, and he hopes they will prove a boon to farmers large and small, to operators of hotel courtesy buses and, as he puts it, small operators like plumbers and electricians.

One of his first kits, which he fitted to an electrician's 280KB diesel bakkie, is performing well. The success of these prototypes led to the formation of a business partnership between Dibley, Stuart Freedman (based in Britain) and Valentine Lefrère, an entrepreneur and venture capitalist. Dibley's vision of the product's potential is broader than the luxury market of campers, converted buses or diesel Winnebagos, if there are such things.

"You don't convert a new Mercedes or a new BMW," he says.

"What you do convert is a diesel engine that does not have electronic fuel injection.

"The opportunities are immense for farmers, who could plant oil-producing plants. Peasant farmers could form co-operatives and do it on a smaller scale.

"With the price of conventional diesel fuel approaching R6 a litre, it even makes cooking oil fresh off the supermarket shelves attractive as an alternative."

Fresh cooking oil?

"Yes, indeed. Vegetable oils are more suitable in many ways. In fact, they are better lubricants and produce more torque when used in diesel engines," says Dibley.

What about damage to valves and pistons and other engine parts?

Nothing harmful, he insists.

Not only is vegetable oil a better lubricant, it burns more efficiently and emits fewer particles into the air and shoves out less greenhouse gas.

It is true that in colder climates, with their severe winters, vegetable oil tends to thicken. In South Africa it never gets cold enough to be a problem, but neat vegetable oil still has to be heated to increase its ability to vapourise.

Hence there are two fuel tanks in the system - a small 20-litre one for old-fashioned dieseline (small enough to occupy a small nook in the boot or under a rear wheel arch) and a second one, which is the standard vehicle tank, to take the vegetable oil (new or used and always pre-filtered).

Starting up in the morning, you use dieseline, says Dibley. That quickly heats up the vegetable oil and, by the time you have driven 500m, you can switch to vegetable oil.

Last thing before you park the vehicle at night, you do the same thing, switching back to dieseline for the last 500m of your journey.

But how much dieseline has to be carried? According to Dibley, a full start tank should last you about 20 days.

There is still a question about engine damage.

"Well, all diesel engines have to be serviced regularly," says Dibley. "Vegetable oils have no sulphur at all and far fewer solid particles than regular dieseline; however, I would still recommend oil and filter changes as per the manufacturer's instructions."

What about availability?

According to Dibley there is plenty of waste oil to be found - every place that sells cooked food will change their cooking oil about once a week and it all has to be disposed of.

"Think of all the farmers, small operators like plumbers, electricians, courier delivery vans and hospitality buses, even army vehicles, who could switch over.

"This would save the country a lot of foreign exchange for one thing and help save the environment for another. And then there are all the jobs you could create by growing soya beans, canola or sunflowers for the oil.

"There are also jatropha trees as another option. They grow where only 300 millimetres of rain falls every year, animals don't eat it and 40% of the jatropha bean is pure oil."

But what about availability if many people switched to either used or fresh vegetable oil?

"Ah," says Dibley, "there is a worldwide glut of vegetable oil right now; so we could always import it. South Africa could be a world leader in using vegetable oil, a renewable fuel resource, rather than normal diesel oil, which is a fossil fuel."

The conversion costs R4 999 plus R500 to install it - or less if you do it yourself. There is also the DIY home filtration system available at R2 395, with extra filters.

For more information e-mail Dibley at KBAC@mweb.co.za