With petrol prices poised to soar again this summer, anyone like me who has already tried to run a car on waste vegetable oil could have much to feel smug about.
The AA has been warning drivers of another summer of "petrol madness", as rumours spread of oil prices hitting $100 for a barrel of crude. But after driving my ageing Merc on waste vegetable oil for the last 18 months, my smugness is mixed with realism. There have been too many "un-smug" moments, like the day I found myself late for a wedding while creeping along the M40 at 45mph and unable to go faster thanks to a fuel filter crammed with kebab fat. There are too many items in my wardrobe with a dubious bouquet and my hall carpet has acquired a worryingly deep-fat shine. But there is an upside - I can now drive anywhere in the country for pennies.
I bought my Mercedes 190 2.5 diesel for its mechanical simplicity and comfort. But after running it for a while someone suggested that I should try it on vegetable oil. "Old diesel Mercs are ideal to run on veg," he said confidently.
After researching conversion methods, I played safe and opted for a twin-tank vegetable oil conversion, rather than just pouring filtered waste oil into the fuel tank. A twin-tank route means that you can start the car on diesel - which flows from a marine plastic tank in the boot - until the engine is warm enough to suck the thicker, heavier vegetable oil from the main tank. A company called Regenatec - which recently stopped trading - sold me a Smartveg conversion kit for £520 and I paid a garage £400 for a garage to fit it. Total cost? A bit more than £1,000 after the addition of a heated fuel filter. It seemed like lot of money to spend on a car that hadn't cost much more than that to buy. But, if the car held up for a few more years and I could find a chip shop willing to offload its used oil for free, I'd be quids in.
That was 15,000 miles ago and the twin-tank conversion route is one that, on balance, I now slightly regret. It works well for many cars, but the Smartveg system brings with it some under-bonnet plumbing that needs periodic maintenance. Some of this now ageing plumbing is, I suspect, responsible for recent air leaks that have compromised the engine's smooth running and starting. However, the twin-tank approach is kinder to the engine, especially in winter, and is essential for more modern engines, though my car could have coped without it.
I find that I have more than broken even. A local gastropub now supplies me with 120 litres a month of its KTC-branded waste oil for no charge. If I wanted to - allowing for a tiny bit of diesel use at the start -I can drive from London to Inverness for about 75p. When diesel prices were peaking, this trip would have cost me £75. The savings can be sensational.
Running your car on vegetable oil - be it a modern turbo-diesel or a battle-scarred veteran with more than 200,000 miles on the clock, like mine - can be a labour-intensive business, especially running on waste oil. Twice a month, I have to lug several 20-litre containers up from my local's cellar before dropping them in the car boot. Back home, the oil is decanted into a 200-litre plastic tub kept in my cellar via two five-micron sock filters, which handily keeps the fried onions and chicken wings out of the car's fuel tank. (Another restaurant that I rapidly weaned myself off offered me plastic tubs full of gelatinous pieces of meat run aground in their own fat. Unusable.) This vegetable oil is then pumped into 10-litre containers and finally poured direct into the car's fuel tank via a plastic funnel. Simple enough, though time consuming.
Overall, then, is it worth going veggy? The answer has to be a highly qualified "yes". If you can't face running on waste oil, the cost savings on new veggy oil aren't nearly as attractive. When I converted, vegetable oil from Tesco cost 45p a litre, a figure that has now more than doubled. Running your car on new oil is also pretty ruinous for the environment.
If you are determined to go the waste oil route, prepare to get your hands greasy changing fuel filters regularly and expect teething problems, not to mention some disgusting decanting experiences. Most modern diesel engines are direct injection units and generally will not thank you for running on waste oil. A TDI, TDCI or HDI moniker on the back of your boot generally denotes direct injection. However, most older diesel Mercs, VWs and some Renaults/Peugeots/Citroëns should be fine as long as long as - and this is crucial - the engine is an indirect injection unit. So do your research carefully.
Running on waste veg is increasingly coming under threat from biofuel companies keen to collect previously unwanted old vegetable oil and turn it into healthy biodiesel profits. So you may have competition, not to mention from other people, also driving on fat. Try schools and old people's homes, which also are likely to change their oil regularly. For the moment, it's still possible to turn yourself into an oil baron.
Oiling the legal wheels
Have you tried running your car on vegetable oil? Share your experiences by writing to Cash, The Observer, Kings Place, 90 York Way, London N1 9GU, or email us at cash@observer.co.uk.
To stay on the right side of the law, you need to complete a waste transfer note from the Environment Agency (there's a template at environment-agency.gov.uk) when you collect waste oil. But don't overdo it; if you collect more than 2,500 litres a year, you'll be liable to pay duty on all of it.
The website vegetableoildiesel.co.uk is a hugely helpful resource, particularly the discussion board. Biotuning.co.uk is another useful site.