I met someone, today, who is running his 5 cyl, turbocharged Mercedes
300D diesel car on free vegetable oil using the Frybird system:
http://www.frybrid.com/svo.htm

The car starts on diesel fuel and must bring the veggie oil up to +160F
and the engine up to operating temp (180 thermostat) before switching it
from diesel to veggie. The webpage explains why.

He invited me to take a drive with him to show off his handiwork.....

As the engine warmed up and the heat exchanger in the small portion of
the fuel tank reserved for heating the fuel got hot, a short time
actually as the car was already driven when I met him, the microprocessor
in the system simply switched us to veggie oil at 160F, where its
viscosity drops to near diesel fuel thinness. At first, until the diesel
fuel had purged from the injection pump and lines, I didn't notice much
difference. The transition is very hard to detect as the throttle still
operates exactly the same on veggie as diesel at this temperature. But,
after the lines had purged, we drove onto the interstate. "Floor it!",
he told me. "This is a 300D?", I asked, confused. 300D, while more
power than my little 220D's 57 blistering hp, isn't going to throw anyone
out of their seats on acceleration. This 300D, however, had LOTS MORE
power than my 300TD wagon on diesel! We were cruising down the
interstate running on pure vegetable oil from a Chinese
restaurant!....FOR FREE!...AT 80!...

Most impressive.....

He's now draining the oil from 8 restaurants into a 55 gallon drum on a
trailer when they call him. I didn't see his filter system, but he's
running a "fuel polisher" similar to the ones used to clean the fuel on
the docks of algae and gook on its way into the veggie oil tank mounted
against the back wall of his 300D sedan's trunk. It holds 21
gallons.....enough to go about 1300 miles, according to the other users
on Frybird's forum on the website. The old 300D ran really smooth with
very little smoke, no more than it did on #2 fuel oil.

No, it didn't smell like a stir fry Chinese meal, either.....(c;

I see a Hatteras with twin 8V92TA's riding down the harbor burning 20
gallons of waste veggie oil per hour.....for FREE....

Of course, if it catches on, veggie oil will be $8/gallon at the back
door of Wong's Wok 'n Grille in every town. But, it'll be nice as it
lasts. Before he was hauling it away behind the 300D for free...the
restaurant was PAYING someone to haul it off. They're very happy to give
it to him....

--
There's amazing intelligence in the Universe.
You can tell because none of them ever called Earth.