If you want to start looking for a diesel vehicle to convert to use veggie oil, you'll want to do your homework.  Only 5% of passenger vehicles in the US are diesel, and those who own diesels tend to be like Mac users:  a small but loyal group.  Here are some things to consider before you begin your search:

*Buying a new diesel:*
In Massachusetts you cannot currently buy a new diesel passenger car due to emissions regulations.  This is ridiculous because you can buy diesel pickup trucks that probably have worse emissions and comparably terrible mileage.  The latest diesel emissions technology, such as in the VW TDI (Turbo Direct Injection) engines, is very clean-burning, nothing like some of the old diesels from the 80's that spewed black soot out the tailpipe.

In June of 2006, a new low-sulfur diesel will be sold at the pump.  Hopefully this will help change the law restricting new diesels in MA.  I've talked to the local VW dealer and they don't really care either way.  There are plans by several major car manufacturers to release new diesel passenger cars in the US in the next few years, so that may be the changing factor.  Take a look at http://www.businessweek.com/autos/content/feb2006/bw20060214_419891.htm to see what's coming.

*Emissions:*
A lot of the older diesels are more polluting, for example a lot of the older Volvos, Mercedes, and VWs from the 1980's.  Turbodiesels such as the VW TDI's burn the exhaust gases for extra power, which reduces the emissions further. (plus gives it more pep)  Check out  http://www.honda.co.uk/change/ to see the Honda Accord diesel already released in Europe, hopefully soon in this country.  It's supposed to have incredibly low emissions.

*Age of Vehicle:*
Diesels live a long life!  The fact that there are so many 25 year old Mercedes that are still going strong is a good testament to that.  It is not uncommon to see a 1980 Mercedes sedan with 250,000 miles selling for a few thousand dollars.  I paid more for my Beetle than a comparable gasoline Beetle; they don't depreciate as quickly.

If you are going to buy a used diesel, you should consider what age vehicle you're comfortable with.  In my case, I drive a lot and didn't feel comfortable buying a vehicle with a few hundred thousand miles on it.  If you're not going to be driving many miles each year or are car-mechanical, maybe you'd be more comfortable with a high-mile vehicle than me.

*Image:*
This may seem like an odd factor when choosing a car, but it was a deciding factor for me.  A lot of those old Mercedes look NICE; they were sold as luxury cars.  As a piano tuner, I had to consider how it would look for me to pull into a customer's driveway in a luxury car.  What image you want to project may be something to consider.

*Fuel economy:*
Like I said earlier, diesel engines usually get much better mileage comparatively than gasoline engines.  I was visiting the VW dealer for a timing belt and wanted to cause trouble, so I walked around the showroom floor and saw their new floor model Beetle (gas) is rated to get 25mpg, compared to my 50mpg - same car, different engine.  I can't believe they're not pushing to get diesels in this state, with the craze of hybrids and high gas prices.  Really, I've talked to several salespeople and they could care less.

*Safety:*
A friend of mine who works on Mercedes holds this as the prime factor in selecting a car.  For this reason above any others, he recommends Mercedes.  The newer VW's also have very high safety ratings as well.  I'm no expert on the safety features, but the older Mercedes _are_ missing the newer safety improvements such as airbags, so there may be a trade-off.