So much has been written and said about "biodiesel" . . . and so much of it is bullshit . . .
I'll try to keep this short, but I encourage you to try to find two hours and do your own research (I can recommend
biodieselnow.com). I am not quite an expert, but I am damned close at this point, having been in the game for about 2.5 years.
"Biodiesel" has a specific definition: it's transesterified oil. The oil (feedstock) can be new or used, and vegetable or animal sourced.
What "biodiesel" (BD) is
NOT (not!) is just oil, or oil mixed with kerosene, or oil mixed with Sta-bil, or oil mixed with . . . you get the idea. BD is not oil
mixed with anything. If the feedstock hasn't been transesterified, it's not BD, period. If you don't believe me, you can argue with the National Biodiesel Board and the Feds, who made the definition.
In order to be sold as a fuel or as an additive, legally it should have to pass the BD ASTM specification D-6751. That's right, there's a series of defined tests (just as there are for petrodiesel (PD)), and if a test batch of BD won't pass the tests, it's not BD, it's homebrew or worse.
People are putting all kinds of crap into diesel engines these days, many of whom are doing it because they heard some things about "biodiesel" and thought they could save a buck, or save the whales, or boost local economy, or just hang out with other folks of like mind . . . and a whole lot of otherwise useful diesel engines are being scrapped as a consequence. That's my opinion, and I've seen enough of this to be convinced.
[ . . . pause to calm down . . . ]
Alternative diesel fuels these days fall broadly into three categories: BD (that which passes ASTM D-6751, and BD that doesn't quite); Straight Vegetable Oil (SVO) and Waste Vegetable Oil (WVO, which strangely enough includes non-vegetable oils, go figure) that are filtered somewhat; and gawd-awful SVO/WVO/bathtub-homebrew mixtures.
Each category has it proponents, advantages, and drawbacks. It's beyond the scope of one post by myself to do a decent job of even outlining all of those. Suffice to say that I am a very big booster of BD. BD (which is NOT VO/WVO) is a fuel which burns cleaner than PD (much lower HC, CO, particulate emissions (PM), and sometimes -- but not always -- slightly higher NOx in engines that have not had their IP timing backed off 1-2°). BD contains no sulphur, so no acid rain. BD has hugely enhanced lubricity over PD. BD smells a lot better (when burned) than PD -- as Philip says, it smells a lot like house paint in unburned state: linseed oil-like. BD is non-toxic and is not classified as a hazardous material (though the chemicals used in its productions definitely ARE) and you can just put a bunch on the ground and it won't do a thing. It degrades relatively quickly when exposed to air & sunshine (compared to PD). BD has a much higher flash point than PD, so it's less of a hazard to handle & transport.
BD can be produced, in quantity, domestically. If you research much, you'll find people who say it can't put a dent in domestic PD requirements, but they're ignoring algae (yes, algae) and Thermal Depolymerization (TDP), and you can Google those too if you're interested -- my point is that they're wrong, but lot's of wrong things get propagated in the internet.
BD is not fuel cells, but it can be put into the existing fuel distribution system NOW, whereas the "hydrogen economy" (which I believe to be a pipe dream, supported and propped in much the same way that Micro$oft props up Apple so they can point to Apple and say, "Look, we do
too have competition!") is pie-in-the-sky BS that is years -- many years -- away from any kind of mass use.
I'm biased: I've spent a great deal of time educating myself on BD, and I help maintain our local BD distribution point -- for fuel brought in from Seattle, and whose feedstock is soy oil from the Midwest. Stoopid, but true. The Seattle area has, I've read, the highest concentration of BD users in the US. I'm hours away from Seattle out in the boonies, but I can get our three 260 gal totes filled every month by a tanker that comes by.
Today, by far, most US BD is made from soy feedstock. Soy is not the best feedstock for BD production, it does not have as high a yield per acre as several other plants, and the fuel produced is a compromise of qualities -- there are better alternatives. However, raising soybeans is well understood in the US, and the soybean industry has a mature infrastructure that is partially subsidized by our tax dollars, so soy oil it is . . . for the time being.
Um, where was I?
The Datsun diesel 720s: I owned one '82 1.5 yrs ago that I bought ($400, from Mercer Island, 86k original miles) with a trashed transmission (read my other posts on this trans, it's the same guts as in the Maximas, and indeed as several other Nissan products for many years, and has several weak points), and I did a decent job of fixing it up, then sold it to a local ($2000). It has run B100 exclusively since I purchased it (1000 miles by me, 14k miles by the new owner), and if you've read the above, you know about at least a couple issues with B100 use and old vehicles.
I bought another '82 720 diesel four months ago for a friend ($160, Bellingham, non-runner) with a bunch of problems, mainly a stalled Injection Controller Motor and a lot of cut/bypassed fuel lines, and huge rust issues, still looking for a donor gas truck to do a drivetrain transplant), and after doing minimal work on it and getting it running well enough to vet the engine, I compiled a list of items it needs, and sold it to a coworker ($400), who is running it on B100 and also working down the list. It's a real timesink, but he wanted a small diesel PU, and there just aren't a lot around (for a pretty decent list I put together two years ago, see
this post of mine and scroll down about three screens worth to see the list.). It's not much of a PU, but it does what he wants.
I try to get local folks to see the long-term wisdom of BD use now.
BD is not cheap, if you don't own the feedstock. We are selling it for $3.49/gal right now. As BD goes, that's pretty cheap, and it's not (right now) competive price-wise with PD. It was actually cheaper than PD right after Katrina, around here anyway. But I don't proselytize BD on its economic benefits anyway.
If you have your own feedstock (or can procure it, as in fryer grease, donut shop oil, etc.), if you don't mind working with hazardous materials (lye, methanol, which combine to form methoxide, and it's not nice stuff to have in your basement unless you really,
really mind your Ps & Qs), and have the space and patience (and the ability to compost or otherwise safely dispose of the glycerin -- about 10-15% of the raw feedstock is going to convert to the base stock of bar soap!), then you can certainly save a pile of money by producing your own biodiesel. Lots of people are successfully doing it. There are excellent kit plans (Girl Mark has the best by far), kits, and entire fuel processors available for BD production -- and not a few rip-offs too, this being a fad kind of thing right now. There are all kinds of downsides too, but again, if you have the feedstock or can get it for a reasonable effort, and if you use enough fuel to make it worthwhile (say, fleet operation or home heating) then producing your own BD can make sense.
I have a whole list of things that I don't like about burning SVO/WVO and the crap that's being sold by one outfit that's supposed to "convert" feedstock to safe fuel without transesterification, but I'll spare you and admonish you to read a lot before going down the SVO/WVO and additives path -- beware, Luke, the Dark Side of the Force, etc etc. Burn glycerine and you get acrolein out the tailpipe, and injector coking, ring land coking, IP input shafts breaking, lube oil contamination . . . now there, I said I wasn't going to get into that list . . . do your own research, but I'm exciteable about the whole "put the fryer oil into your tank and drive" crap. Even Elsbett and Greasel don't convince me, they haven't got all the bases covered, but they're still selling a lot of hardware to hopefuls -- for the wrong reasons, IMO.
[ . . . more deep breaths . . . ]
As I've written somewhere else on this site, and on other sites, the Bosch (Diesel-Kiki, under Bosch license) VE IPs are weak: they leak. They leak in normal usage. They leak a lot faster when using "low-sulphur" (today's PD in the US) and "ultra-low-sulphur" (ULSD, we all get it nationwide in Sep-06 by Fed mandate). There is a thread on this site (and many others) on this topic.
I have run some B100 in my LD28, and now my IP leaks, presumably at the front seal. In my opinion, it would have leaked anyway but the B100 definitely pushed it over the edge fast. I still run B100 in it (it doesn't leak much, and I don't drive it 2k/year these days). I have the last (AFAIK) two NOS 1982 injection pumps available in the US, in storage -- I bought them for a song ($850 for the pair) two years back from a liquidator. My idea was to swap one in for mine -- this was before mine was leaking, mind you.
Now, if my leak is the front seal, I'll probably just replace the seal. I bought the
Bosch Book on distributor-type IPs (ie the VE series) and have read it cover-to-cover twice in the last month, and now know more about it than any sane person should -- it's not a rebuilder's book, it's all theory, and it's good, if you can get by the weird translated German. Recommended if you're interested in these critters, and it's only $23. Anyway, now that I understand the nine major systems in the VE IP, changing the seal is no big deal. And if I screw it up, I still have three other IPs with which to work.
[ . . . ]
Yeah, if you run SVO/WVO (or really bad BD that hasn't been washed well, or is not fully reacted), you will have problems getting the engine started -- and fuel system and overall engine life is reduced too, but most people only focus on the starting issue.
To my way of thinking, home BD production for home heating make more sense than for use as a vehicle fuel. But read up, there are drawbacks, too.
It's gotten late enough, and I have two other projects to research tonight, so I'll stop now. I'm not even going to proof this post, I'll edit it later.
.......
Although, if she tries to teach me about the washing machine......... That is a contraption I don't think is possible for me to understand 
