Well, here's what it is.
I would never, (I'll say that again) ~never~ put SVO/WVO through any of my diesel engines. There's no way I want trans-fatty acids inside my injection pump. I've heard too many tales of injector coking and ash deposits inside the combustion chamber to even want to experiment with my three rebuilt diesels.
Everyone I know who was fooling around with WVO has given it up and switched over to biodiesel. Even the people who were
making their own biodiesel have stopped and are fueling with commercially made biodiesel.
Part of this is due to the fact that digging around in smelly, greasy restaurant dumpsters is not all that much fun. The quality of the grease is wildly variable even within the same facilities output depending on how long the oil was used, what was fried in it, how hot it was, etc.
Filtering and clarifying your own "free" fuel is very empowering, but to tell the truth, I have a business to run and a bus to build, and it makes a lot more sense to go work for a client and then take the money and buy ASTM certified biodiesel which comes with a warranty than it is to spend time mucking around with nasty used grease. It's a young person's thing. Lots of time and youthful exuberance lend themselves to such adventures. Once reality sets in and the fun wears off, they all eventually find better things to do with their time. I know,
I've been there.
I can tell you that soon in the Portland, OR area, and after that in Tacoma WA, used oil will be scarce-to-impossible to find, as the output will be diverted to a new processing facility for manufacturing biodiesel. The old "help yourself to used oil" model is eventually going to be replaced by restaurants and food processing facilities leasing their oil from a supplier and paying the difference between delivered new oil quantity and picked up used oil quantity. This means that the lessee is going to be paying for any oil that "disappears" while in his care. You're going to begin seeing locks on grease dumpsters.
Road fuel and Federal Excise taxes: The bureaucrats aren't stupid. Right now, biodiesel and WVO/SVO are considered "fuel additives", and are mostly exempt from scrutiny over these taxes. I expect that will change when there's enough people using these alternatives to petroleum fuels. In the UK, home brewers of biodiesel can get seriously hammered with fines for not submitting the proper fees.
Second fuel system: Obviously, this is an expense to create and install. Once time investment if you don't consider that vegetable oil eats rubber like biodiesel does. Better use all synthetic hoses and fittings. Oh, and the first time you forget and let the fuel system cool down with veggie oil in the lines and pump, you'll be spending some additional time parked instead of driving while you attempt to heat the entire fuel system to get going again.
Fuel filter clogging: "Oh it's not that bad, I just pull over and clean/replace the filter and I'm back on the road in 10-15 minutes" -Common response of typical SVO/WVO vehicle driver.
When I total it all up, the possibility of engine damage, inconvenience of slopping around yucky used oil, likelihood of operation problems due to fuel system problems, possible legal repercussions, and eventual spotty availability of supply, I'll stick with commercially produced biodiesel. Of course, I'm a bit biased, being part owner of the largest distributor (and soon to be producer) of biodiesel in the Pacific Northwest,
SeQuential Biofuels.