Have done quite a bit of reading on the subject, i have not run SVO in a diesel so for what it's worth. Heating SVO is to thin the viscosity of the oil so that it is about as thin as diesel fuel. And from what i have read and the people that i have talked to that have done it older engine designs are much more tolerant of thicker fuel. So if you are in a warm climate and have an old diesel you might be ok with out heating the fuel. If your engine is not tolerant of thick fuel you will damage the injectors $$ or the injector pump $$$$.

There is more information out there but here is a place to start,

http://journeytoforever.org/biofuel_library.html

In several of the posts have touched upon the salient points.

The original Diesel engine war designed and developed to run on peanut oil.

Yes the newer electronically controlled engines have tighter tolerances and are less forgiving of using straight vegetable oil.

There are 3 primary reasons for processing vegetable oils into bio-diesel.

First the process removes glycerin and other impurities above and beyond simple filtering. This makes it cleaner burning and more efficient. Since it is a relatively simple process. It is worth while to do. The only real problem is the initial expense of the equipment. But a good scrounge could easily over come much of these problems.

The second is viscosity. The process does thin out vegetable oil to more the consistency of commercial diesel.

The third is temperature tolerance. Diesel as well as vegetable oils have a nasty habit of getting thicker as the temperature drops. If it gets cold enough even commercial diesel gels to the point you can't pump it from the tank. That is why there are winter formulations for diesel fuel. It is also one reason many truckers leave their engines idling when stopped for sort periods of time. Such as rest stops and meals. The Bio-diesel process lowers this critical temperature somewhat for vegetable oils.

The reasons for preheating and the duel tank systems is to help over come this viscosity problem.

It is somewhat easier to start a more modern engine on diesel than vegetable oil. It simply takes more cranking to get the engine running on straight veggie oil. But it is do able.

It's true I live in SoCal where the normally warm weather is particularly conducive to veggie oil driving. As for where to get oil, we have a small network of local restaurants that give it to us. While it is becoming more valuable, more often than not restaurants are still having to pay to have it taken away by registered "grease" haulers.

There are very strict rules regarding the disposal of used cooking oil in Los Angeles county and I would imagine in most other parts of the country. It's not toxic nor is it dangerous but it is messy and the authorities don't want it poured down the drain and allowed to mix with the normal sewage here.

As for solidifying, true vegetable oil will solidify at whatever it's freezing point is, hydrogenated vegetable oil will solidify at a much higher temperature. There is no practical difference between new and used oil so far as solidifying in my experience.

The idea of pre-heating is the one which prompts most of the battles between the "2 tankers" and the "single tankers" in the veggie oil conversion world. There are solid reasons, no pun intended, to use either system. It all depends on the type of engine you're going to use, the normal ambient temperature where the engine will be used, how much money one wishes to spend, etc. One system that I'm planning on adopting is adding fuel line heaters to my single tank converted car. These are electrical heaters that are wrapped around the injection lines, they preheat the oil prior to it being injected into the engine. I've gotten very positive comments about using them from fellow single tankers even here in SoCal.

I will add that I am doing this using a 1985 Mercedes with the almost bombproof 5 cylinder engine. There are examples of these engines lasting for well over 500,000 miles. My current car has close to 400,00 kilometers on the original engine, it was originally a Canadian import and has a metric odometer and as I wrote earlier, we have had no engine problems that could be traceable to using veggie oil for fuel.

I would urge anyone interested in either trying this or learning more about it to research the net, there is a lot of info out there and more than just a little snake oil too.

John E