Both engines will run on proper quality biodiesel (as opposed to biofuels, which can be any blend of veg/petrol/white spirits etc etc ). Avoid anything that isn't good warranted quality, as there is some really crap fuel sold as biodiesel, and some will wreck your engine.
The 300TDI will pretty much run on anything liquid (inc straight veg oil)though as its got a really tough simple injection pump and not much by way of electronics to confuse it.
The TD5 will be OK on good quality biodiesel, and I have seen reports about using veg oil in them. I'd not go with the veg route though as the pump/electronics are far too complex.
A quick way to get an idea of quality of biodiesel is to ask for a small sample.
First stick it in a jar. Biodiesel should be clear and generally look like apple juice, although colour varies depending on the oil its made of. Any cloudyness is a bad sign.
The viscosity should be similar to normal diesel.
Then stick an equal quantity of water (cold) in the jar, and give it a gentle shake.
The bio and water will mix briefly, then the water will settle out to the bottom.
If the water is even slightly cloudy the biodiesel contains soap from the production process. The soap will block your filter quickly and is generally bad for engines. You'd get away with a small amount in the 300TDI but not for long in the TD5.
Also when "going over" onto biodiesel, you would be best advised to introduce it gradually. Say first 200 miles at 20%, then 200 miles at 40%, 200 at 60% 200 at 80% or similar. Make sure you carry a fuel filter with you, and have tools/know how to change it at the roadside. This is due to the cleansing effect of biodiesel on your fuel system. All the crap in there will be loosened by the bio, and end up in your filter, blocking it.
If the filter isn't blocked by about 1000miles. change it anyway, as the system should be clean by then.
Enjoy.
Mark
