It's been a while now since I've been running on waste veggie oil, virgin veggie oil and diesel in my Landy. The 300TDI engine is just so basic it seems to lap it up without any concerns, but about 10K miles on here is my summary to date:
My random notes:
a. I replaced my heater plugs as the starting was a nightmare – whilst doing this I discovered that none of the heater plugs were actually glowing or getting warm! and by the look of some of them, they hadn't been for some time (well before the veggie conversion I'm guessing). New plugs are in and everything starts first time – even on pure veggie oil at 3-8 degrees outside temp.
b. IMHO technically Waste Veggie Oil is much much much better. It seems to burn cleanly, give good performance and leave little smoke. Normal virgin veggie oil is ok and seems to give a performance akin to Diesel but I've only gone through a small amount of the stuff. Of course the best way to use veggie oil has to be by using local waste veggie oil – so I'm not sure if I'm evaluating my estimate of performance of the waste oil on my moral interest in localisation. Either way it does seem to be the best.
c. The glow plug part of the veggie oil conversion seems to provide the best boost in starting and early running performance. The hot water side helps later (but almost by then the engine is already warm and handles it much better anyway).
d. Best ratio of veggie oil to diesel so far: Warmer temps (+10 degrees C) 100% veggie oil no problems. Cooler (0-10 degrees C) 60% Diesel 40% Veggie Oil. Cold (-8 – 0 degrees C) 98% Diesel 2% Veggie Oil. There is nothing scientific about this – this is just what I've experienced. With my heater plugs changed it may well allow me to run higher mixes.
e. Be pragmatic – use an injector cleaner regularly, don't expect miracles, and don't expect to make all your money back in one or two tanks – it's about the environmental savings as well you know.
f. Last thing… getting hold of waste veggie oil is getting very difficult!