Last time I played with Straight Veg Oil the supermarket price rose to the point that it became un-economic. Coupled with my desire to run on oil that's really free, and not just cheap, I went for waste mineral oil instead.
Although I got the engine to run fairly well on old engine oil, the design needed further enhancements, mostly to the fuel pumping and heat exchanging stages. Unfortunately, these never got done as I've been very busy, and they haven't exactly been given top priority.
In the meantime, I notice that pump diesel has got dearer (nothing new there then), and supermarket veg oil has got cheaper, currently my local Tesco has oil at 83p/l. After inwardly debating the matter for a week or so, I've now taken the plunge, and Bitsa is back on DERV/SVO mix, currently about 2:1. If it does colds starts on that OK, I'll try increasing the mix a little, but I'm not planning on crossing the 50% mark for the minute - I need twin tanks to do that safely, as a bare minimum...
As I type
10 years ago